# Superball physics problem

1. Dec 26, 2003

### AKemp

Hi everyone,

Any help on this problem would be appreciated. Say you have a super ball, point mass. How could you throw it so it bounces in a parabolic path between two points indefinitely? I had no idea where to start on this one.

Thanks.

Last edited: Dec 26, 2003
2. Dec 26, 2003

### HallsofIvy

How could you get anything to bounce between two points in a parabolic arch even twice?

If these are points on a plane, then in order that the ball bounce from one point to another, it must start from one point at a specific angle. It then lands at the other point (neglecting air resistance) at the same angle and will continue in the same direction, bouncing at the same angle. In order to get the ball to bounce back to the starting point, you will have to have some sort of barrier there. If you have a vertical wall at both points, then you need only calculate an initial velocity (there will be more than one solution) so that the ball will move from the first point to the second. The rest of the motion will automatically follow from the "elastic collision" (and the ball can be treated as a point mass so you don't need I).

3. Dec 26, 2003

### Hurkyl

Staff Emeritus
I know from experience that the rotational motion of a super bounce ball strongly affects its dynamics. The two most amusing examples are when you spin one as you drop it to the ground it will bounce left, then right, then left, then right, etc. The other is if you throw it down and forward at, say, 45 degree angle and it bounces up to hit the bottom of a barrier (say, the underside of a table), it will come back to you!

I have no idea how to model this behavior, though...

4. Dec 26, 2003

### HallsofIvy

Ah! You are going to use "backspin" on the ball to make it bounce back? Then that will depend upon the friction between the ball and surface won't it?

5. Dec 27, 2003

### pallidin

An aspect of the superball(depending on manufacturer) is it's extremely high contact surface friction. This attribute provides for many of the seemingly bizzare behaviors of a superball.
With the original Whammo superball, one can roll the ball along a flat surface with little ease.
However, if one pressed on the ball and attempted forward movement, the balls' motion is impeded due to very high contact surface friction.
Throwing a similar superball at a surface is roughly the same as pressing and rolling it. Resitance. This resitance is reflected.

6. Dec 29, 2003

### TillEulenspiegel

How could you throw it so it bounces in a parabolic path between two points indefinitely?
You couldn't.
Unless it's a magic super ball or your either a wizard with special powers or a scientist who's figured out a way to violate the laws of Thermodynamics.