Understanding Newton's Third Law: The Impact of Forces on Objects in Motion

[malu]

Why would you think the velocity of the smaller object goes to zero?

Because i know that when smaller block pushed on bigger block, bigger block wants to stay in its inertial position so the bigger block pushes back...Ya this is my question with what force does the bigger block pushes back ?

if it is 20 N back then is that dependent on the mass of bigger block or not ?

Treating this as a simple inelastic collision, there is no mass that will make the velocity equal to zero.

i mean to say how much bigger block at-restor how much mass at-rest (to which this block collides) is required to make velocity zero ?

 

[Doc Al]

i mean to say how much bigger block at-restor how much mass at-rest (to which this block collides) is required to make velocity zero ?

Again I ask: Why do you think the velocity goes to zero?

 

[malu]

Again I ask: Why do you think the velocity goes to zero?

i am not sure whether velocity goes to zero or not that's what i am asking ?
but my real question is

Because i know that when smaller block pushed on bigger block, bigger block wants to stay in its inertial position so the bigger block pushes back...Ya this is my question with what force does the bigger block pushes back ?

if it is 20 N back then is that dependent on the mass of bigger block or not ?

 

[Doc Al]

Because i know that when smaller block pushed on bigger block, bigger block wants to stay in its inertial position so the bigger block pushes back...Ya this is my question with what force does the bigger block pushes back ?

The details of the momentary force that the blocks exert on each other during the collision are complicated to estimate.

Forget the complication of the applied force of 20 N. Imagine that your first block is moving at some speed, say 1 m/s, when it hits the other block. Neither block 'wants' to change its motion, thus they exert forces on each other. That force may be quite high, but the resulting impulse can be calculated by comparing initial and final velocities of the blocks. (Those velocities can be calculated using conservation of momentum.)

 

[malu]

Actually i was really looking for the scenario of impact so i came through mit lectures http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/embed07
in one of the experiments, he is showing the impact load along the time scale i am really trying to understand that, i hope this may help out.

 

[Doc Al]

Actually i was really looking for the scenario of impact so i came through mit lectures http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/embed07
in one of the experiments, he is showing the impact load along the time scale i am really trying to understand that, i hope this may help out.

Where exactly is the point in the lecture where he discusses impact forces?

 

[malu]

Where exactly is the point in the lecture where he discusses impact forces?

at 35.49, the experiment starts and then then after the experiment he shows the impact on time scale have a look its amazing

 

[Doc Al]

at 35.49, the experiment starts and then then after the experiment he shows the impact on time scale have a look its amazing

Yes, nice demo. What he's demonstrating there is that the apparent weight goes to zero for an object in free fall. And as it collides, the apparent weight shoots up to a momentarily high value. Good stuff. The exact value of the force depends on the cushioning that he's dropping it on. Note that he drops it on a cushion--if he didn't, the thing would break because the impact forces would be too high.

(You can do a sloppy version of this on your own by jumping on your bathroom scale. Don't jump too hard or you'll break it.)