Torque Bar

Equipment: A 1 meter long aluminum bar with a handle, a moveable hook and a 1kg weight. Optional: a spring scale and a ring stand.

What it does: The weight is hung on the movable hook at various distances from the handle. As the weight is moved along the bar, the work it takes to pivot the bar upwards about the handle changes noticably.

Concepts Demonstrated: Torque.

Classroom assembly:

1. Ask for a volunteer from the audience.
2. Ask the student to try to pivot the bar upwards about the handle with the weight hung at various distances from the handle.

1. Hang the spring scale from the ring stand.
2. Attach the handle of the bar to the spring scale.
3. Attach the mass to the hook on the bar and slide it back and forth to show the force registered by the scale. Note that the mass cannot be slid far along the bar before the scale registers the maximum reading of 100N.

• The weight of bar is approximately 5N
• The weight of bar and lower scale is approximately 9N
• The weight of bar, lower scale and 1 kg mass is approximately 19N

Cautions: None.

Setup Time: Short.

Difficulty: Straightforward.

Visibility: High. This demo is appropriate for large lecture halls.

Related demonstrations:

References: PIRA 1J40.10
Video Encyclopedia 04-10
Meiners 14-3.1; DHP Mo-5; DaR M-614

Original Construction: The bar was made from a 1 meter length of 1/2" diameter aluminum rod. The handle is a 6" length of 1.5" diameter aluminum tubing attached at right angles to the rod at one end.