Dropping Coin and Feather in a Vacuum

This demonstration shows that in the absence of air resistance, all objects fall at the same rate. A coin and a feather dropped in a tube filled with air fall at different speeds, but when the tube is evacuated, they fall together.

1. Begin with a transparent rigid plastic tube filled with air. Hold it vertically and let the coin and feather fall. Point out that the feather drifts down much more slowly.
2. Attach the vacuum pump to the tube and evacuate the air until the pressure is very low. Close the valve and disconnect the pump.
3. Hold the tube horizontally and gently shake so the coin and feather rest side by side on the inner wall.
4. Quickly rotate the tube to vertical and observe both objects falling at the same rate.
5. Optionally, allow some air back into the tube and repeat to show how increasing air resistance changes the feather’s fall.

Dropping a Feather and a Coin in a Long Vacuum Chamber—Gravity Demonstration - The Action Lab:

Brian Cox visits the world's biggest vacuum | Human Universe - BBC:

📄 Coin and Feather - Jeff Rudd: https://www.sfu.ca/phys/demos/demoindex/mechanics/mech1c/coin_and_feather.html

📄 Falling Feather - Exploratorium: https://www.exploratorium.edu/snacks/falling-feather

• Replace the feather with a light object such as a packing peanut or small piece of paper.
• Demonstrate with partial evacuation to show the gradual effect of reduced pressure.
• Compare the classroom version with a video of Apollo 15’s feather-and-hammer drop on the Moon.
• Record the experiment with a slow-motion camera for clearer viewing.

• Only trained individuals should handle vacuum equipment.
• Rotate the tube smoothly to avoid the feather sticking to the walls.
• Ensure the seals and connections are secure to prevent sudden leaks.
• Do not use fragile glass tubing; plexiglass or acrylic is safer.

• Why does the feather fall more slowly in air but not in a vacuum? (Air resistance slows it, but in a vacuum only gravity acts.)
• Why doesn’t the heavier coin fall faster than the feather? (Gravity pulls harder on the coin, but its larger mass resists acceleration equally, so both accelerate at the same rate.)
• How does this demonstration connect to Galileo’s experiments and the Apollo 15 mission? (It confirms that without air resistance, all objects fall equally fast regardless of mass.)
• What is terminal velocity, and how does it explain the feather’s slow fall in air? (It is the speed at which air resistance balances gravity, preventing further acceleration.)