There is an error at 1:21. The example given is not an action/reaction pair. (Gravity and Normal Force). The normal force can often be more or less then the gravitational pull on an object. For example, if you lean on a desk while sitting in your chair, the normal force from the chair will be less then your weight since some of the weight is held up by the desk. Action/reaction pairs are always equal in magnitude. The other clue here is action reaction pairs never act on the same system. The normal force from the chair is paired with the normal force from your body onto the chair. Two separate systems. Please either edit or have a floating comment as this is one of the most common misconceptions for students. Thanks.
Yes! Professor Dave - careful, the normal force and the gravity on the person are not a third law action-reaction pair. They are acting on the same body (the person). Third law action-reaction pairs act on different objects. The earth pulls on you and you pull up on the earth with the same force. The effects on each are very different. The pair from the normal on you (upwards) is the normal of your body on the chair (downwards).
I have a different view on this. As you said when a body falls to the ground, it accelerates to ground and earth also accelerates a minuscule amount towards the falling object. Similiarly an action like a person jumping on the ground causes the earth to go down a minuscule amount since mass of earth is very high compared to the mass of the person. This is as per Newton’s III law of motion. In this example when you strike the hammer on nail, there are two different types of force on the nail. One is the normal gravitational force on the hammer. The other one is the downward force the striker exerts on the hammer . The normal gravitational force on the hammer has an effect on earth same as a body falls to the ground. When the striker forces the hammer down he is applying a force more than the gravitational force on hammer. In this case the force opposing the striking force as per the III law will be on the body of the striker . The body will go up a bit. If the striker stands on a weighing scale you will notice the scale dipping a bit.
Uh oh, the normal force on you from the chair is NOT the Newton's 3rd law "equal and opposite reaction" (counterforce) to your weight, even if it happens to be equal in magnitude and opposite in direction. Instead, the other member of the action-reaction pair is your gravitational pull up on the Earth. Action-reaction pairs (1) act on different objects and (2) must be of the same type!
This is the one thing keeping me from showing this video in my physics classes! I don't need my students to get confused that the normal force is a reaction force to the Earth pulling down on the person...
If the Earth pulling down on the person is the action force, the reaction force is the person pulling up on the Earth. An action-reaction pair is always two objects interacting with each other.
Professor Dave is a fantastic teacher, but thank you redbaron07, as soon as I saw that error, I went to the comments hoping someone would correct the good professor.
Hi! I wound like to point out that in min 1:30 for me the video seems to imply that the normal force is the reaction of gravity . That is not true. The reaction of gravity is gravity itself. And the reaction of the normal force is another normal force. What happens is that while you are being pulled by earth ('s gravity), you encounter the earth's surface and your accelerated body pulls the ground down. The ground returns the favour by pushing you up. That is the normal force. To see that clearer, notice later in the video: the reaction never acts on the same body as the "original" force. Therefore, normal force is not the reaction of gravity.
I thought the same exact thing. I think this is why the 3rd law gets confused so much. People think it's the normal force that is the reaction force but it's not. The last part in the video clears it up a little bit I think. Nice catch.
1:18 this is NOT an example of a Newton's Third Law pair. both the Force of Gravity and the Normal Force are acting on the person sitting in the chair. Newton's Third Law requires two objects.
The equal and opposite force is not between the hammer and the nail but rather, the source of the force, your arm, against the source of the opposite force which stops the force of your arm, the wood. Hope this helped!
so clear and comprehensive, dave clearly knows the common misconceptions and misunderstandings of the third law. helped me clarify when the topic seemed so fuzzy i didn't know where to start or what to fix. thanks sm dave!
Thanks for the help Mr. Dave, your videos are fun and entertaining to watch, also, they teach me very well my lessons! I hope you are doing well at this difficult times, and I wish you luck.
hello appreciate the video. But I have one thing to clarify. The example you mentioned with the chair has a wrong part I guess. The third law states that every action force has an equal and opposite reaction force, BUT with the same TYPE. So the real reaction force to the gravitational force acting on the guy sitting on the chair is the gravitational force of the guy himself not the NORMAL force of the chair. Since the NORMAL force is not the same type of the GRAVITAIONAL Force. thanks for reading this and please correct me if I am wrong.
You're right. Normal force of chair on you and "normal force of you on chair" are a third law pair. "Earth pulls you" and "you pull Earth" are another third law pair. Just because two forces happen to be equal and opposite doesn't make them an action-reaction pair.
Hi Dave, what is the time span between the action and the reaction? (when your answer will be "none" then: is the force of the reaction when the first atom of an object (1) interacts with the first atom of another object (2) equal to the force of the reaction when the last atom of object 1 interacts with object 2?
i always thought the 3 laws are best understood when learned in reverse order ... when students get to the first and final law, they are relieved that there is nothing happening to the object and no more equations to learn
So does the nail experience more acceleration than the hammer? A=F/m, (the nail has more net force than the hammer). Like bowling ball and pin, if they both have equal and opposite forces, what net force moves pin away from the ball? Acceleration? A=F/m if F is equal on both objects, one with smaller mass will accelerate more than larger mass object.
when hammering a nail into a piece of wood the hammer imparts force on to the nail and the nail imparts force in to the hammer but the nail is drivin because there is a net force acting upon the nail from the motion of the hammer likewise the hammer has two forces upperating upon it the downwards force from your arm and the upward force from the nail that's why when you strike the nail, the hammers stops moving at roughly the location where the impact to curse so if we looking for the nail we only consider the forces acting at the nail if looking at the hammer we only consider the forces acting at the hammer
ah, so the forces are equal, but because the bowling pin is more massive it experiences a much smaller change in acceleration, whereas the bowling pins are much lighter, so they experience a much greater change in acceleration.
"but because the bowling pin is more massive it experiences a much smaller change in acceleration" and then "whereas the bowling pins are much lighter, so they experience a much greater change in acceleration. "?? explain please
DARK INFERNO i think he meant the bowling ball is more massive so the acceleration does not change as much as the bowling pins, which have less mass. This makes sense if both forces are equal and force equals mass times acceleration.
Let's suppose a body has mass of 5 kg and has velocity of 10 m/s...this body collides with another body of a bigger mass of 10 kg....but by law of conservation of momentum we know that product of mass and velocity of one body is equal to product of mass and velocity of another body if the two bodies undergo interaction....so the body with mass of 10 kg will experience a velocity of 5 m/s because of the law of conservation of momentum... Same way the bowling ball has more mass than bowling pin but since they r in interaction, their product of m and a(acceleration) will be equal ,i.e, if bowling ball has more mass than bowling pin then bowling ball's acceleration must be smaller than bowling pin such that their forces are equal.
I think the statement at 1:19 is incorrect as it suggests normal force and gravity are force pairs which I believe isn't the case. Please correct me if I'm wrong.
So if I clasp my hands together, are there 2 forces (each hand pressing against each other, acting as force pairs for one another) or 4 forces (both hands pressing against each other, and the force pairs for both forces)
Students beware, this video is clearly not well thought through. Anyone who knows a little bit of physics knows that 'these forces are equal so the car stops' at 1:05 and the so-called action-reaction pair example at 1:27 are serious misconceptions.
Mistake??? I think relation between the gravity and the normal force does never never example of action and reaction. How do you think about this ,Dave?
more correctly we can think of it as the normal force of the object on the earth and the normal force of the earth on the object, but yes this is how newton's third law works!
The force of gravity is an action force that is caused by the earth's gravity on the man. The reaction force would the be the force of gravity from the man acting on the earth. The normal force acting on the man is a separate force entirely. It would be paired with the normal force from the man on the chair. For example: On ramps, the force of gravity points straight down toward the center of the earth, and the normal force is perpendicular to the ground, so at some angle. In this case, the normal force and gravity are both acting on the object but are not equal. Falling objects also have a force of gravity, but do not have a normal force. In summary, the force of gravity and the normal force are independent of each other and do not cause one another, therefore they are not force pairs. (Though they each have a respective force pair.)
Another rule of this law is that the forces are acting on diferent objects. The gravity and the normal force are acting on the same object. This is not a good example.
you are totally right. it is a common misconception that the force of gravity and the normal reaction are considered as action and reaction! and no, professor dave, it is not how newton's third law works!
Really sir you have cleared my all doubt 🤩, I have watched 10-11 videos but my doubts had not got cleared from them. Even my teacher didn't cleared my doubt😔 But you are awesome 🤩🤩🤩🤩
Can the third actually be explained by intertia? That, because an object will "want" to remain in its current state of motion, the normal force is just the object's resistance to a change in motion? Although, that would make the normal force a fictitous force, which doesn't seem right. Am I conflating two different things?
You are conflating two different things. The forces acting on the same object, adding up to zero, is Newton's first law, the law of inertia. Quantitatively, inertia is the m in Newton's second law, that is a body's resistance to accelerating. Newton's first law is a special case of Newton's second law, when the forces add up to zero. The normal force is not a fictitious force. It is caused by outermost electron-electron repulsions, between two objects that are attempting to crash in to one another. The two forces acting on two DIFFERENT objects, that are mirror images of each other, is Newton's 3rd law. This is the law that says that forces are a two way street. You cannot push without being pushed, you cannot touch without being touched. Earth pulls on you, and you pull on Earth. The only reason you move instead of the Earth, is that the Earth has a hell of a lot more mass, and doesn't move anywhere near the amount you do, when responding to the same magnitude of force.
My question is, why did the planes on 9/11 sliced right through steel and reinforced concrete flooring without breaking a piece? Not to mention, that plane is way weaker than the tower. The plane literally flew inside the tower without damaging itself, this is impossible according to the 3rd law, right? To this day I’m very confused about hollow aluminum planes slicing steel.
Well, the notion that the plane flew inside the tower without damaging itself is pretty absurd. If it's going fast enough, anything could do massive damage. This should be common sense. You're only considering the materials, and entirely ignoring that one of those materials was going really fast. Do you expect it to just bounce off?
Willoughby Krenzteinburg Look at the slow motion you won’t see a single piece breaking off. Two, wings and tail section would snap on an impact, yet it doesn’t do a single damage to the plane. Birds do more damage than steel and reinforced concrete. Nobody says it should bounce off, but you should at least see the debris falling when the plane impacted with the tower. Like I said, go watch it in slow motion and you literally see a plane slicing right through the towers.
@@moto__shark I've seen it, and you DO see debris falling. What is it you expect? An entire wing to fall intact after colliding into a building at 600 mph? It looks like exactly what a reasonably educated person would expect when a plane collides with a building at close to 600 mph. You're not adding anything new to your argument here, you realize that, right? Your counter is just "watch it again". There are zero structural engineers or otherwise qualified experts who would endorse what you are saying.
Willoughby Krenzteinburg 600 mph? Planes cannot fly at such speed at low alt. Air density is too thick. Any educated person knows that commercial plane have turbine engines, not jet engines
@@moto__shark Good Lord. Both planes were 767s which used jet engines. The first plane was going 494 mph. The second plane was going 586 mph. These speeds were analyzed using the footage available - which you clearly have access to. Denying this just makes you blindly and willfully ignorant; nothing more. There is absolutely no reason planes would be unable to reach these speeds. You're just literally making shit up as you go along, and are oblivious to how absurd it is. What is it you are getting at anyway? Is your argument that they were not really planes....even though literally millions of people saw the second one as it was aired live - not to mention thousands in person? Is this what you are saying? Wasn't a plane?
if it was a prime example of the third law then wouldn't the parachutist stay in place? perhaps that's why? ofc, everything could be an example of the third law but maybe it's not a prime one?
@@solomeen6512 Common misconception. Newton's third law pairs of forces do not both act on the same object. There are N's 3rd laws involved for a skydiver, as the skydiver will cause a downwash of air, from the air applying the drag force to the parachute. You can feel a downwash of air from aircraft flying above you, which is the equal and opposite reaction to the air providing a lift force to the wings. This is why the "birds in a truck" thought experiment, doesn't produce any lowering of weight of the truck as a whole. The birds flap their wings for a lift force, and the wings push downward on the air. The reaction to the wings pushing air down, is that air pushes the wings up. On net, a truck full of birds will still weigh the same, even if the birds fly inside instead of sit inside.
Resultant means the result of a vector math operation. In this case, it means the vector sum of the forces. Place the vectors tip-to-tail, and connect the first tip to the final tail, to find the vector sum of forces, i.e. net force. The i/j/k refer to coordinate unit vectors, and have a hat like this: ^, written on top of them. I.e. vectors of magnitude of 1, that are used for keeping track of the components of vectors. i is defined as the vector along the x-axis, j is defined as the vector along the y-axis, and k is defined as the vector along the z-axis. If you are wondering why we use that particular trio of letters out of all possible letters, it has to do with Hamilton and quaternions. He came up with a concept that extended imaginary numbers in a way that could replace vectors in general. The three letters for the unit quaternions along each of the three axes, would all be a version of the sqrt(-1). What I call, the imaginary, joke, and kooky numbers. It didn't catch on to the extent he had wanted, but the notation still stuck. Some books use x-hat/y-hat/z-hat, instead of i-hat/j-hat/k-hat, to represent cartesian unit vectors.
There is another force on the nail by the wood called Fwood. Fhammer > Fwood forces the nail into the wood. Farm is really confusing. It should be part of Fhammer and should not be added.
Prof Dave please correct your mistake on the normal force and weight being an action reaction pair. A lot of students are watching your videos which are very good so a correction would help them.
Light can break Newton's third law: Wimmer, M., Regensburger, A., Bersch, C. et al. Optical diametric drive acceleration through action-reaction symmetry breaking. Nature Phys 9, 780-784 (2013). DOI: 10.1038/NPHYS2777
I think you implied that the normal force of the chair was the reaction to the gravitational force pulling you down toward the center of the earth as you sit on the chair. The reaction would actually be your body pulling up on the earth's mass. I think that normal force is the force that is balancing the pull of gravity and putting the chair sitter in equilibrium -- a Newton's 1st law thing.
Gravity has not been determined whether it pulls or pushes, The jury is still out on this/.... as Newton and Einstein are not in agreement .. newton thinks it pulls down and Einstein is a fan of push.. to teach students that it is a pull when its not been settled is probably not fair.. these students will think they have the correct answer as the prof is the teacher... and the teacher is always right... hmmmm
I was just thinking the same thing. But I’m still annoyed about the concept that for newtons 3rd law would seem to imply that no object could ever move, since any force accelerating an object must be paired with another in the opposite direction. For this reason we consider only the forces acting upon another object, and not the forces acting upon other objects. So if a person pushes a box we only consider the forces acting on the box. When looking at the person we only consider the force acting on the person. Okay, but this doesn’t ignore the fact the person is still experience a force the same amount of the box. That’s basically saying hey, just focus on what the objects are experiencing instead of worrying about why they are experiencing them. I find it odd that a person with less mass can push an object with more mass. That means the force the person with less mass applies to the box is great enough accelerate the larger mass. But if we look at the same force coming back at the person who has less mass the person isn’t being pushed backwards right? No. It’s odd that only the object being put into motion continues to be the object in motion.
@@ariel_12354as for the person pushing on the box. Yes it’s true that the force they push onto the box comes back to them. The reason the box moves is because it experiences enough force to overcome it’s maximum static friction with the floor, but the maximum static friction between your feet and the floor is higher, so you don’t slide back. It sounds weird because the box has more mass, but it’s due to the friction between the box snd the floor and your feet and the floor. Watch a video on static and kinetic friction
Hi Prof Dave, I love your videos and use them a lot in my classes. I would like to add one comment to this one though. Where you are explaining the force and counter-force acting on the sitting person, it is not exactly precise to state that the normal force is the counter-force of gravity. Gravity is the attractive force by the earth's mass on your body mass, thus the counter force to this would be your body mass attracting the earth vertically upwards. The normal force by the chair's surface on your butt has its pair as your butt is pushing against the chair -due to gravity. I would recommend this little change here, because to me what you have is a bit misleading. Force and counter force must act on different objects via an interaction. Gravity and the normal force are both acting on the sitting person, thus creating balance.
This is an EGREGIOUS error (as with 'these forces are equal so the car stops' at 1:05). To be honest, I can't imagine why these videos would be shown in any class if he has not addressed these mistakes in over a year.
Im still confused, what if when two objects collide, both of them exert a force, so the 'action' has 2 forces, so does that mean there are 2 newton's third law, you know what i mean? Like from all the videos i have seen is always If Object 1 exerts a force on object 2, then object 2 exert a same and equal force on object 1, but what if when object 1 exerts a force, object 2 does it too
can somebody answer me this question : horizontal acceleration : -9.8m/s^2, normal force = -gravity's force, gravity's force = m*a, if so, is the normal force always increasing by the second? because gravity is increasing every second?
If the horizontal acceleration is -9.8 m/s^2, then this means that there is another force in addition to the object's weight, that is equal in magnitude to the object's weight acting on it to accelerate it sideways. And in the direction we assign as negative, traditionally west or south. Given an acceleration that is exclusively horizontal, than this means vertical forces have to add up to zero. So some other force, like the normal force would be upward and equal in magnitude to gravity, so that vertical forces add up to zero. In this example, it is just a coincidence that gravity would be equal in magnitude to m*a. Usually, that happens when the object is in free fall, rather than accelerating horizontally. Accelerating horizontally would require another kind of force to cause this acceleration. Gravity is not increasing every second. Its speed could be increasing every second, but don't confuse speed increasing with gravity increasing.
If only I had seen this video when I first started learning about Newton's 3rd Law of Motion, it wouldn't have taken me 8 months to get comfortable with it. By the way, I've heard a(n) (unsubstantiated) story that Newton had trouble with his 3rd Law, as well. Does anyone know if this was true?
The Third Law Pair with a person's weight is the force of gravity on planet earth from the person, not the normal force. What about freefall in that case? And force pairs never act on the same object!
Yes, it would. And then it breaks down to which is most able to resist the force applied, the hammer, the nail or the wood. This is also why, at some points, a nail bends instead of actually driving (deeper) into the wood.
The laws that are in FORCE by false entities cannot be binding because of the laws very own definition by use of word manipulation. This allows that law to mean one thing for one and different for another. Also one cannot be accountable for a law enFORCED as they are withheld from the people. Where as a commandment, if not covered or only apparent, allows one FREEDOM of will to make an informed morally based decision to obey
Sir can you please explain that what happens when we lift an object take for eg a chair so we apply a force on it in upward direction to lift then how does it apply a reaction force on our hands
When you a force upwards like lifting a chair the reaction is applied on the ground by your legs and ground should down in micro level. Something like jumping up and the force in the opposite direction is ground, which is small and not not noticeable.
Counterintuitive I know, but it's true! The confusion is rectified when you realize that F = ma applies. Same force, not the same mass so not the same acceleration.
One day, I’ll finally remember why the third law doesn’t imply that nothing should move, because of systems and because a=F/m . Until that day, I’ll keep coming back here like once a year I guess
A hot air balloon rises, because there is a force of buoyancy that exceeds its weight. This is caused by an accumulation of air pressure that adds up (integrates) to exceed its weight, in response to it pushing its volume worth of air out of the way. The air pushes the balloon up, and the balloon pushes the air down. That is the Newton's third law pair involved in making a hot air balloon rise. A second third law pair is the force of gravity pulling down on the balloon from Earth, and the balloon also pulls upward on Earth with its own force of gravity.
The nail is applying the upward force to the hammer. The hammer applies a force to the nail, and the nail reflects this force back onto the hammer with an equal and opposite value.
Can't we explain why the third law doesn't forbid motion just by realizing that objects with different masses have different interias and hence different abilities to resist forces? So, if a bowling ball strikes bowling pins, isn't it more accurate to say that the bowling pins have less mass and so they can't resist as much force as the bowling ball can? Simply ignoring the opposite force excerted by the bowling pins might make calculations easier, but it doesn't actually explain what's going on.
The only thing wrong with your explanation is suggesting it is more accurate or more correct. If you want to broadly explain why the bowling pins get knocked out of the way while the bowling ball....well...bowls over them, your explanation is perfectly acceptable. If you want to know why the pins accelerated at the vectors and rates in which they did, you'd need to address the actual forces involved.
Worth watching just for the intro!! The bonus 4:30mins were also good. Well if I was this excited by it in my reaction, it goes without saying someone else had an equally disappointing reaction to it😒 Can't win em all Dave!!
This guy is amazing!! How did he know I was sitting on a chair?? Brilliant.
@Why so serious ? What is a toilet if not a poop chair?
Acknowledged
Mammoth Metal TV yeh ik he almost got me i’m sittting on a toilet doing my homework while i poop
You Design yoooo😂😂😂
HAHHAHHSAGSHAHA
I learn physics in my school just for exams....but I come on this channel just for my self....I understand concept physically.....very nice sir
There is an error at 1:21. The example given is not an action/reaction pair. (Gravity and Normal Force). The normal force can often be more or less then the gravitational pull on an object. For example, if you lean on a desk while sitting in your chair, the normal force from the chair will be less then your weight since some of the weight is held up by the desk. Action/reaction pairs are always equal in magnitude. The other clue here is action reaction pairs never act on the same system. The normal force from the chair is paired with the normal force from your body onto the chair. Two separate systems. Please either edit or have a floating comment as this is one of the most common misconceptions for students. Thanks.
Yes! Professor Dave - careful, the normal force and the gravity on the person are not a third law action-reaction pair. They are acting on the same body (the person). Third law action-reaction pairs act on different objects. The earth pulls on you and you pull up on the earth with the same force. The effects on each are very different. The pair from the normal on you (upwards) is the normal of your body on the chair (downwards).
since some of the weight is distributed then the normal is now equal to what ever remains on the chair and another on the desk
@@raulgracia9731 obvi
I have a different view on this. As you said when a body falls to the ground, it accelerates to ground and earth also accelerates a minuscule amount towards the falling object. Similiarly an action like a person jumping on the ground causes the earth to go down a minuscule amount since mass of earth is very high compared to the mass of the person. This is as per Newton’s III law of motion. In this example when you strike the hammer on nail, there are two different types of force on the nail. One is the normal gravitational force on the hammer. The other one is the downward force the striker exerts on the hammer . The normal gravitational force on the hammer has an effect on earth same as a body falls to the ground. When the striker forces the hammer down he is applying a force more than the gravitational force on hammer. In this case the force opposing the striking force as per the III law will be on the body of the striker . The body will go up a bit. If the striker stands on a weighing scale you will notice the scale dipping a bit.
u such a trash tryhard
Krish Dharury damnnnnn!!!!
Damn that's deep, didn't even think of that
Wow!!
"Professor Dave Explains!" *toooot* gets me every time.
Love that intro
Uh oh, the normal force on you from the chair is NOT the Newton's 3rd law "equal and opposite reaction" (counterforce) to your weight, even if it happens to be equal in magnitude and opposite in direction. Instead, the other member of the action-reaction pair is your gravitational pull up on the Earth. Action-reaction pairs (1) act on different objects and (2) must be of the same type!
This is the one thing keeping me from showing this video in my physics classes! I don't need my students to get confused that the normal force is a reaction force to the Earth pulling down on the person...
@@kimfermoyle1156 I thought that was the what the normal force was. What is it actually?
If the Earth pulling down on the person is the action force, the reaction force is the person pulling up on the Earth. An action-reaction pair is always two objects interacting with each other.
Professor Dave is a fantastic teacher, but thank you redbaron07, as soon as I saw that error, I went to the comments hoping someone would correct the good professor.
@@kimfermoyle1156 Yes same here. It is unfortunate.
Hi! I wound like to point out that in min 1:30 for me the video seems to imply that the normal force is the reaction of gravity .
That is not true. The reaction of gravity is gravity itself. And the reaction of the normal force is another normal force.
What happens is that while you are being pulled by earth ('s gravity), you encounter the earth's surface and your accelerated body pulls the ground down.
The ground returns the favour by pushing you up. That is the normal force.
To see that clearer, notice later in the video: the reaction never acts on the same body as the "original" force.
Therefore, normal force is not the reaction of gravity.
I thought the same exact thing. I think this is why the 3rd law gets confused so much. People think it's the normal force that is the reaction force but it's not. The last part in the video clears it up a little bit I think. Nice catch.
ok boomer
Covid infects me, I infect covid😂
Technically yes
@@MillerGut89 wha
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Sigma male octillianaire grindset
@@srithummalapalli3333 so true!
Online classes gang, where you at?
ong i can never learn from my physics teacher
@@melsalghul yep im sadly here to online school is really something
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1:18 this is NOT an example of a Newton's Third Law pair. both the Force of Gravity and the Normal Force are acting on the person sitting in the chair. Newton's Third Law requires two objects.
There are two objects, the person and the chair. The person applies a force to the chair, and the chair applies a force to the person.
The equal and opposite force is not between the hammer and the nail but rather, the source of the force, your arm, against the source of the opposite force which stops the force of your arm, the wood. Hope this helped!
So the force pair is between his arm and the wooden table?
Thanks Dave, You are the first one in five years to answer my question about how object can even move under the third law of motion. Hallelujah!
so clear and comprehensive, dave clearly knows the common misconceptions and misunderstandings of the third law. helped me clarify when the topic seemed so fuzzy i didn't know where to start or what to fix. thanks sm dave!
Thanks for the help Mr. Dave, your videos are fun and entertaining to watch, also, they teach me very well my lessons!
I hope you are doing well at this difficult times, and I wish you luck.
Excellent video professor Dave!.
hello appreciate the video. But I have one thing to clarify. The example you mentioned with the chair has a wrong part I guess. The third law states that every action force has an equal and opposite reaction force, BUT with the same TYPE. So the real reaction force to the gravitational force acting on the guy sitting on the chair is the gravitational force of the guy himself not the NORMAL force of the chair. Since the NORMAL force is not the same type of the GRAVITAIONAL Force. thanks for reading this and please correct me if I am wrong.
You're right. Normal force of chair on you and "normal force of you on chair" are a third law pair. "Earth pulls you" and "you pull Earth" are another third law pair. Just because two forces happen to be equal and opposite doesn't make them an action-reaction pair.
I literally asked my physics teacher today and she said what you just said haha. I’m only here cause I’m writing an physics exam tmrow
Hi Dave, what is the time span between the action and the reaction? (when your answer will be "none" then: is the force of the reaction when the first atom of an object (1) interacts with the first atom of another object (2) equal to the force of the reaction when the last atom of object 1 interacts with object 2?
This is why classical physics and quantum mechanics are two different fields of study at the moment.
Nice explanation professor
i always thought the 3 laws are best understood when learned in reverse order ... when students get to the first and final law, they are relieved that there is nothing happening to the object and no more equations to learn
I believe you. You really are the chemistry Jesus. Thank you
This is the physics section tho :/
Lol thought the same
So does the nail experience more acceleration than the hammer?
A=F/m, (the nail has more net force than the hammer). Like bowling ball and pin, if they both have equal and opposite forces, what net force moves pin away from the ball? Acceleration? A=F/m if F is equal on both objects, one with smaller mass will accelerate more than larger mass object.
when hammering a nail into a piece of wood the hammer imparts force on to the nail and the nail imparts force in to the hammer but the nail is drivin because there is a net force acting upon the nail from the motion of the hammer likewise the hammer has two forces upperating upon it the downwards force from your arm and the upward force from the nail that's why when you strike the nail, the hammers stops moving at roughly the location where the impact to curse so if we looking for the nail we only consider the forces acting at the nail if looking at the hammer we only consider the forces acting at the hammer
so helpful this helped me on homework
why is the bowling ball and bowling pin imparts equal force when the bowling ball has more mass and acceleration than the bowling pin?
ah, so the forces are equal, but because the bowling pin is more massive it experiences a much smaller change in acceleration, whereas the bowling pins are much lighter, so they experience a much greater change in acceleration.
"but because the bowling pin is more massive it experiences a much smaller change in acceleration" and then "whereas the bowling pins are much lighter, so they experience a much greater change in acceleration.
"?? explain please
DARK INFERNO i think he meant the bowling ball is more massive so the acceleration does not change as much as the bowling pins, which have less mass. This makes sense if both forces are equal and force equals mass times acceleration.
Uhhm did u Listen?
Let's suppose a body has mass of 5 kg and has velocity of 10 m/s...this body collides with another body of a bigger mass of 10 kg....but by law of conservation of momentum we know that product of mass and velocity of one body is equal to product of mass and velocity of another body if the two bodies undergo interaction....so the body with mass of 10 kg will experience a velocity of 5 m/s because of the law of conservation of momentum...
Same way the bowling ball has more mass than bowling pin but since they r in interaction, their product of m and a(acceleration) will be equal ,i.e, if bowling ball has more mass than bowling pin then bowling ball's acceleration must be smaller than bowling pin such that their forces are equal.
Thanks Sir Dave
Thank you Dave I didn’t understand how anything could move at all
I think the statement at 1:19 is incorrect as it suggests normal force and gravity are force pairs which I believe isn't the case. Please correct me if I'm wrong.
Oops spoke too soon there is already a comment about it that says the same thing.
So if I clasp my hands together, are there 2 forces (each hand pressing against each other, acting as force pairs for one another) or 4 forces (both hands pressing against each other, and the force pairs for both forces)
4. The net action and net reaction
Students beware, this video is clearly not well thought through. Anyone who knows a little bit of physics knows that 'these forces are equal so the car stops' at 1:05 and the so-called action-reaction pair example at 1:27 are serious misconceptions.
Thanks, Dave
I am Egyptian and I have to do a task on newton's laws, so because this video I can do it easily ❤
my dad and i we always watch this every day
thank you professor dave
What's the equal and opposite force of your hand in the hammer example?
What is the opposite reaction in the hammer and nail example.
Mistake???
I think relation between the gravity and the normal force does never never example of action and reaction.
How do you think about this ,Dave?
more correctly we can think of it as the normal force of the object on the earth and the normal force of the earth on the object, but yes this is how newton's third law works!
The force of gravity is an action force that is caused by the earth's gravity on the man. The reaction force would the be the force of gravity from the man acting on the earth. The normal force acting on the man is a separate force entirely. It would be paired with the normal force from the man on the chair.
For example: On ramps, the force of gravity points straight down toward the center of the earth, and the normal force is perpendicular to the ground, so at some angle. In this case, the normal force and gravity are both acting on the object but are not equal. Falling objects also have a force of gravity, but do not have a normal force.
In summary, the force of gravity and the normal force are independent of each other and do not cause one another, therefore they are not force pairs. (Though they each have a respective force pair.)
Another rule of this law is that the forces are acting on diferent objects. The gravity and the normal force are acting on the same object. This is not a good example.
you are totally right. it is a common misconception that the force of gravity and the normal reaction are considered as action and reaction! and no, professor dave, it is not how newton's third law works!
Because of u now i love science 🧪
Really sir you have cleared my all doubt 🤩, I have watched 10-11 videos but my doubts had not got cleared from them. Even my teacher didn't cleared my doubt😔
But you are awesome 🤩🤩🤩🤩
Can the third actually be explained by intertia? That, because an object will "want" to remain in its current state of motion, the normal force is just the object's resistance to a change in motion? Although, that would make the normal force a fictitous force, which doesn't seem right. Am I conflating two different things?
You are conflating two different things. The forces acting on the same object, adding up to zero, is Newton's first law, the law of inertia. Quantitatively, inertia is the m in Newton's second law, that is a body's resistance to accelerating. Newton's first law is a special case of Newton's second law, when the forces add up to zero.
The normal force is not a fictitious force. It is caused by outermost electron-electron repulsions, between two objects that are attempting to crash in to one another.
The two forces acting on two DIFFERENT objects, that are mirror images of each other, is Newton's 3rd law. This is the law that says that forces are a two way street. You cannot push without being pushed, you cannot touch without being touched. Earth pulls on you, and you pull on Earth. The only reason you move instead of the Earth, is that the Earth has a hell of a lot more mass, and doesn't move anywhere near the amount you do, when responding to the same magnitude of force.
This guy is brilliant he makes physics easy
Helped me dearly with my Science "Journey of a car" Homework. Thanks.
Sir action reaction forces should be same type of nature or not
Woww so amazing 😮😮😮😮😮
Well explained
EVERY ACTION HAS ITS EQUAL OPPOSITE REACTION
:-)
Have I found another Hamilton fan or are you just being a dork 😃
My question is, why did the planes on 9/11 sliced right through steel and reinforced concrete flooring without breaking a piece? Not to mention, that plane is way weaker than the tower. The plane literally flew inside the tower without damaging itself, this is impossible according to the 3rd law, right? To this day I’m very confused about hollow aluminum planes slicing steel.
Well, the notion that the plane flew inside the tower without damaging itself is pretty absurd. If it's going fast enough, anything could do massive damage. This should be common sense. You're only considering the materials, and entirely ignoring that one of those materials was going really fast. Do you expect it to just bounce off?
Willoughby Krenzteinburg
Look at the slow motion you won’t see a single piece breaking off. Two, wings and tail section would snap on an impact, yet it doesn’t do a single damage to the plane. Birds do more damage than steel and reinforced concrete. Nobody says it should bounce off, but you should at least see the debris falling when the plane impacted with the tower. Like I said, go watch it in slow motion and you literally see a plane slicing right through the towers.
@@moto__shark I've seen it, and you DO see debris falling. What is it you expect? An entire wing to fall intact after colliding into a building at 600 mph? It looks like exactly what a reasonably educated person would expect when a plane collides with a building at close to 600 mph. You're not adding anything new to your argument here, you realize that, right? Your counter is just "watch it again".
There are zero structural engineers or otherwise qualified experts who would endorse what you are saying.
Willoughby Krenzteinburg
600 mph? Planes cannot fly at such speed at low alt. Air density is too thick. Any educated person knows that commercial plane have turbine engines, not jet engines
@@moto__shark Good Lord.
Both planes were 767s which used jet engines. The first plane was going 494 mph. The second plane was going 586 mph. These speeds were analyzed using the footage available - which you clearly have access to. Denying this just makes you blindly and willfully ignorant; nothing more. There is absolutely no reason planes would be unable to reach these speeds. You're just literally making shit up as you go along, and are oblivious to how absurd it is.
What is it you are getting at anyway? Is your argument that they were not really planes....even though literally millions of people saw the second one as it was aired live - not to mention thousands in person? Is this what you are saying? Wasn't a plane?
Dear Professor Dave,
A parachutist with an open parachute. Could this be an example of Third Law? Many textbooks say no. I don't understand.
if it was a prime example of the third law then wouldn't the parachutist stay in place? perhaps that's why? ofc, everything could be an example of the third law but maybe it's not a prime one?
@@solomeen6512 Common misconception. Newton's third law pairs of forces do not both act on the same object.
There are N's 3rd laws involved for a skydiver, as the skydiver will cause a downwash of air, from the air applying the drag force to the parachute. You can feel a downwash of air from aircraft flying above you, which is the equal and opposite reaction to the air providing a lift force to the wings.
This is why the "birds in a truck" thought experiment, doesn't produce any lowering of weight of the truck as a whole. The birds flap their wings for a lift force, and the wings push downward on the air. The reaction to the wings pushing air down, is that air pushes the wings up. On net, a truck full of birds will still weigh the same, even if the birds fly inside instead of sit inside.
hi Dave, can you please explain the resultant of forces? i,j,k? tks
Resultant means the result of a vector math operation. In this case, it means the vector sum of the forces. Place the vectors tip-to-tail, and connect the first tip to the final tail, to find the vector sum of forces, i.e. net force.
The i/j/k refer to coordinate unit vectors, and have a hat like this: ^, written on top of them. I.e. vectors of magnitude of 1, that are used for keeping track of the components of vectors.
i is defined as the vector along the x-axis,
j is defined as the vector along the y-axis,
and k is defined as the vector along the z-axis.
If you are wondering why we use that particular trio of letters out of all possible letters, it has to do with Hamilton and quaternions. He came up with a concept that extended imaginary numbers in a way that could replace vectors in general. The three letters for the unit quaternions along each of the three axes, would all be a version of the sqrt(-1). What I call, the imaginary, joke, and kooky numbers. It didn't catch on to the extent he had wanted, but the notation still stuck. Some books use x-hat/y-hat/z-hat, instead of i-hat/j-hat/k-hat, to represent cartesian unit vectors.
Many thanks professor Dave
which pair of the following forces give zero resultant 2N and 2N
1N and 2N
2N and 2N
Thanks bro
Marvelous. But Sir what is torque?
i have a tutorial on that too, check it out!
There is another force on the nail by the wood called Fwood. Fhammer > Fwood forces the nail into the wood.
Farm is really confusing. It should be part of Fhammer and should not be added.
Prof Dave please correct your mistake on the normal force and weight being an action reaction pair. A lot of students are watching your videos which are very good so a correction would help them.
Light can break Newton's third law:
Wimmer, M., Regensburger, A., Bersch, C. et al. Optical diametric drive acceleration through action-reaction symmetry breaking. Nature Phys 9, 780-784 (2013). DOI: 10.1038/NPHYS2777
underrated comment
I don't understand, where does the force acting back on the original forcing body come from? Is it inertia?
It's just a truth. It's sort of like the object is "resisting".
I think you implied that the normal force of the chair was the reaction to the gravitational force pulling you down toward the center of the earth as you sit on the chair. The reaction would actually be your body pulling up on the earth's mass. I think that normal force is the force that is balancing the pull of gravity and putting the chair sitter in equilibrium -- a Newton's 1st law thing.
Gravity has not been determined whether it pulls or pushes, The jury is still out on this/.... as Newton and Einstein are not in agreement .. newton thinks it pulls down and Einstein is a fan of push.. to teach students that it is a pull when its not been settled is probably not fair.. these students will think they have the correct answer as the prof is the teacher... and the teacher is always right... hmmmm
Can you please explain why you consider it as a push @@alaskacanoe6837
Great stuff, thanks
When your here to watch the video for online class, but u constantly replay the the intro since it's so catchy
Teacher: State Newton's third law!
Me: Sir,You slapped me you got hurt!!!!
Moral of the story: Tit for Tat 🤣
Thank you
Excellent explanation sir😍
Thank you, Professor Dave!
The only good thing flat earthers have done is helping me to find this amazing channel 💙.
thank you professor
What happens when two hammers hammer each other at equal force? How do we determine the outcome ?
I was just thinking the same thing. But I’m still annoyed about the concept that for newtons 3rd law would seem to imply that no object could ever move, since any force accelerating an object must be paired with another in the opposite direction. For this reason we consider only the forces acting upon another object, and not the forces acting upon other objects. So if a person pushes a box we only consider the forces acting on the box. When looking at the person we only consider the force acting on the person. Okay, but this doesn’t ignore the fact the person is still experience a force the same amount of the box. That’s basically saying hey, just focus on what the objects are experiencing instead of worrying about why they are experiencing them. I find it odd that a person with less mass can push an object with more mass. That means the force the person with less mass applies to the box is great enough accelerate the larger mass. But if we look at the same force coming back at the person who has less mass the person isn’t being pushed backwards right? No. It’s odd that only the object being put into motion continues to be the object in motion.
@@ariel_12354as for the person pushing on the box. Yes it’s true that the force they push onto the box comes back to them. The reason the box moves is because it experiences enough force to overcome it’s maximum static friction with the floor, but the maximum static friction between your feet and the floor is higher, so you don’t slide back. It sounds weird because the box has more mass, but it’s due to the friction between the box snd the floor and your feet and the floor. Watch a video on static and kinetic friction
Well done Professor Dave!
Thank you very much professor!!! This video helps me so much solving my experiment task
every reaction is itself an action. also i havent read the book but i like the title. triumph of the man who acts.
thank you sir!
Hi Prof Dave, I love your videos and use them a lot in my classes. I would like to add one comment to this one though. Where you are explaining the force and counter-force acting on the sitting person, it is not exactly precise to state that the normal force is the counter-force of gravity. Gravity is the attractive force by the earth's mass on your body mass, thus the counter force to this would be your body mass attracting the earth vertically upwards. The normal force by the chair's surface on your butt has its pair as your butt is pushing against the chair -due to gravity. I would recommend this little change here, because to me what you have is a bit misleading. Force and counter force must act on different objects via an interaction. Gravity and the normal force are both acting on the sitting person, thus creating balance.
This is an EGREGIOUS error (as with 'these forces are equal so the car stops' at 1:05). To be honest, I can't imagine why these videos would be shown in any class if he has not addressed these mistakes in over a year.
You say the nail has the force of the arm/hammer acting on it, but what about the force of the wood pushing back on the nail?
sure, forces everywhere! we could start drawing vectors and never stop.
Thankyou
Very good
Im still confused, what if when two objects collide, both of them exert a force, so the 'action' has 2 forces, so does that mean there are 2 newton's third law, you know what i mean? Like from all the videos i have seen is always If Object 1 exerts a force on object 2, then object 2 exert a same and equal force on object 1, but what if when object 1 exerts a force, object 2 does it too
Thank you professor dave!
can somebody answer me this question :
horizontal acceleration : -9.8m/s^2, normal force = -gravity's force, gravity's force = m*a,
if so, is the normal force always increasing by the second? because gravity is increasing every second?
If the horizontal acceleration is -9.8 m/s^2, then this means that there is another force in addition to the object's weight, that is equal in magnitude to the object's weight acting on it to accelerate it sideways. And in the direction we assign as negative, traditionally west or south.
Given an acceleration that is exclusively horizontal, than this means vertical forces have to add up to zero. So some other force, like the normal force would be upward and equal in magnitude to gravity, so that vertical forces add up to zero.
In this example, it is just a coincidence that gravity would be equal in magnitude to m*a. Usually, that happens when the object is in free fall, rather than accelerating horizontally. Accelerating horizontally would require another kind of force to cause this acceleration.
Gravity is not increasing every second. Its speed could be increasing every second, but don't confuse speed increasing with gravity increasing.
Thanks. From Bangladesh.
If only I had seen this video when I first started learning about Newton's 3rd Law of Motion, it wouldn't have taken me 8 months to get comfortable with it.
By the way, I've heard a(n) (unsubstantiated) story that Newton had trouble with his 3rd Law, as well. Does anyone know if this was true?
Thank ya 😊
Give definition of newton's second law of motion
check my tutorial on that law
@@ProfessorDaveExplains sir give me link
The Third Law Pair with a person's weight is the force of gravity on planet earth from the person, not the normal force. What about freefall in that case? And force pairs never act on the same object!
Would the nail not experience an upward force from the wood when it is being hammered? Can someone please explain this to me.
Yes, it would. And then it breaks down to which is most able to resist the force applied, the hammer, the nail or the wood. This is also why, at some points, a nail bends instead of actually driving (deeper) into the wood.
Fantastic explanation of this theory. Thanks :)
The laws that are in FORCE by false entities cannot be binding because of the laws very own definition by use of word manipulation. This allows that law to mean one thing for one and different for another. Also one cannot be accountable for a law enFORCED as they are withheld from the people. Where as a commandment, if not covered or only apparent, allows one FREEDOM of will to make an informed morally based decision to obey
You're a little lost.
Great video
Sir can you please explain that what happens when we lift an object take for eg a chair so we apply a force on it in upward direction to lift then how does it apply a reaction force on our hands
When you a force upwards like lifting a chair the reaction is applied on the ground by your legs and ground should down in micro level. Something like jumping up and the force in the opposite direction is ground, which is small and not not noticeable.
Oh my days thank you soooooooo much
I was big time struggling this is amazing
Who is doing there online class
Thank you so much po, this really help me!!!♥️💕
Wait why does the bowling ball and the bowling pin exert the same force on each other if the bowling ball is heavier than the bowling pin?
Counterintuitive I know, but it's true! The confusion is rectified when you realize that F = ma applies. Same force, not the same mass so not the same acceleration.
Professor Dave Explains Oh ok. So do they have the same force because they’re a force pair and can’t have force on each other without the other?
One day, I’ll finally remember why the third law doesn’t imply that nothing should move, because of systems and because a=F/m . Until that day, I’ll keep coming back here like once a year I guess
can u pl explain the 3rd law more widely....its really confusing.....pl explain the hot air balloon concept with action reaction pair....
A hot air balloon rises, because there is a force of buoyancy that exceeds its weight. This is caused by an accumulation of air pressure that adds up (integrates) to exceed its weight, in response to it pushing its volume worth of air out of the way. The air pushes the balloon up, and the balloon pushes the air down. That is the Newton's third law pair involved in making a hot air balloon rise. A second third law pair is the force of gravity pulling down on the balloon from Earth, and the balloon also pulls upward on Earth with its own force of gravity.
Love the tat Professor Dave
I love you professor dave
Bowling ball imparts more force
Acceleration is more in bowling pin
I’m having a hard time understanding and imagining the blue vector
How is the nail having an upward force? For some reason I just can’t get it
The nail is applying the upward force to the hammer.
The hammer applies a force to the nail, and the nail reflects this force back onto the hammer with an equal and opposite value.
good video
Absolutely amazing! Very well done! Thank you!
Can't we explain why the third law doesn't forbid motion just by realizing that objects with different masses have different interias and hence different abilities to resist forces? So, if a bowling ball strikes bowling pins, isn't it more accurate to say that the bowling pins have less mass and so they can't resist as much force as the bowling ball can? Simply ignoring the opposite force excerted by the bowling pins might make calculations easier, but it doesn't actually explain what's going on.
The only thing wrong with your explanation is suggesting it is more accurate or more correct. If you want to broadly explain why the bowling pins get knocked out of the way while the bowling ball....well...bowls over them, your explanation is perfectly acceptable. If you want to know why the pins accelerated at the vectors and rates in which they did, you'd need to address the actual forces involved.
Worth watching just for the intro!! The bonus 4:30mins were also good. Well if I was this excited by it in my reaction, it goes without saying someone else had an equally disappointing reaction to it😒 Can't win em all Dave!!
Normal force and gravitational force are not an action reaction pair. They’re both forces that act on YOU