Penny and Feather Drop
Brief Description
This demonstration visually compares the effect air resistance has on free falling objects. When analyzing the motion of a free falling object, every force acting on it must be considered. There is a gravitational force pulling it down, and a force due to air resistance pushing it up. This force due to air resistance is greater for lighter objects, as they have less resistance to changes in motion. But if we drop two objects of differing mass at the same time and remove the air, they experience the same acceleration due to gravity and fall at the same time.
Materials
Vacuum tube with penny and feather, vacuum pump, and hose.
Setup
Place the vacuum tube and pump on the table. Connect the hose to the vacuum pump, and make sure there is enough oil in the vacuum pump by checking the level from the window on the side.
Performing the Demo
First show the students that the penny does reach the bottom of the tube before the feather does. Then hook up the vacuum pump via hose to the tube and turn it on. After a minute, close the valve and take the hose off of the tube. Then show the students that the penny and the feather reach the bottom of the tube at the same time.
Safety and Other Notes
Do not place anything over the valve when releasing the vacuum. Do not swing the tube around.