Where is the center of mass?: Testing Experiment

Aim

Find the center of mass of a ruler.

Prior Knowledge

1. Static friction
2. Center of mass
3. Torque

Description of the Experiment

1. Watch the first experiment. Explain why Mike's fingers met in the middle of the ruler.
2. In the second experiment the ruler will be slid off the edge of the table. Predict at what point it will tip. What physics principles did you use to make the prediction? Do not watch the movie before you make the prediction.
3. Watch the movie. Did your prediction match the outcome of the experiment? Why do you think it did not? How do you need to modify the reasoning that you used to make the prediction?

Youtube movies can be stepped frame by frame using the , and . keys on your keyboard. If you want to download the movie to your computer, right-click or control-click HERE.

Youtube movies can be stepped frame by frame using the , and . keys on your keyboard. If you want to download the movie to your computer, right-click or control-click HERE.

Questions

1. Provide several explanations of why the ruler did not slide at the 50 cm mark when Mike was pushing it with his finger?
2. Design an experiment to test each explanation. Before you perform each testing experiment, make a prediction of its outcome based on the explanation under test.
3. Go to mechanics puzzles,to "finding the mass of a meter ruler" experiment. Watch the fist experiment there and explain why in this experiment the ruler slid at almost the 50 cm mark.