Sir, you explained very beautifully. that show how great person you are. I really appreciate you taking time off from your busy life and teaching us these complex ideas and explaining them so easily. that even a dumb guy like me can understand. Bundle of Thanks.
This video is amazing. IT WAS EXACTLY WHAT I WAS LOOKING FOR to understand this concept. You really opened my mind about this concept. I love the way you teach, your interaction with students. Everything makes it so interesting. After this video i actually like physics more hehe.I wish you were my Professor.
Wow,u make physics so fun and practical.Teachers like u are what students need to fall in love with learning and physics.Grrreat video,pls keep up the good work :D :D
pavan, Very flattering, and very untrue. But thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A
Professor, Thanks a lot for this lucid explanation. My query is that, will this conservation of momentum hold true for a launch vehicle with in the earth’s atmosphere? Will it be correct to say that the stage separation of the rockets occur in order to reduce its mass as per the equation?
what if the person throwing the wrench throws it using a battery powered wrench thrower and has a rope tied to the wrench, then after throwing, stops the wrench and slowly pulls it back to himself. When he has the wrench in his hands will the whole system have moved in an opposite direction of the throw?
Clorox Bleach #1, Exactly. And love the username. Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A
If you do reply my questioon is if something has a M=5kg which means 49N needed for thrust does how many times the needed N=there M/s like so does 147N mean it would go 2-3M/s 3if you account the needed intial force.
Is the final momentum was additive in nature by considering the direction ? 1)P = mv +MV or 2)P = mv- MV Because some books consider 1st one for solving rocket equation.
Sourav Kumar Nath, Depends on your frame of reference (earth or rocket) and also which way you regard the velocity of the exhaust. Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A
Great explanation for the concepts presented but as a beginning physics student it leaves me wondering... At time 0, the astronaut and the ISS are orbiting the earth. When her tether breaks, the astronaut immediately throws the wrench. Assuming she throws it in a straight line from the release point, doesn't this propel her in a straight line back toward the ISS -- which will have moved on by the time she reaches its former position?
You are correct that things get a bit more complicated when in orbit, and particularly if they are separated by a good distance. I guess here we're assuming no effects due to being in orbit. Cheers, Dr. A
Thanks Yahya, The minus sign indicates movement to the left (if we're calling movement to the right positive). If Vp is speed (a scalar, hence a positive number), you put the minus sign out in front to indicate a negative velocity. (Alternately, if you kept all the velocities as vectors, you would use the plus sign, but the Vp velocity vector would be a negative number, and you'd get the same result). Cheers, Dr. A
“Decrease your mass to move faster”. Me: *shits myself during panic attack* that works 😅👍🏽 In practice, the ISS is experiencing circular motion, so unless you plan the maneuver proper, you could miss the station and start floating out into space. That said, this was a very instructive example!
Float Circuit, Hilarious, love it. Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A
The gasses are essentially "exploding" inside the rocket, and the only exhaust path is out the back. Thus they shoot out with very high velocity. Cheers, Dr. A
I get the concept, but I struggle with grasping the practicality of this situation. If space is a vacuum, or there is no air and no pressure in space, what produces the opposite reaction to force your momentum in the opposite direction? Wouldn't the conservation of momentum in space force both you and the wrench to continue in the wrong direction? Or would the reaction between you and the wrench be enough?
"What produces the opposite reaction to force your momentum in the opposite direction?" -- Think of Newton's second law. "The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed." Here the motive force is the wrench you're throwing. When you throw it, think of that as a push, which is a force. Now Newton's third law. "To every action there is always opposed an equal reaction; or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts." Therefore when you push the wrench it pushes back on you. I'm not sure what you mean by the second and third questions. To continue the simplicity of the problem, as long as you throw the wrench in the opposite direction of the ISS then you will get back to the station.
You're over thinking it. It depends which part of space you're talking about, how fast its expanding, it depends on your speed on your way back to the ISS and not the wrenches. Something would have to be effecting that small amount of space between you and the station. If the space effects you AND the station the same (like a gravity wave passing through) then it wouldn't matter and you wouldn't notice any change in distance.
You are making the common mistake of assuming the wrench (or rocket exhaust) is "pushing" on the air around us. And that without that air up in space, there is nothing to push on at all. But it doesn't work like that. It's a very common misconception. Like Christopher Smith said, for every action there is an equal and opposite reaction. You throw the wrench one way, you go the other way. It has nothing to do with the air, or lack of air.
Great video, the class is really engaging, makes the student enjoy it. However, I have one question, Dr. Anderson. I apologize in advance for the lengthy message, but I think it’s necessary. I totally understand the conservation of momentum in situations like a person pushing another one on an ice ring; or an astronaut throwing a wrench in an attempt to get back to the ISS (by the way, if we had molecules of gases on space, we should be able to move just by kicking the air, because we would be exerting a force on the molecules, and the molecules on us, right? That's just a hypothetical situation). The thing is, I don't really understand the conservation of momentum when the system involves gases(explosions, propulsion of a rocket,etc). For example, if a have a big stone, stationary, then I put an explosive in a hole inside the stone. And let's assume that the stone breaks into 2 chunks, that gains momentum in a straight line only (the X-axis). Conservation of momentum says that the momentum applied by the gases at the chunk that moves to the right and at the one that moves to the left has the same magnitude but opposite direction. But how does that work? I mean, when I push someone on an ice ring, I apply a force on that person, and he/she on me, as a reaction. But how does that applies to gases of the explosive? Part of the gases apply a force to the chunk moving to the right, during a dt, which results in a quantity of momentum to the right(and the reaction force is the one that the chunk applies to the gases), and another part of the gases apply a force to the chunk that moves to the left, during a dt, which results in a momentum that has the exactly same magnitude of that momentum applied to the chunk that moves rightward, how crazy is that? I mean, am I thinking too much about it? I do not see my peers thinking this way(like, they do not talk about the gases of the explosive and etc) and it really frustrates me at times, because I am spending way more time than my peers studying this subject. Again, great class! Cheers from Brazil!
Gabriel - If I had a catapult in space that fired blocks of water ICE, would the catapult feel a recoil force when it fires the block? YES Now what about a tank full of LIQUID water of the same mass as the ice block? Now how about a FIREHOSE in space? Would a person hold a firehose feel the recoil when the water shoots out into space? YES. Now what if the water was a GAS (super heated steam) but of the SAME MASS? Will the firehose feel recoil if the water is superheated as it comes out? Hint: WATER VAPOR (gaseous water) STILL HAS MASS.
@@stuartgray5877 Thank you, Stuart! It's becoming clearer. But still, thinking about the water in hose. Think that we have a reservoir up in the air, and a hose connected to it. So we do not use any pump, we just let gravity do its job. So, water is being shot out by the GRAVITY FORCE, and the reaction force to this force g force that is acting upon the water is the FORCE that WATER EXERTS ON THE EARTH'S CENTER. So, we have the action-reaction pair. So, Mr Stuart, If we look at it, we do not see any FORCE ACTING UPON THE HOSE itself, so how does the hose goes backwards??? I mean, when I throw something, this something applies a force on me, that explains why I go backwards. But, in the HOSE case, why does it go backwards if nothing is applying a force on it?
@@gabrieldecker7209 WHY are you confusing the problem with a gravity fed water canon? Lets just talk about a water canon that expels the water at 3000 PSI. Would a person holding this water canon IN SPACE, feel a recoil when the water shoots out at 3000 PSI? have you EVER seen a video of firemen trying to hold on to a firehose alone? Maybe you should look that up?
Stuart Gray I must lack knowledge, it seems simple to you, but I’m kinda struggling, idk why... Mr Stuart, see if I’m thinking correctly about the spacecraft. When it is blowing gases backwards, it goes forward. But the thing is, like I said before, if I throw a wrench, the wrench “throws” me, and that’s why I move, bc sth is acting upon me. So, when the spacecraft blows gas backwards, it moves forward because the gases are exerting forces IN SOME PART(i don’t know which part) of this spacecraft, is that right sir? Besides, this part of the spacecraft where the gases are exerting force upon must be one of the strongest parts. Is that right, Mr Stuart?
@@gabrieldecker7209 The thing that gets the force applied to it is the Rocket Nozzle. Large Rocket engines have a giant nozzle that can expel massive quantities of gases at supersonic speed. The gases MUST have a force applied to them to be accelerated. The force is from the nozzle and the components in the engine that accelerate the fluids into the combustion chamber. On smaller spacecraft (like deep space probes) the engines are much smaller and mix Bi-propellants or mono-propellants to create thrust. Some thrusters I have had experience with were so small we called them "mouse farts" and were used to change the pointing of a spacecraft.
Conservation of momentum always works (as long as you identify the entire system of particles). It works in collisions but also in explosions. A rocket exhaust is sort of like a controlled explosion. The gas that expanded rapidly not only pushed itself out of the rocket, but also pushed the rocket forward. Cheers, Dr. A
I love science, but seriously struggle with algebra... Yet every thing you just said made perfect sense straight away, I wish you could have been my science teacher👌
Sorry to hear that. Hopefully my channel will help a bit. I would suggest getting a study group together. See my video here: ruclips.net/video/4oW3tWAylpw/видео.html Cheers, Dr. A
CLEARLY, gravity AND ELECTROMAGNETISM/energy are linked AND BALANCED opposites (ON BALANCE); as the stars AND PLANETS are POINTS in the night sky. Consider TIME (AND time dilation) ON BALANCE. By Frank DiMeglio
but.. you could engage in some FLATULENCE and use that to Propel yourself toward the Space station!!.. lol, okay, that was Sophomoric but SOMEBODY had to say that!!.. (nevermind that I'm 65 years old and saying it... )
John Sumner, Yep. Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A
@@yoprofmatt in that case why not draw a free body diagram illustrating the force pairs the rocket needs to create in order to produce motion? that's what a real teacher would do imo.
@@papalegba6759 - "in that case why not draw a free body diagram" Coming from someone that REFUSES to provide this free body diagram even though I have been ASKING FOR YEARS - LITERALLY! So shut the fuck up!
Excellent question. Here we are talking about one impulse: we throw one object, and then we recoil. With a rocket, however, there is a continuous stream of particles being thrown out the back (the exhaust). Momentum changes continuously over time. Remember that F = ma = dP/dt, so herein lies your acceleration. Also note that the "exact" calculation for rocket propulsion gets a bit tricky. I'll try to make another video soon laying out the full details. Cheers, Dr. A
pretty sure a rocket is a heat engine of the internal combustion type, and thus dependent upon doing PV work. so i have no idea why you're blabbing about conservation of momentum and people throwing spanners in space.
pretty sure you are a high school dropout that has never taken a single physics class in your life. STOP trying to lecture actual engineers about basic physics. All you do is make a fool of yourself
All of the explanations of rocket propulsion I've seen on RUclips invoke Newton's third law of motion or use conservation of momentum. The third law of motion states that if two bodies INTERACT then the force exerted by body A will be equal and opposite to the force body B exerts back on body A. It is incorrect to say that the gas exiting the rocket in the backward direction causes the rocket to move in the forward direction, by Newton's third law, because there is no INTERACTION between the exiting gas and the rocket. The law of conservation of momentum is not a law like Newton's second law of motion which states that if there is a net, non-zero force on a body then the body will accelerate in the direction of the net force and is always true. The law of conservation of momentum is derived from Newton's second law and is true only in certain restricted cases. If you have a system of interacting bodies, they must obey Newton's third law in pairs so that all the internal forces between the bodies add to zero. Second, the sum of the external forces acting on the bodies must also add to zero. If these two conditions are met, then the total momentum of the system of bodies will be conserved. A rocket leaving the surface of the Earth doesn't obey the conservation of momentum because gravity is an external force acting on the rocket. Only if the rocket is in outer space, far from any gravitating bodies, can the conservation of momentum be applied. So, how can you provide a simple explanation for rocket motion? I believe that all you need to say is that the hot gases entering the exhaust chamber of the rocket expand in all directions and that the part of the gas having a forward component of velocity pushes the rocket forward. It can be said that calculating the change in a rocket's velocity is difficult in a gravity field and conservation of momentum can be used in the simple case of no external forces.
Sir, you explained very beautifully. that show how great person you are. I really appreciate you taking time off from your busy life and teaching us these complex ideas and explaining them so easily. that even a dumb guy like me can understand. Bundle of Thanks.
You're very welcome. Thanks for commenting, and keep up with the physics (or maybe the boxing as your username suggests?).
Cheers,
Dr. A
You are a wonderful human being that the world is lucky to have. I wish you were my professor. *sigh*
+Kraetos John
Now this comment makes me feel very loved. Thanks very much.
Cheers, Dr. A
I’m a young guy and Im a big fan of astrophysics I loveeee videos about rockets and space thank you so much for this video🙂
Nayef Alhajraf,
You're very welcome. Glad you're enjoying the videos.
You might also like my new site: www.universityphysics.education
Cheers,
Dr. A
I just can't believe, how talented teachers are there in this world. You made me your fan.
Rocket Scientist you say? *scoffs* That's just conservation of momentum!
BEST PHYSICS LECTURES EVER !!!
Prof i like how you teach physics, you actually teach physics whilst solving real world problems and i think that makes your lectures very cool.
Excellent explanation. We need more teachers and professors like this gentleman.
Thanks for the comment. Hope you're enjoying the physics.
Cheers,
Dr. A
This video is amazing. IT WAS EXACTLY WHAT I WAS LOOKING FOR to understand this concept. You really opened my mind about this concept. I love the way you teach, your interaction with students. Everything makes it so interesting. After this video i actually like physics more hehe.I wish you were my Professor.
God level of teaching !
I like the explanation this is particularly good for revising something you have already learnt about
+Iron Phoenix Thanks much Iron Phoenix (best name ever).
Cheers, Dr. A
Wow,u make physics so fun and practical.Teachers like u are what students need to fall in love with learning and physics.Grrreat video,pls keep up the good work :D :D
Great to hear. I'm always trying to improve the delivery. Stay tuned.
Cheers,
Dr. A
Your are a real genius nothing can compare u
pavan,
Very flattering, and very untrue.
But thanks for the comment, and keep up with the physics!
You might also like my new website: www.universityphysics.education
Cheers,
Dr. A
Sir ever amazing lecture regarding the same topic
I got it very well
THIS WAS SO GOOD
u r grt and i think very talented also.....thnx a lottt
You are an amazing teacher
Thanks a lot for these video's they are very helpful
Good to hear. Glad they're useful. Keep up with the physics.
Cheers,
Dr. a
Thank you sir for your clear explanation
Thank you very much for this explanation
You bet. Thanks for the shout out.
Cheers,
Dr. A
thanks, great explanation.
+Durin's Bane Cheers! Dr. A
What a great explanation thanx 😊
You are very welcome. Thanks for tuning in.
Cheers,
Dr. A
Very nicely explained!
Thanks for watching!
Cheers,
Dr. A
Its great .simply cleared .
Clear is good.
Cheers,
Dr. A
Thank you so much Sir,I have an entrance exam for an amazing university coming up and I need ace it !!
Best of luck to you. Be amazing.
Cheers,
Dr. A
Professor, Thanks a lot for this lucid explanation. My query is that, will this conservation of momentum hold true for a launch vehicle with in the earth’s atmosphere? Will it be correct to say that the stage separation of the rockets occur in order to reduce its mass as per the equation?
Thank you
Omar Elmoré,
You're very welcome. Glad you're enjoying the videos.
You might also like my new site: www.universityphysics.education
Cheers,
Dr. A
what if the person throwing the wrench throws it using a battery powered wrench thrower and has a rope tied to the wrench, then after throwing, stops the wrench and slowly pulls it back to himself. When he has the wrench in his hands will the whole system have moved in an opposite direction of the throw?
Great explanation. Can we think of the empty rocket as the person and the wrench as the fuel?
Clorox Bleach #1,
Exactly. And love the username.
Thanks for the comment, and keep up with the physics!
You might also like my new website: www.universityphysics.education
Cheers,
Dr. A
If you do reply my questioon is if something has a M=5kg which means 49N needed for thrust does how many times the needed N=there M/s like so does 147N mean it would go 2-3M/s 3if you account the needed intial force.
Is the final momentum was additive in nature by considering the direction ?
1)P = mv +MV or 2)P = mv- MV
Because some books consider 1st one for solving rocket equation.
Sourav Kumar Nath,
Depends on your frame of reference (earth or rocket) and also which way you regard the velocity of the exhaust.
Thanks for the comment, and keep up with the physics!
You might also like my new website: www.universityphysics.education
Cheers,
Dr. A
thanks
this is such a great video!! wonderfully explained. well done Alex.half of the time i was wondering what it was that you were writing on. :p
+Arshmah Siddiqui Check out the board here: learningglasssolutions.com
Cheers, Dr. A
Beautiful example...
Thank you. Oldie but goodie.
Cheers,
Dr. A
Great explanation for the concepts presented but as a beginning physics student it leaves me wondering... At time 0, the astronaut and the ISS are orbiting the earth. When her tether breaks, the astronaut immediately throws the wrench. Assuming she throws it in a straight line from the release point, doesn't this propel her in a straight line back toward the ISS -- which will have moved on by the time she reaches its former position?
You are correct that things get a bit more complicated when in orbit, and particularly if they are separated by a good distance. I guess here we're assuming no effects due to being in orbit.
Cheers,
Dr. A
Great explanation . Well done sir .
But why is the Pf =MwVw-MpVp
Isn't supposed to be + in between ?
Thanks Yahya,
The minus sign indicates movement to the left (if we're calling movement to the right positive). If Vp is speed (a scalar, hence a positive number), you put the minus sign out in front to indicate a negative velocity. (Alternately, if you kept all the velocities as vectors, you would use the plus sign, but the Vp velocity vector would be a negative number, and you'd get the same result).
Cheers,
Dr. A
“Decrease your mass to move faster”. Me: *shits myself during panic attack* that works 😅👍🏽
In practice, the ISS is experiencing circular motion, so unless you plan the maneuver proper, you could miss the station and start floating out into space. That said, this was a very instructive example!
Float Circuit,
Hilarious, love it.
Thanks for the comment, and keep up with the physics!
You might also like my new website: www.universityphysics.education
Cheers,
Dr. A
Dr. A i have a question
Does the gasses move with a velocity relative to the rocket???? if so Why?????
The gasses are essentially "exploding" inside the rocket, and the only exhaust path is out the back. Thus they shoot out with very high velocity.
Cheers,
Dr. A
haha lets get it ! i love physics
Music to my ears.
Cheers,
Dr. A
I get the concept, but I struggle with grasping the practicality of this situation. If space is a vacuum, or there is no air and no pressure in space, what produces the opposite reaction to force your momentum in the opposite direction? Wouldn't the conservation of momentum in space force both you and the wrench to continue in the wrong direction? Or would the reaction between you and the wrench be enough?
Or if space is expanding at a velocity faster than I can throw the wrench, wouldn't that cause a problem too? Or am I overthinking it?
"What produces the opposite reaction to force your momentum in the opposite direction?" -- Think of Newton's second law. "The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed." Here the motive force is the wrench you're throwing. When you throw it, think of that as a push, which is a force. Now Newton's third law. "To every action there is always opposed an equal reaction; or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts." Therefore when you push the wrench it pushes back on you. I'm not sure what you mean by the second and third questions. To continue the simplicity of the problem, as long as you throw the wrench in the opposite direction of the ISS then you will get back to the station.
You're over thinking it. It depends which part of space you're talking about, how fast its expanding, it depends on your speed on your way back to the ISS and not the wrenches. Something would have to be effecting that small amount of space between you and the station. If the space effects you AND the station the same (like a gravity wave passing through) then it wouldn't matter and you wouldn't notice any change in distance.
You are making the common mistake of assuming the wrench (or rocket exhaust) is "pushing" on the air around us. And that without that air up in space, there is nothing to push on at all. But it doesn't work like that. It's a very common misconception. Like Christopher Smith said, for every action there is an equal and opposite reaction. You throw the wrench one way, you go the other way. It has nothing to do with the air, or lack of air.
Thanks
You are welcome. Keep up with the physics.
Cheers,
Dr. A
Great video, the class is really engaging, makes the student enjoy it. However, I have one question, Dr. Anderson. I apologize in advance for the lengthy message, but I think it’s necessary. I totally understand the conservation of momentum in situations like a person pushing another one on an ice ring; or an astronaut throwing a wrench in an attempt to get back to the ISS (by the way, if we had molecules of gases on space, we should be able to move just by kicking the air, because we would be exerting a force on the molecules, and the molecules on us, right? That's just a hypothetical situation). The thing is, I don't really understand the conservation of momentum when the system involves gases(explosions, propulsion of a rocket,etc). For example, if a have a big stone, stationary, then I put an explosive in a hole inside the stone. And let's assume that the stone breaks into 2 chunks, that gains momentum in a straight line only (the X-axis). Conservation of momentum says that the momentum applied by the gases at the chunk that moves to the right and at the one that moves to the left has the same magnitude but opposite direction. But how does that work? I mean, when I push someone on an ice ring, I apply a force on that person, and he/she on me, as a reaction. But how does that applies to gases of the explosive? Part of the gases apply a force to the chunk moving to the right, during a dt, which results in a quantity of momentum to the right(and the reaction force is the one that the chunk applies to the gases), and another part of the gases apply a force to the chunk that moves to the left, during a dt, which results in a momentum that has the exactly same magnitude of that momentum applied to the chunk that moves rightward, how crazy is that? I mean, am I thinking too much about it? I do not see my peers thinking this way(like, they do not talk about the gases of the explosive and etc) and it really frustrates me at times, because I am spending way more time than my peers studying this subject.
Again, great class! Cheers from Brazil!
Gabriel - If I had a catapult in space that fired blocks of water ICE, would the catapult feel a recoil force when it fires the block? YES
Now what about a tank full of LIQUID water of the same mass as the ice block?
Now how about a FIREHOSE in space? Would a person hold a firehose feel the recoil when the water shoots out into space? YES.
Now what if the water was a GAS (super heated steam) but of the SAME MASS?
Will the firehose feel recoil if the water is superheated as it comes out?
Hint: WATER VAPOR (gaseous water) STILL HAS MASS.
@@stuartgray5877 Thank you, Stuart! It's becoming clearer. But still, thinking about the water in hose. Think that we have a reservoir up in the air, and a hose connected to it. So we do not use any pump, we just let gravity do its job. So, water is being shot out by the GRAVITY FORCE, and the reaction force to this force g force that is acting upon the water is the FORCE that WATER EXERTS ON THE EARTH'S CENTER. So, we have the action-reaction pair. So, Mr Stuart, If we look at it, we do not see any FORCE ACTING UPON THE HOSE itself, so how does the hose goes backwards??? I mean, when I throw something, this something applies a force on me, that explains why I go backwards. But, in the HOSE case, why does it go backwards if nothing is applying a force on it?
@@gabrieldecker7209 WHY are you confusing the problem with a gravity fed water canon?
Lets just talk about a water canon that expels the water at 3000 PSI.
Would a person holding this water canon IN SPACE, feel a recoil when the water shoots out at 3000 PSI?
have you EVER seen a video of firemen trying to hold on to a firehose alone?
Maybe you should look that up?
Stuart Gray I must lack knowledge, it seems simple to you, but I’m kinda struggling, idk why... Mr Stuart, see if I’m thinking correctly about the spacecraft.
When it is blowing gases backwards, it goes forward. But the thing is, like I said before, if I throw a wrench, the wrench “throws” me, and that’s why I move, bc sth is acting upon me. So, when the spacecraft blows gas backwards, it moves forward because the gases are exerting forces IN SOME PART(i don’t know which part) of this spacecraft, is that right sir? Besides, this part of the spacecraft where the gases are exerting force upon must be one of the strongest parts.
Is that right, Mr Stuart?
@@gabrieldecker7209 The thing that gets the force applied to it is the Rocket Nozzle.
Large Rocket engines have a giant nozzle that can expel massive quantities of gases at supersonic speed. The gases MUST have a force applied to them to be accelerated. The force is from the nozzle and the components in the engine that accelerate the fluids into the combustion chamber.
On smaller spacecraft (like deep space probes) the engines are much smaller and mix Bi-propellants or mono-propellants to create thrust.
Some thrusters I have had experience with were so small we called them "mouse farts" and were used to change the pointing of a spacecraft.
Conservation of momentum is valid when there is collision but.. What about rocket 🚀. One there is no collision between the particles exhausted out?
Conservation of momentum always works (as long as you identify the entire system of particles). It works in collisions but also in explosions. A rocket exhaust is sort of like a controlled explosion. The gas that expanded rapidly not only pushed itself out of the rocket, but also pushed the rocket forward.
Cheers,
Dr. A
@@yoprofmatt so COM is defined as m1*v1=m1*v1? news to me. also pretty sure a CD nozzle doesn't 'push' a gas, but meh...
Ok. This means Law of conservation of momentum is same as Third law of motion. Right?
Precisely. When newton originally proposed his 3rd law of motion he proposed it in the form of conservation of momentum.
Where do they write on?
Does he write backwards?
+Onur Gücükoğlu Onur, no I just do a horizontal "flip" of the image.
Cheers, Dr. A
no wonder why your wedding ring is in your right hand. lol
What about students in attendance? Do they watch what's written backwards?
I am not a degree holder but I can understand.
you're cool
What's that board on which u write called
+Asd Fgh
It's called Learning Glass. You can see more here: learningglasssolutions.com
Cheers, Dr. A
I love science, but seriously struggle with algebra... Yet every thing you just said made perfect sense straight away, I wish you could have been my science teacher👌
Thanks Harry,
Math (and physics) takes time to master. Keep working on both, put in the time, and you'll get it.
Cheers,
Dr. A
You know Dr. Anderson. I love physics so much yet I do not understand even a single concept in it. I feel like my mind is blocked.
Sorry to hear that. Hopefully my channel will help a bit. I would suggest getting a study group together. See my video here: ruclips.net/video/4oW3tWAylpw/видео.html
Cheers,
Dr. A
What are the odds! My names Alex!
Odds are probably pretty good. This video has 12k views, so there was bound to be an Alex eventually.
Cheers,
Dr. A
Matt Anderson Fair point :)
Great video as well. Very clear even to a 16 year old
CLEARLY, gravity AND ELECTROMAGNETISM/energy are linked AND BALANCED opposites (ON BALANCE); as the stars AND PLANETS are POINTS in the night sky.
Consider TIME (AND time dilation) ON BALANCE.
By Frank DiMeglio
but.. you could engage in some FLATULENCE and use that to Propel yourself toward the Space station!!.. lol, okay, that was Sophomoric but SOMEBODY had to say that!!.. (nevermind that I'm 65 years old and saying it... )
Yes
Cool beans.
Dr. A
Is this also an example of Newton's third Law ?
John Sumner,
Yep.
Thanks for the comment, and keep up with the physics!
You might also like my new website: www.universityphysics.education
Cheers,
Dr. A
@@yoprofmatt in that case why not draw a free body diagram illustrating the force pairs the rocket needs to create in order to produce motion? that's what a real teacher would do imo.
@@papalegba6759 - "in that case why not draw a free body diagram"
Coming from someone that REFUSES to provide this free body diagram even though I have been ASKING FOR YEARS - LITERALLY!
So shut the fuck up!
Benedict Cumberbatch anyone?
Quite a few of my students agree with you. Now if only I could act!
Cheers,
Dr. A
where is rocket acceleration?????
Excellent question. Here we are talking about one impulse: we throw one object, and then we recoil. With a rocket, however, there is a continuous stream of particles being thrown out the back (the exhaust). Momentum changes continuously over time. Remember that F = ma = dP/dt, so herein lies your acceleration. Also note that the "exact" calculation for rocket propulsion gets a bit tricky. I'll try to make another video soon laying out the full details.
Cheers,
Dr. A
pretty sure a rocket is a heat engine of the internal combustion type, and thus dependent upon doing PV work. so i have no idea why you're blabbing about conservation of momentum and people throwing spanners in space.
pretty sure you are a high school dropout that has never taken a single physics class in your life.
STOP trying to lecture actual engineers about basic physics.
All you do is make a fool of yourself
@@stuartgray5877 pretty sure any "engineer" that doesn't know a rocket is a heat engine is useless lol.
Why not just use your SAFER device to propel yourself back to the ISS?
All of the explanations of rocket propulsion I've seen on RUclips invoke Newton's third law of motion or use conservation of momentum. The third law of motion states that if two bodies INTERACT then the force exerted by body A will be equal and opposite to the force body B exerts back on body A. It is incorrect to say that the gas exiting the rocket in the backward direction causes the rocket to move in the forward direction, by Newton's third law, because there is no INTERACTION between the exiting gas and the rocket.
The law of conservation of momentum is not a law like Newton's second law of motion which states that if there is a net, non-zero force on a body then the body will accelerate in the direction of the net force and is always true. The law of conservation of momentum is derived from Newton's second law and is true only in certain restricted cases. If you have a system of interacting bodies, they must obey Newton's third law in pairs so that all the internal forces between the bodies add to zero. Second, the sum of the external forces acting on the bodies must also add to zero. If these two conditions are met, then the total momentum of the system of bodies will be conserved. A rocket leaving the surface of the Earth doesn't obey the conservation of momentum because gravity is an external force acting on the rocket. Only if the rocket is in outer space, far from any gravitating bodies, can the conservation of momentum be applied.
So, how can you provide a simple explanation for rocket motion? I believe that all you need to say is that the hot gases entering the exhaust chamber of the rocket expand in all directions and that the part of the gas having a forward component of velocity pushes the rocket forward. It can be said that calculating the change in a rocket's velocity is difficult in a gravity field and conservation of momentum can be used in the simple case of no external forces.