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Trading Places - Liquid Science Magic Trick

A Lesson in Liquid Density

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This is how the liquid swap magic trick looks when you set it up.

This is how the liquid swap magic trick looks when you set it up. Get ready for the two liquids to trade places!

Anne Helmenstine
Take two glasses of different-colored liquids and watch the liquids switch places in the glasses.

Magic Trick Materials

This science magic trick or demonstration can be performed using many different liquids, such as water and wine, water and oil, or water and whiskey. All you need are two liquids that have different densities. If the liquids don't mix (such as water and oil), you will get a clearly-defined separation. Expect some mixing of water with rubbing alcohol or an alcoholic beverage. You can tint a water or alcohol-based liquid with food coloring.
  • two small identical glasses, such as shot glasses
  • water
  • oil or wine or whiskey or rubbing alcohol
  • a thin waterproof card, such as a driver's license

Perform the Liquid Magic Trick

  1. Fill one glass completely full with water.

  2. Fill the other glass completely full with the other liquid you selected.

  3. Place the card over the water glass. While holding the card onto the glass, flip the water glass over and set it and the card on top of the second glass.

  4. Line the glasses up so that they are even and move the card so that there is just a tiny bit of open space at the edge of the glasses.

  5. Over the next few minutes (about 10 minutes for shot glasses), the liquids will exchange places. The alcohol or oil will rise to the top while the water sinks and fills the bottom glass.

How the Liquid Magic Trick Works

Well, obviously not by magic! This is simple science. The two liquids have different densities from each other. Basically, the lighter liquid will float while the heavier liquid will sink. You would see the same result if you had removed the card entirely, except this way is prettier and looks more magical.

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