# About controlling collision conditions experimentally

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1. Jul 17, 2015

### Phylover

1) Are there any ways to control the impulse in an collision in a lab condition? I.e. if I set an object connected to a spring and try to hit a ball using the object, are there any ways to control the impulse of the collision?
2) How to detect the change from slipping to pure rolling experimentally, apart from using the v-t graph in obtaining where the acceleration drops abruptly?

2. Jul 17, 2015

### Staff: Mentor

1) to control the impulse, control the speed.

2) to detect slip vs roll, use a high speed video camera. A cell phone camera may be enough. Make the image include the clock in the image. Put visual dots on the ball to make rotation easy to see.

3. Jul 17, 2015

### tonywp955

For 1), I don't quite understand. Do you mean controlling the speed of the object when it collides with the ball? How does it work (to control the impulse)? Could you explain more please? (But the collision time may be different and although the speed before the collision is the same, the final speed may not be controlled?)

4. Jul 18, 2015

### Staff: Mentor

Perhaps you could explain what you mean by controlling the impulse.

5. Jul 20, 2015

### tonywp955

I mean that I need to control the momentum change of the ball initially at rest ( the ball that I hit using an object connected to a spring)

6. Jul 20, 2015

### Staff: Mentor

Clearly, the more momentum in the object, the greater the momentum of the ball. Perhaps it is the precision of the ball's momentum is the issue. I don't don't have enough information from your question to know.

With all due respect, if you want expert help with the design of your experiment, you must do more than post a two sentence question to an online forum.

7. Jul 20, 2015

### Phylover

For the experiment I am investigating on the effect of the position of hitting the billiard ball on the time it takes for the ball to obtain pure rolling.

The detailed theory can be found here: http://www.real-world-physics-problems.com/physics-of-billiards.html
Basically if I hit the sweetspot of the billiard ball, it will just roll without slipping; hitting any point above or below the sweetspot causes the ball to slip, until the friction acts on it for a long enough time to bring it back into pure rolling.

Hence, as a controlled variable I think I need to control the momentum change of the ball. (if different momentum of the ball, it will take different time to obtain pure rolling) How can I actually do it?

For now, I design an experiment which fixes the compression of the spring, so that the pointy thing attached on the spring hits the billiard with a controlled constant speed. However, in this case there is no guarantee that I can control the impulse acting on the ball. Are there any way I can do it? (by its collision with the pointy thing)

8. Jul 20, 2015

### Staff: Mentor

For the moving object, you could use balls of several diameters. The relative diameters of the two balls would determine the point of impact.

They could roll down a ramp or swing like a pendulum on a string.

A video record with a frame by frame review should give a very accurate measure of the pre and post impact velocities. If the velocities vary a little, use a statistical analysis of the results.

Good luck