## Friday, February 11, 2011

### On A Roll

Kyle and Joseph did a "quick lab" (conceived, executed, analyzed, and presented during a single class period) this week on the rotational inertia of a roll of masking tape.

In their own words:
The Question - "What is the moment of inertia of a roll of masking tape? What is the coefficient of the moment of inertia for the tape as compared to a uniform annulus?"

The Design - "2 ramps of different and changeable angles, one with the masking tape rolling and one with a frictionless object.  Angles are changed so that the two objects have the same acceleration."

The race is shown here: pretty much the desired tie.  The video's a little dark because it was shot at 300 fps.

The Physics - "We used the net torque and net force equations to solve for the inertia.  We used the linear acceleration to find the angular acceleration.  The coefficient of the moment of inertia is the moment of inertia divided by the mass multiplied by the radius squared."

The Whiteboard:

The Takeaway - "Our moment of inertia calculation was a little bit off as compared to an annulus of the same dimensions, but not too far off. One of our assumptions was that the tape was of uniform density. Since the tape also had cardboard to keep its shape, our experimental moment of inertia was not completely accurate."