Rolling motion of a cylinder down an incline

[mlostrac]

Homework Statement

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

Homework Equations

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?

 

[srmeier]

Did you put your angle in radiants?

 

[tvavanasd]

Assuming smooth rolling with no resistance...

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?

 

[mlostrac]

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?

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

 

[mlostrac]

Did you put your angle in radiants?

yes i did, 25.6 degrees = .46 rad

 

[tvavanasd]

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

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.