Download Moment of Inertia for Bicycle Wheel

Moment of Inertia – Spinning Bicycle Wheel Activity
Prior to students starting the activity you may want to remind them of
previous material covered. The first thing students will need to remember is that
they need to look at both object as independent systems.
For the falling weight:
T
F = ma
So: T-mg = ma
mg
For the turning wheel:
=I
and
a= r
So: Tr = I  = I * a/r

a
T
Substituting in T from the falling weight in the equation for the turning wheel, we
get:
(mg+ma)*r2/a = I*a/r
Solving for I: I = mr2(g+a)/a
In order for the calculation to work out, a is negative if the weight descends.
Once the students are given the some or all of the material above, the can work on
solving the video analysis for the moment of inertia.
Sample of verbal instructions for students:
For the activity that we have planned today, you and a partner will work together to
find the moment of inertia for a wheel that is being accelerated by a falling weight.
Some things that you will need to keep in mind while completing this task is that
you will have to look at the motion of the falling weight and the motion of the
spinning wheel separately. Once you have equations for both, you can substitute
one equation into the other for 1 equation with 1 unknown. Make sure to write
down all the data that you took from the video (frame numbers, measurements,
etc.). You will have 1 hour to complete the activity.
For some of the after activity questions, you could pose:
What would happen to the moment of inertia if the radius was half as big?
What would happen to the moment of inertia if the mass were twice as heavy?
What would the moment of inertia be if the wheel was pulling the weight up?