Physics B
Torque Lab
Purpose: To use torque to find the mass of an unknown.
Theory: Static equilibrium requires that the sum of the torques on a system is zero. It also requires that the
sum of the forces is zero. In equation form
 = 0
F = 0
In this lab, you’ll use torque to determine the mass of an unknown. An individual torque can be calculated
using the equation  = r F sin .
Equipment:
1 meter stick
1 meter stick support and support clip
3 hanger clips
2 mass hangers and set of masses
unknown mass
Prelab Setup:
1. Measure and record the mass of your meter stick and all clips, and record these masses in a table
of data.
2. Find the center of mass of your meter stick. Do this by balancing it on the support with the support
clip. It should be near the middle, but probably will not be exactly in the middle. Record the meter
stick center of mass.
3. Move the meter stick support clip 10 - 20 cm away from the center of mass of the meter stick.
4. You are now ready to ask for an unknown mass.
Procedure: Devise a method to find the mass of your unknown using torque. You must leave the meter stick
support clip 10 – 20 cm away from the meter stick center of mass to do this. At your disposal are your
hanger clips, your mass hangers and your set of masses.
After you have found the mass of your unknown, alert your instructor. He or she will check the mass of
your unknown on a triple beam balance.
Data: Must include all masses and meter stick positions, clearly labeled.
Drawings: Must include a labeled sketch of your setup. Also must include a diagram showing all forces and
moment arms, clearly labeled.
Discussion: How close did you get to the actual mass using this method? What was your percent error?
What did you have to include in your torque calculations? How does what you did relate to the operation of
the triple beam balance you use in lab?
3/7/2016
Bertrand and Moreno