The traditional introductory-level meterstick-balancing lab assumes that students already know what torque is and that they readily identify it as a physical quantity of interest. We propose a modified version of this activity in which students qualitatively and quantitatively measure the amount of force required to keep the meterstick level. The setup for this experiment also introduces upward forces in addition to downward forces. In this very accurate experiment, the torque equation can be discerned directly from the data, and torque's symmetry between upward and downward forces naturally arises.
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Here and throughout the experiment, the meterstick's levelness can be checked with a level or against a grid backdrop (graphing paper, brick wall, etc.), or by measuring the height of different points on the meterstick from the table.
7.
Rubber stopper attachments come as accessories with many force sensors, such as http://www.pasco.com/prodCatalog/PS/PS-2104_pasport-force-sensor.
8.
Friendly reminder: Re-tare the force sensor after inverting it!
9.
There is a gap in the data due to the width of the force sensor and hanging weight. Also, one cannot move the force sensor too close to the fulcrum point without the torque of the hanging weight about the force sensor becoming greater than the torque of the meterstick's weight about the force sensor, causing the meterstick to rotate out of the stand; this problem presents an opportunity to discuss statics problems with students.
10.
Assuming the length of the string (the hypotenuse) is kept constant.
11.
Or rather, the supplement of the angle, which results in the same sine.
© 2014 American Association of Physics Teachers.
2014
American Association of Physics Teachers
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