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Physics Lab: Fulcrum Measurements

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1. Suspend the meter stick by a string from its center.

2. Notice carefully where it balances. It probably will not balance exactly at 50 cm. All distances must be measured to this point (called the fulcrum).

3. Hang a 200 g mass on one side and a 50 g mass on the other and adjust the distances from the fulcrum until the meter stick balances.(Be sure to account for the mass of the hanger from which you are suspending the masses. This can either be part of the total mass or, alternatively, if you are using something like coffee cups to hold the masses, their masses need to be matched perfectly before starting the experiment. You can do this by first checking to see how close they come to each other in mass and then simply add small weights, like thumb tacks or small paperclips to one cup to make the two cups have equal starting masses. Leave these "mass equalizers" in the coffee cup and now you have a matched set of mass holders to use for the lever. Now add the additional 200 g or 50 g to the cups as called for by the experiment. Disregard the actual mass of the coffee cups since they are matched.)

Measure the distances from the 200 g and 50 g masses to the fulcrum.
200 g: cm
50 g: cm
Repeat using a 100 g mass and 300 g mass.
300 g: cm
100 g: cm
Formulate a general statement concerning the relationship of mass and distance.
Repeat using two 100 g masses.
100 g: cm
100 g: cm

Does your general statement still hold?

4. Hang a 50 g and 100 g mass on one side of the fulcrum at two different locations and balance a 200 g mass on the other side.
Measure the distances to the fulcrum.
50 g: cm
100 g: cm
200 g: cm
Does your general statement still hold?

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Solution Preview

Let a force F be applied to an object at a displacement r from a certain point (fulcrum).
We define the torque vector t as the cross product:
Since two vectors define a plane, the torque is a vector perpendicular to the plane defined by r and F.
The toque vector represents the tendency of the force to rotate the object about the fulcrum, and the rotation plane ...

Solution Summary

The expert examines fulcrum measurements for physics labs.