Table of Mechanics Demonstration

List of Mechanics Equipment & Supplies

Lecture Demonstrations

Meter Stick Torque Beam, 1J40.20

Topic and Concept:

Location:

TorqueBeam01-400.jpg

Abstract:

A meter stick, suspended at the center, is used as a torque balance. Different combinations of weights hung at different distances can keep the beam balanced demonstrating how torque works.

Equipment

Location

ID Number

Torque Beam

ME, Bay C1, Shelf T

Weights and Weight Hangars

ME, Bay BA, Shelf #5

3/4" Rod and clamps

Rod and tackle cabinet near main lecture halls

Important Setup Notes:

Setup and Procedure:

  1. Place apparatus on lecture bench with numbered side facing audience.
  2. Behind the apparatus, mount a 3/4" rod to the bench with a table clamp.
  3. To this vertical rod, attach another rod horizontally so that it is about above the apparatus, low enough so that the central loop of the beam can slip onto the rod (this is how we will suspend the beam).
  4. From each of the outer loops, hang a weight hangar, and load up each with some amount of weight.
  5. Choose the relative positions on the beam of the weights so that the beam will balance.
  6. The moment of truth: unhook the chain from the stage left leg of the apparatus. Push the legs out to free the beam. If the previous two steps were completed appropriately, the beam will remain balanced. See photos below for some examples of weight - position combinations.

Cautions, Warnings, or Safety Concerns:

Discussion:

There are four torques acting on the beam: that due to gravity (weight of the beam), tension of the suspension string, and each of the two weights. If we set our origin at the 50 cm mark, the torque due to gravity and the tension go to zero. For the torques to balance giving us zero angular acceleration (keeping the beam balanced), we must have

r1·W1 = r2·W2 -> r1·m1 = r2·m2

where the r's denote the distance from the center of the beam of each weight hangar and the m's denote the total mass of the weight hangar.

TorqueBeam02-250.jpg

TorqueBeam03-250.jpg

TorqueBeam04-250.jpg

TorqueBeam05-250.jpg

TorqueBeam06-250.jpg

TorqueBeam07-250.jpg

TorqueBeam08-250.jpg

TorqueBeam09-250.jpg

TorqueBeam10-250.jpg

TorqueBeam13-250.jpg

TorqueBeam14-250.jpg

TorqueBeam15-250.jpg

Videos:

References:

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