Bouncing ball and angular velocity

[sting10]

Hello, I am 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.

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.

 

[tiny-tim]

Hello sting10!

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.

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.

 

[tiny-tim]

(Please always reply on the thread, not by private message )

Does this mean I have to find the velocity the ball hits the ground with.

Yes, of course.

And I have now calculated that 20 % of the height goes lost after each bounce

Good. Now you'll need to study http://en.wikipedia.org/wiki/Coefficient_of_restitution" .

 

[sting10]

(Please always reply on the thread, not by private message )


Yes, of course.


Good. Now you'll need to study http://en.wikipedia.org/wiki/Coefficient_of_restitution" .

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 I am uncertain.

 

[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.

 

[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.

 

[sting10]

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

 

[tiny-tim]

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

let's see … you said …

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.

… so what coordinates do you have, and what can you guess roughly from the video?

 

[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.

 

[tiny-tim]

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.

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.

 

[sting10]

are you sure that would work when the initial velocity and the angle are unknown. won't that give two variables?

 

[tiny-tim]

are you sure that would work when the initial velocity and the angle are unknown. won't that give two variables?

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

 

[sting10]

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