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Physics Department

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Physics 121 week 10


Torque Wrench

After clamping the metal to a table, you can show students how a torque wrench works as you attempt to tighten or loosen the bolt.

Walking the Spool

The spool will either “wind-up” or “unwind” depending on what angle you exert a torque by pulling on the string. You can also challenge your students to determine at what critical angle can you pull the string such that the spool just slides across the table?

Torque Feeler

This "T" shaped bar has an adjustable location to attach masses. Have students rotate the bar up while their arms are extended outwards. Then, move the same mass to a different position to allow students to feel the difference.

Moment of Inertia

Inertia Wands

Two identical wands have the same mass, but in one wand the mass is located at its center, and on the other the mass is located on the ends. Holding the wands at their centers, have students attempt to rotate the wands to feel how mass distribution affects an object’s moment of inertia.

Moment of Inertia Races

Using an inclined plane compare how an object’s moment of inertia influences its motion down the ramp. Discs, balls, and cans are provided to offer plenty of different objects. You could have the students predict the outcome of the race before releasing the object.

Rotational Energy

Rolling Spool

A large spool is rolled down a meter stick along its small axis, and allowed to roll onto a table. Even though angular velocity is constant, since tangential velocity is larger on the large axis the spool will speed up when it contacts the table.

Ball Transfers to Cup (Faster than "g" acceleration)

Use the wooden dowel to hold the hinged plank open. Place the ball in the depression at the top of the angled plank. Then, quickly remove the dowel by pulling it outwards from the bottom. The plank rotates faster than the ball falls, so the ball will fall straight down landing in the cup.

Angular Momentum

Angular Momentum with a Rotating Stool

A rotating stool or platform is used to have student volunteers show what happens in various situations...

  • CHANGING MASS DISTRIBUTION: Students hold weights in outstretched arms and are given a slight push, once spinning, ask students to bring their arms into their chest.
  • ELIMINATING EXTERNAL TORQUEStudent is given a baseball bat and asked to swing it while feet are not touching the ground. Compare what happens with when their feet are touching ground and they swing the bat.
  • BIKE WHEEL EXERTS INTERNAL TORQUE: Student is asked to hold a bike wheel from its pegs while sitting on the stool. Spin the wheel and then have the students move the wheel's axis.

Gyroscopic Precession

Rotate a bike wheel and then suspend it by the string. The wheel will remain relatively vertical but begin to precess due to the conservation of angular momentum.

Rotational Equilibrium


Balance a meter stick on a fulcrum at its center. You can use the adjustable hangers to change where masses are hung so that the meter stick balances. This is a great demonstration to allow your students to calculate a theoretical statics problem, and then verify their prediction!

Torque on a Lever Arm

Just like above, but the fulcrum is at the end of the meter stick. This demonstration quickly provides a qualitative result for a statics problem.

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