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Science at Home

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Cup Drop

Learn about types of energy in this fun and puzzling experiment. Can you get four eggs to drop into cups?


  • Four eggs or balls 
  • Four paper-towel or toilet-paper tubes
  • Four plastic cups
  • Thick piece of cardboard
  • Broom
  • Water
  • Sheets or towels (optional)


  1. Fill each cup halfway with water.
  2. Place them on a table, near the edge, in the shape of a square. (You might want to cover the area below the table with a sheet or towels, in case of mess.)
  3. Put the piece of cardboard on top of the cups.
  4. Stand the tubes up on the cardboard. Each tube should be directly above a cup – check your setup from all sides to make sure the tubes and cups line up.
  5. Put one egg on the top of each tube. Think about how you can get the eggs to drop into the cups. What different ways might work?
  6. Try using the broom as a tool to help the eggs drop. Here’s how: Stand close to the edge of the table near the piece of cardboard holding the tubes and eggs. Use your foot to press the broom’s bristles to the floor. Pull the broom handle away from the table about 45 degrees and let go, aiming for the piece of cardboard. What happens when the broom handle hits the cardboard? (Hint: Let the cardboard hang off the edge of the table just a bit, so the broom handle hits the cardboard and not the table.)

What's happening?

The cup drop illustrates the transfer of potential energy to kinetic energy. The potential energy from the eggs transfers into kinetic energy after an outside force (gravity) acts upon the egg.

This activity also demonstrates Newton’s first law of motion (inertia), which says that an object at rest tends to stay at rest, while an object in motion tends to stay in motion unless acted upon by an outside force. The eggs stay at rest until acted upon by an outside force. Gravity is the force that that pulls the eggs down once there is no longer another outside force (the piece of cardboard) to hold them up.


Discuss these guiding questions:

  • What are the possible ways to make the eggs drop into the cups?
  • Where is the transfer of energy in this activity?
  • What is the role of inertia in this activity?
  • How does this activity relate to the magician’s table cloth trick?


An object stays still or moving unless an outside force is applied to it

Kinetic energy
Energy from motion

Potential energy
Stored energy that transforms into kinetic energy