# Homework Help: How come a bouncing ball does not exhibit SHM characteristics?

1. Jul 15, 2008

### .NoStyle

1. The problem statement, all variables and given/known data
How come a bouncing ball does not exhibit SHM characteristics?

2. Relevant equations
no clue

3. The attempt at a solution

When I think of SHM, I don't think of contact forces. In the bouncing call case, there is a contact force present when the ball hits the ground.

Would the graph for a bouncing ball look curved as it approached it's height, but then a sharp V as it hits the ground?

Thanks

2. Jul 15, 2008

### Defennder

What is the defining characteristic of a system in SHM? Does this apply to a bouncing ball?

3. Jul 16, 2008

### NBAJam100

Think of it this way...

As the ball bounces, why do the time intervals that the ball is in the air get smaller the longer the ball bounces... it is missing a certain force that is essential to SHM...

4. Jul 16, 2008

### Defennder

The fact that the ball is airborne for shorter periods of times after each consecutive bounce is not the reason why it doesn't count as SHM. One can envisage a hypothetical scenario where the collision of the ball with the floor is entirely elastic; no kinetic energy is lost to the floor as heat, sound etc. There is something more fundamental in the definition of SHM than that consideration.

5. Jul 17, 2008

### NBAJam100

maybe were on a different wavelength here, but i was hinting at... its not SHM because it has no restoring force... aka... why the ball doesnt return to its original position. I wasnt saying thats why it isnt SHM, i was using that as an example as to aid him in finding the answer.

6. Jul 17, 2008

### LowlyPion

From Wikipedia:
"In words, simple harmonic motion is "motion where the force acting on a body and thereby acceleration of the body is proportional to, and opposite in direction to the displacement from its equilibrium position" (i.e. F = − kx)."

Your instinct looks correct. The contact with the floor is an impulse force that perturbs the constant accelerated motion that it is otherwise subjected to in one direction of gravity only.)