M-EngMom1: Conservation of Energy

PIRA: Unknown

Equipment: large pendulum bob suspended from the ceiling. It can be found in Room 4.

Procedure: "Before lecture the length of the pendulum should be adjusted so that when the demonstrator is backed head firmly against the wall and the pendulum bob is brought toward his face it will touch the tip of the nose.

"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).

"Also, it is wise to caution against pushing the pendulum from the face instead of merely releasing it." — Percy Carr (1970)

Note: The ceiling of Room 5 is about 7.0 meters (22.5 to 23 feet) from the floor and about 6.0 meters (19.5 to 20 feet) from the top of the fixed table in the room.