TORQUE / FINDING THE CENTER OF MASS
This lab is designed mainly for mathematics as a way of showing how math can be used in the area of
Physics, and how the processes involved are often used in the real world.
MATERIALS NEEDED: (per station)
1. Meter stick
2. Four stick hangers
3. Three hangers to hold slotted weights
4, One ring
5. Four one-hundred gram slotted weights, plus a few assorted extras
6. Table clamp
Note: Pre-weighed beanbags could be used in place of formal weights.
1. Have everyone set up table clamp, and put center stick hanger on meter stick.
2. Weigh each set (stick hanger with slotted weight hanger) of hangers separately, record weights and put
one set on each end of the meter stick.
3. Balance the meter stick with hangers equal distance from fulcrum (fulcrum = center of mass)
4. Explain formula ( F x length of arm = F x length of arm ) on board or overhead, showing some
5. Have students place 100 grams (plus weight of hangers) at 40 cm from fulcrum on one arm of the lever.
6. Have students figure out mathematically how far they should place 200 grams (plus weight of hangers)
from the fulcrum in the opposite direction.
7. Have students verify their answer using their balance beam. Have them note any differences and
8. Give out new data …100 grams ( plus hangers ) at 20 cm from fulcrum
200 grams ( plus hangers ) at ??? cm from fulcrum
By both math and experimentation the students must figure out the missing
9. Give more new data … as pictured:
Discuss: How should one mathematically figure out how far from the fulcrum force 'C' should be?
Have students work on this on their own. Then explain.
10. Let students experiment on own.
11. Explain how torque problems such as these are used in the real world, and give some application
problems for classwork or homework.
Example: A large crane, pictured to right, has a force
arm 70 feet long. It has a counter weight of 4000 lbs.
how far down the resistance arm must the counter weight
be in order to balance a 3000 lb. Load?