Lab: Acceleration of a cylinder

My original goal with Quantus was to collect data accurate enough to discriminate between the acceleration of different objects (cylinder, sphere, torus, etc.) when rolling down a ramp, which is a function of a rigid body's moment of inertia.

In many high-school physics curricula, moment of inertia is not taught and in labs rolling objects are treated like point masses (e.g. boxes sliding down frictionless inclines). Regardless, the data collected usually have such large experimental errors that it is not possible to recognize the decrease in acceleration due to the rolling body's moment of inertia. This reduced acceleration can be solved analytically for most rigid bodies.

I conducted an informal lab just for fun (you know you're a geek when...) to see if Quantus is able to produce data accurate enough to determine the true acceleration of a cylinder rolling down a hill. Theoretically, this acceleration should be two-thirds the acceleration of a point mass. 

To perform this lab, I rolled an unopened cylindrical 1kg peanut butter jar (very scientific) down an incline measured to be 5.87°. The acceleration determined from Quantus' data was 0.6202 m/s². If we were to treat the cylinder as a point mass the theoretical acceleration would be 1.002 m/s² (38.1% error). However, when considering the cylinder's moment of inertia the theoretical acceleration is 0.6682 m/s² (only a 7.1% error). Quantus produced data accurate enough to identify the true acceleration of a cylinder when rolling down an incline. The original data as well as an informal lab write-up are below.


Experimental Procedure

Quantus is really easy to use.

  1. Plug in the SD card and turn on Quantus.
  2. Push the black button to start collecting data.
  3. Roll the cylinder down the ramp.
  4. Push the black button again to stop collecting data.