MINIMUM SPEED FOR

CIRCULAR MOTION IN A VERTICAL PLANE

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PURPOSE:

The intent of this activity is to measure the minimum tangential speed of a marble moving in a vertical circle.

APPARATUS:

Hidden from view in this picture is a metal rod supporting the 78 rpm record, which was tapped to receive the mounting screw for the pulley.

PROCEDURE:

1. Set up the apparatus as shown in the picture above. Be very careful to make sure that the laser and photocell are aligned.
2. Place a marble in the cup and add nuts to the counterweight screw to balance the apparatus.
3. Configure the Science Workshop interface to monitor digital input 1, smart pulley (rotational).
4. Choose a graphical display of angular velocity vs. time.
5. Use the calculator function of Science Workshop to input a formula for tangential speed (angular velocity * value of circular motion radius).
6. Add a graphical display of tangential speed vs. time.
7. Start the record rotating, and record data.

DATA:

(Using the Pasco Science Workshop 500 Interface)

The unloading of the marble causes the rotating record to be unbalanced, resulting in a net torque that is alternately clockwise and counterclockwise, causing acceleration for half of a rotation, and deceleration for the other half of the cycle. The point at which unloading is obvious on the graph and the speed at which the marble fell can be compared to the theoretical value.