Rotational Inertia Lab
Purpose: Determine the factors that affect the rotational inertia.
There are three stations in this lab. One station will have a standard set up, one station will have extra length, the last
station with have extra mass. You will rank them from greatest to least moment of inertia.
You will calculate the moment of inertia two ways.
1st way:
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Measure the length of the entire main piece. (end to end)
Use this measurement plus the mass measurements written on the note cards at each station to calculate the
moment of inertia using the following eqns:
o For the rod itself: (1/12)mL2
o For each end piece: m(L/2)2
o Add all three values together to get the total moment of inertia.
2nd Way:
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There is a string attached to the PVC. You will attach a weight and put the string over the pulley (of negligible
rotational inertia).
You will hit the collect button. After pushing collect, drop the mass.
Analyze the velocity vs. time graph to get the acceleration of the mass.
Repeat dropping the mass three times and get an avg.
From the mass (hanging mass) and acceleration determine the tension in the string using Fnet=ma=mg-T.
Use the tension in the string and measurement of radius of the vertical PVC section to determine the torque
exerted on the rotating apparatus to accelerate it.
Convert the linear acceleration of the string as it moves around the PVC to angular acceleration using the radius
of the PVC.
Now determine the moment of inertia of the rotating apparatus, using τ=Iα
Analysis:
1. Find the percent difference between both rotational inertia calculations.
2. Rank the rotational inertia comparing your three different situations from greatest to least.
3. What factor has more effect on rotational inertia?
****Sample lab Data collection on the back****
Standard
Different Length
Different Mass
Mass main piece _____
Mass main piece _____
Mass main piece _____
Mass end 1 ______
Mass end 1 ______
Mass end 1 ______
Mass end 2 ______
Mass end 2 ______
Mass end 2 ______
Length from end to end _____
Length from end to end _____
Length from end to end _____
Diameter of PVC ____
Diameter of PVC ____
-pDiameter of PVC ____
Radius of PVC _____
Radius of PVC _____
Radius of PVC _____
Calculations:
Calculations:
Calculations:
Trial
Trial
Trial
a
a
1
1
1
2
2
2
3
3
3
Calculations:
Calculations:
a
Calculations: