Bouncing ball and angular velocity

1. Jan 21, 2010

sting10

Hello, im having a problem calculating the angular velocity of a bouncing ball.

At first this ball is thrown a distance and then hits the ground. Before it hits the ground it has no angular velocity. After it hits the ground it gets an angular velocity.

I have the inertia of the ball and coordinates of the ball travelling.

The whole proces I have on a video which was handed with the assignment.

3. The attempt at a solution

I have some teories of using the impulse between the ball and the floor but nothing seems to working quite well. Also I would have thought that the friction should have been given.

I would really appreciate if you guys could just give me some ideas.

Thx for the help.

2. Jan 21, 2010

tiny-tim

Hello sting10!
If the ball is rolling (ie not slipping), then the amount of friction makes no difference.

Use conservation of momentum, and for energy you'll need to find out what proportion of energy is lost on each bounce.

3. Jan 21, 2010

tiny-tim

Yes, of course.
Good. Now you'll need to study http://en.wikipedia.org/wiki/Coefficient_of_restitution" [Broken].

Last edited by a moderator: May 4, 2017
4. Jan 21, 2010

sting10

this was what I feared, all of my classmates are having problems with this assignment, oour teacher is away and no other physics teacher at my school can tell us how to do this. I am going to calculate this and post my results if im uncertain.

Last edited by a moderator: May 4, 2017
5. Jan 22, 2010

sting10

ok, does anybody have any other suggestions to solve this. I do not think I have the possibility of calculating the velocity of the ball when it hits the ground.

6. Jan 22, 2010

tiny-tim

To find the velocity of the ball when it hits the ground (given the initial velocity of the ball, and its initial height), use the standard constant acceleration equations.

7. Jan 22, 2010

sting10

the problem is that its not thrown from a 0 degree angle. I dont know the initial speed it is thrown with, almost nothing.

8. Jan 22, 2010

tiny-tim

let's see … you said …
… so what coordinates do you have, and what can you guess roughly from the video?

9. Jan 22, 2010

sting10

I have the x and y coordinates for when the ball is at its top height after each bounce also the coordinates at the point it is throw also the coordinates when it hits the ground. At the beginning of the video when the ball is thrown at an angle I guess is about -30 degrees. Also there is a timer in the video so I can see the time when the ball hits the ground.

10. Jan 22, 2010

tiny-tim

ok, so you have number of bounces (how many?), and you know both the horizontal distances and the times between bounces.

From that, you can find the horizontal component of speed between each bounce.

Similarly, from the heights, you can find the vertical components of speed after each bounce.

11. Jan 22, 2010

sting10

are you sure that would work when the initial velocity and the angle are unknown. wont that give two variables?

12. Jan 22, 2010

tiny-tim

I don't understand … surely nothing is unknown, you have all the x y and t coordinates you need?

13. Jan 22, 2010

sting10

ah, sry, stupid me, i can use the formulars for x and y and use substituion and find the initial velocity and angle and then use the formulars for vx and vy to find the velocity when it hits the ground, im gonna calculate.