Torque Lab

Calculate the mass of an object.

You should have the following materials at your lab table.

1. one PVC pipe

2. one wood dowel

3. one metal rod

4. a roll of masking tape

5. two metersticks

Draw a sketch of your set up and record:

• mass
• length
• center of mass

of each object on your sketch.

1. Measure and record the mass of the PVC pipe.

2. Locate and record the center of mass of the PVC pipe.

RECALL

• The center of mass is the balancing point of the pipe/dowel/rod.
• The center of mass of an object can be treated as the position where the force of gravity acts on the object. Consider all the mass of the object to be located at the center of mass.

3. Locate and record the center of mass of the wood dowel.

4. Insert the wood dowel into the PVC pipe. Insert no more than 25% of the wood dowel into the PVC pipe.

5. Secure the wood dowel with a SMALL piece of masking tape. Use just enough tape to prevent the dowel from sliding in the pipe.

6. Locate and record the center of mass of the combined pipe-dowel.

HINT - Try balancing the pipe-dowel on the edge of a meterstick.

QUESTION - Which would more accurately locate the center of mass?

• a wide balancing edge
• a narrow balancing edge

7. Knowing the center of mass of the:

• PVC pipe
• wood dowel and
• combined pipe-dowel

sum the torques and calculate the mass of the wood dowel.

QUESTION - Which center of mass position should be defined as the origin?

• center of mass of the PVC pipe
• center of mass of the wood dowel
• center of mass of the pipe-dowel

Your choice of origin should result in one clockwise torque and one counterclockwise torque.

Add to your sketch:

• an arrow where the force of gravity (weight) acts
• an arrow that points from the origin to the point where the force of gravity (weight) acts.
• note the angle between the above arrows.

8. Bring your completed team score sheet and wood dowel to your teacher. Your teacher will mass your wood dowel. If your mass is off by more than a couple of grams, reevaluate your data collection and analysis.

DON'T FORGET A SKETCH.

9. Locate and record the center of mass of the metal rod.

10 Insert the wood dowel and metal rod into opposite ends of the PVC pipe.

11. Secure the dowel and rod with a SMALL piece of masking tape. Use just enough tape to prevent the dowel and rod from sliding in the pipe.

12. Locate and record the center of mass of the combined rod-pipe-dowel.

13. Knowing the center of mass of the:

• PVC pipe
• wood dowel
• metal rod and
• combined rod-pipe-dowel

sum the torques and calculate the mass of the metal rod.

QUESTION - Which center of mass position should be defined as the origin? Your choice of origin should result in two clockwise torques and one counterclockwise torque or one clockwise torque and two counterclockwise torques depending on which side of the table you're sitting.

14. Bring your completed team score sheet and metal rod to your teacher. Your teacher will mass your metal rod.

15. Your grade will be determine by the accuracy of your mass calculation. ONE point off for each percent error.