PURPOSE: To show that all objects fall at the same rate referred to as Galileo's Law of Falling Bodies.
DESCRIPTION: Drop a feather and a penny at the same time to show that the feather falls slower than the penny in the presence of air friction.
Then use long vacuum tube to do the same thing. The vacuum tube contains a penny and feather.
The tube is evacuated by turning on a vacuum pump for a few minutes so that the atmospheric air pressure inside is removed. The feather is painted with fluorescent paint so that it will glow under a black light and be visible to the class. Turn off the room lights and hold the tube close to the black light. Turn the tube end-over-end so that the paper and washer are made to fall from top to bottom simultaneously inside the tube. The paper is visible from the UV light as it falls inside the tube. Ask the class to listen for the sound of the washer striking the bottom of the tube.
EQUIPMENT: Vacuum pump, sealed tube with washer and paper.
SETUP NOTES: The vacuum tube and vacuum tube are stored in room 055.
Tube can be evacuated before class and the demo can be done in reverse thus saving the class time required to evacuate the tube.
The tube is made by facing the inside surface and constructing tight fitting end caps with double o-ring seals. One end cap has a vacuum valve connector.
Updated by Jun Qi in 3/1/2000