These video's are amazingly helpful. Just started biomechanics and some of these concepts are impossible to understand in written form. I dunno who this guy is but he's definitely got a talent for teaching this stuff.
i guess im asking the wrong place but does anybody know of a method to get back into an Instagram account? I was stupid lost my password. I love any help you can give me.
the downward acceleration due to gravity is positive ..... the upward acceleration is negative bcz its decreasing and to downward its increasing .... so simple
In fact, it doesn't matter wether you say it's positive or negative, but it has to make sense according to the other variables. For example, if height is greater as it grows upwards, so is gravitity.
It depends on what you consider to be the positive direction. Is it upward or downward? You have to adjust the sign of your variables accordingly to that direction (because we're dealing with vector quantities). If it is upward, then: a = -9.8 m/s^2, otherwise it is: a = 9.8 m/s^2
@MrBaniboy Because it happens on so many videos that someone says: it's much easier that other way or the way you showed is wrong/complicated. The videos are NOT meant to be the best/easiest/whatever solution to a problem. Videos Sal makes belong to a series. They almost all have. Every video expands the concepts of the previous. If you bothered to check this series contents, it's about Newton's laws of motion, motion and acceleration.
if you plug in al the values you just mentioned you can see its the same thing he wrote. but if you just think of it as the magnitude quantity of gravity and not as an acceleration vector you might forget to put the sign
If we take the direction of motion of the ball as the positive sense, then all variables will be positive, so as the acceleration due to gravity since the ball will accelerate faster and faster as it moves down before it hits the ground. In this case it would make sense how we arrive at: 2*(9.8)*h = v^2 following the formula: 2as = v^2 I think if we take the direction of motion of the object as the positive sense, intuition will come much faster. Great vid Sir Sal! Sir Mahesh also explained this very well on Khan Academy India English!
I was wondering if you would be able to explain to me when calculating velocity regarding energy conservation we use v=(square root) (2gh) but when calculating velocity normally we can use v=delta distance / delta time.
What are you talking about? There's no reason why it shouldn't be said that downward acceleration is negative. It's just a convention. If you don't understand that, then you're "not so intellegent", and don't you EVER say that about Sal.
Good stuff Khan. My only recommendation is...always use the sign convention only for accelerations and velocities. Never for distances. This way the formula will naturally tell you if the final velocity is negative or positive without imposing for instance a "negative squared root". Thanks.
Your method is very weird. Why not simply use the equation to solve the potential energy of the rock first ( E = m * h * 9.81 m/s^2 ). When you have the potential energy of the object, you put that in the equation of kinetic energy ( E = ½ * m * v^2), then v = sqrt{ (2 * E) / m } . That'll give you the answer.
Can someone help with this? A ball is dropped from a height (h) above the ground the speed of the ball just before it hits the ground is 7m/s. Calculate the height the ball is dropped from?
Acceleration due to gravity is 9.81 m/s/s no matter the mass or weight of the object. Given no air resistance, all objects accelerate downward at the same velocity. Feathers and sheets of paper have high drag coefficients (ie: wind resistance) so in an atmosphere like Earth's they fall more slowly. But a marble will fall with the same velocity and acceleration as a bowling ball or car or dump truck. Hope that clears things up. Added: When you get in to impact *forces* mass will enter the equations.
@rafaravioli I see that now. :) I don't get how he is dividing with a vector instead of the values of the vector, though. Maybe I missed something in my vector course or I'm being too mathematical.
So I wasted all this time watching this video not to have an answer on how fast the object is falling.....I need to know how fast it goes and if it keeps picking up speed the longer the object is falling.....such as if you dropped an object from 100 miles up or 500 miles up, etc. What is the maximum free fall speed of a big rock that weighs 50-100 lbs. ??? Hopefully someone can give me an answer....would appreciate it.....and if the object was falling for years, would it keep picking up speed or stable out at one constant speed??? I need to know the speed of things or living entities falling into the Bottomless Pit....this is Biblical stuff....I think if you dropped a big rock into the bottomless pit, it would still keep traveling down even after 20 years and still not hit the bottom, if there even is a bottom....Hence the name "BOTTOMLESS PIT"....Thanks.....Adios
Let's just assume ideal situation height being infinity (think of it as 10000 times the largest no. you can imagine , earth being very large or our bottomless pit), no air resistance and no other complicated stuff . Now if you throw the stone due to gravity it's speed keep on increasing until it reaches (approaches technically) to the ultimate speed 'c' ( speed of light in vaccum I.e. 299,772,458 m/s to be precise) and then no more acceleration . I am writing this statement based on the current (best) approved theory uptil now ( the special relativity by Albert Einstein) .
This is sometimes phrased as:
"It's not the fall that kills you - it's the sudden stop at the end."
lol brilliant
And that's on unaliving yourself 🗿🖐️
These video's are amazingly helpful. Just started biomechanics and some of these concepts are impossible to understand in written form. I dunno who this guy is but he's definitely got a talent for teaching this stuff.
i guess im asking the wrong place but does anybody know of a method to get back into an Instagram account?
I was stupid lost my password. I love any help you can give me.
@Zev Draven instablaster :)
@@elishadeshawn2599 comment bot
You can also use Energy formulas to calculate the final velocity.
E(potential) = E(kinethic) ⇔ mgh = mv² ÷ 2 ⇒ gh = v² ÷ 2 ⇔ 2gh = v² ⇒ √(2gh) = v
bro was so smart
OR you could just say:
V^2=2Gh
V^2=2(9.8)(Height)
thanks, i didn't want to watch the entire video. lol.
The point of the video is to solve the problem with knowledge everyone has
the entire point of Khan Academy is not to teach formulas, but to explain them, if you didn't catch that yet, then what are you doing here ?
the downward acceleration due to gravity is positive ..... the upward acceleration is negative bcz its decreasing and to downward its increasing .... so simple
Why is acceleration -9.8 ms^-2 ? Shouldn't it be in plus as it goes with the direction of gravitational force ? Please answer
In fact, it doesn't matter wether you say it's positive or negative, but it has to make sense according to the other variables. For example, if height is greater as it grows upwards, so is gravitity.
IIT nikel le kaa?
Depth is negative!
It depends on what you consider to be the positive direction. Is it upward or downward? You have to adjust the sign of your variables accordingly to that direction (because we're dealing with vector quantities). If it is upward, then: a = -9.8 m/s^2, otherwise it is: a = 9.8 m/s^2
I was so confused on brilliant momentum impulse theorem. This was so clear thanks!
@Ronc303c that's true :)
KHAN ACADEMY THE GOAT FR I SEE BIG BRO EVEN AFTER TWELVE YEARS YOU'RE STILL CLUTCHING UP FOR MY UNIT TEST TOMORROW
amazing how the video was 9 years ago and still such high quality and relevant
0:40 yes definitely don't jump from that height kids in all seriousness your video helped alot thanks
Only if the wind resistance is negligible and the initial velocity is 0. Also only on Earth.
@MrBaniboy
Because it happens on so many videos that someone says: it's much easier that other way or the way you showed is wrong/complicated. The videos are NOT meant to be the best/easiest/whatever solution to a problem. Videos Sal makes belong to a series. They almost all have. Every video expands the concepts of the previous. If you bothered to check this series contents, it's about Newton's laws of motion, motion and acceleration.
Reminding you that you commented here 10 years ago pal
if you plug in al the values you just mentioned you can see its the same thing he wrote.
but if you just think of it as the magnitude quantity of gravity and not as an acceleration vector you might forget to put the sign
If we take the direction of motion of the ball as the positive sense, then all variables will be positive, so as the acceleration due to gravity since the ball will accelerate faster and faster as it moves down before it hits the ground.
In this case it would make sense how we arrive at:
2*(9.8)*h = v^2
following the formula: 2as = v^2
I think if we take the direction of motion of the object as the positive sense, intuition will come much faster.
Great vid Sir Sal!
Sir Mahesh also explained this very well on Khan Academy India English!
I was wondering if you would be able to explain to me when calculating velocity regarding energy conservation we use v=(square root) (2gh) but when calculating velocity normally we can use v=delta distance / delta time.
Because by this video, those concepts (potential energy, kinetic energy) have not been dealt with in the list of videos on physics.
Which means when there is no air present, velocity of a piece if paper and the velocity of a 100kg stone wil b the same?
Nah air will not do that much but because of mass w=mg but I'm also confused that equations of motion don't include mass
What are you talking about? There's no reason why it shouldn't be said that downward acceleration is negative. It's just a convention. If you don't understand that, then you're "not so intellegent", and don't you EVER say that about Sal.
I like all your videos, good source of useful general knowledge.
Reminding you that you commented here 10 years ago pal
@@hashoo.group.ka.chairman thanks, but why?
You're amazing in teaching!
Reminding you that you commented here nine years ago pal
I'm so sorry, I already understood. I wasn't just not too awaked☺
Can you do this with variable g?
what application/program is this?
love this dudes sidebar comments
I video is awesome, I not even here because of class, it's cause I'm using this for kerbal space program lol.
I'm not understanding. Why did he(you) multiplied (2 a) Gomes displacement????
So you could just use the formula:
19.6h square root = Final velocity. :D
Reminding you that you commented here nine years ago pal
how to find the force exerted on an object by another object if it have an impact time
is it always the case that when you throw something up vi is positive and vf is 0, but when you throw something down vi is 0 and vf is negative?
Good stuff Khan. My only recommendation is...always use the sign convention only for accelerations and velocities. Never for distances. This way the formula will naturally tell you if the final velocity is negative or positive without imposing for instance a "negative squared root". Thanks.
Sal did calculate this using the displacement for the rock which is a vector quantity, not the distance of it which is a scale quantity.
V = sqrt(2*g*h) ... much easier :D
Why final velocity is in negative?
Your method is very weird. Why not simply use the equation to solve the potential energy of the rock first ( E = m * h * 9.81 m/s^2 ). When you have the potential energy of the object, you put that in the equation of kinetic energy ( E = ½ * m * v^2), then
v = sqrt{ (2 * E) / m } . That'll give you the answer.
i need more clarification
Wish the explanation didn’t have so much wasted time
2 people were hit by rocks
Can someone help with this?
A ball is dropped from a height (h) above the ground the speed of the ball just before it hits the ground is 7m/s. Calculate the height the ball is dropped from?
v^2=2gh
7^2=2*9.8*h
h=2.5m
Vf is : -11,0679
By the way, wouldn't the mass of the projectille influencie the velocity and the velocity time that it would take to "land"?
resume pls
or use h=1/2at^2
35.64 km/h
What if the object was heavy? Or light?
My guess it depends on the weight too but i see no weight in the formula
Can you explain please?
Acceleration due to gravity is 9.81 m/s/s no matter the mass or weight of the object. Given no air resistance, all objects accelerate downward at the same velocity. Feathers and sheets of paper have high drag coefficients (ie: wind resistance) so in an atmosphere like Earth's they fall more slowly. But a marble will fall with the same velocity and acceleration as a bowling ball or car or dump truck. Hope that clears things up.
Added: When you get in to impact *forces* mass will enter the equations.
@rafaravioli I see that now. :) I don't get how he is dividing with a vector instead of the values of the vector, though. Maybe I missed something in my vector course or I'm being too mathematical.
Reminding you that you commented here 10 years ago pal
Stop rock abuse...lol just kidding :) Great video as usual!!
The solution to the problem is wrong, the speed should be positive.
The solution is not wrong. The speed is indeed positive. But the velocity is not.
Because speed is a scale quantity and velocity is a vector quantity.
Yeah, but why it isn't just ah?
my y write yr proof t say that?please
So I wasted all this time watching this video not to have an answer on how fast the object is falling.....I need to know how fast it goes and if it keeps picking up speed the longer the object is falling.....such as if you dropped an object from 100 miles up or 500 miles up, etc. What is the maximum free fall speed of a big rock that weighs 50-100 lbs. ??? Hopefully someone can give me an answer....would appreciate it.....and if the object was falling for years, would it keep picking up speed or stable out at one constant speed??? I need to know the speed of things or living entities falling into the Bottomless Pit....this is Biblical stuff....I think if you dropped a big rock into the bottomless pit, it would still keep traveling down even after 20 years and still not hit the bottom, if there even is a bottom....Hence the name "BOTTOMLESS PIT"....Thanks.....Adios
Let's just assume ideal situation height being infinity (think of it as 10000 times the largest no. you can imagine , earth being very large or our bottomless pit), no air resistance and no other complicated stuff . Now if you throw the stone due to gravity it's speed keep on increasing until it reaches (approaches technically) to the ultimate speed 'c' ( speed of light in vaccum I.e. 299,772,458 m/s to be precise) and then no more acceleration . I am writing this statement based on the current (best) approved theory uptil now ( the special relativity by Albert Einstein) .
@MrBaniboy
You miss the point of this video series.
I got -10.002076. Could this be because I used more decimals?
A terrible overcomplication of the basic premise on how to calculate the velocity.
Khan Academy
m/s*
@superdau Would you mind clarifying and telling how, instead of posting a completely worthless comment? I haven't watched the whole series.
@DackIsBack I was just thinking about that.
Reminding you that you commented here 10 years ago pal
3:00
why is gravity going down negative? isn't it negative when upward?
It's not gravity, it's acceleration. I think.
There is no deceleration taking place, so I’d say it goes in the same motion as the velocity.
Bruh
Not recommended for large values of h... lol
Yeah, yeah, yeah, we get it, no air, you don't have to say it in EVERY SINGLE VIDEOS, you only need to say it one in the first video
redstone craft guy not everyone has seen them all!!
how can u say that downward accleration is negative ?
u are not so intellegent .........
Khan Academy