Concept Overview
Conservation of Energy
Lecturer Procedure for Demonstration
Steps to Follow
- With the bowling ball in your hands, back up so that your back is to the chalkboard.
- Raise ball so that it is touching your nose.
- Keeping your back pressed to the chalk board, release the ball.
Expected Result
The ball will swing away from you. When it returns to you, it will not hit your face.
Caution:
- After releasing the ball, do not lean forward or you will be putting your face in the direct path of the bowling ball.
- Do not give the ball a push when you release it. If you do, the extra energy you have imparted into the system will cause the ball to hit you in the face on its return.
Historical References; Taken from original work of Percy H. Carr, 1970
“After telling the students that if one really believes the conservation of energy principle he should be willing to assume this position as shown and then let the pendulum swing freely away, firm in the conviction that on its return the bob will not bash in his face. Then demonstrate."
“After the demonstration it is wise to tell the students that backing against the wall is not so much to make the demonstration dramatic as it is to set the conditions such that a broken nose will not result. If one is not against a firm station such as furnished by the wall, he is likely to lean slightly forward as his eyes follow the receding pendulum with the result that the nose meets the pendulum upon its return.
“If this caution is not made, some curious student after class may try the experiment while standing in the open and receive a bloody nose as a consequence. (I saw this happen at Cornell once)"
Video Demonstration
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