# Homework Help: Rolling motion of a cylinder down an incline

1. May 22, 2010

### mlostrac

1. The problem statement, all variables and given/known data
Assuming smooth rolling with no resistance, it can be shown that the acceleration of a solid cylinder down an incline is equal to:

a = 2/3 g sin(theta)

The goal of my lab is to test the validity of the above equation

2. Relevant equations

3. The attempt at a solution
The acceleration values I found using my measured inclination angles, are smaller than what they would be if i plugged them into the above equation. What does this mean? If this is the case, does that mean that the above equation isn't valid?

2. May 22, 2010

### srmeier

3. May 22, 2010

### tvavanasd

Were you able to eliminate all rolling resistance in your lab? With rolling resistance present would you expect acceleration to be higher or lower than theoretical? How close to theoretical were your measured accelerations?

4. May 22, 2010

### mlostrac

I'm not sure, but I'm going to assume that I didn't eliminate all resistance; I rolled a hockey puck on it's side down a wooden board.

I'd assume that if resistance was present that it would cause the acceleration to be lower than theoretical.

One example comparing theoretical and measure for a 5.7 degree incline:
theoretical = 0.649 m/s^2
measured = 0.073 m/s^2

5. May 22, 2010

### mlostrac

yes i did, 25.6 degrees = .46 rad

6. May 23, 2010

### tvavanasd

Your assumption is correct, but the discrepency seems quite large.
How did you arrive at your measured accel?
Were you able to sample multiple points during the test or simply average over time and displacement?
How long was the ramp?
Did you find the theoretical vs measured to be closer as the ramp slope increased?

Shouldn't be significant, but 25.6 degrees is 0.447 radians.