Salt and Marble Mystery

The secret to finding the cereal box toy

Print this Experiment

Finding the toy surprise in your favorite breakfast cereal is never easy. Most of the time you’re forced to dig through the cereal or dump it out just to find the lousy toy. Stop the digging! Believe it or not, there’s a science to finding the toy surprise. A classic science puzzle will teach you how to make the toy surprise rise to the top of the cereal… without ever opening the box!

Here's What You'll Need

  • Plastic test tube with an end cap
  • Salt
  • Marble


  1. Fill the test tube 3/4 full with salt.
  2. Place the marble on top of the salt.
  3. Seal the end of the test tube with a cap (or a cork). The trick is to get the ball from one end of the tube to the other, through the salt.

One might think that since the marble is much more dense than the salt, it will sink to the bottom when the sand is agitated. The opposite is actually true.

How Does It Work?

Hold the tube vertically with the marble at or near the bottom. As you shake the tube up and down, the marble will actually rise through the column of salt. Each time the tube is jerked upwards, both the marble and the salt move up at the same speed. Because the salt particles are lighter and smaller, they experience greater relative friction than the marble when rubbing against each other. This causes the salt particles to slow down faster. After each shake, more salt particles are packed underneath the marble, until it magically emerges from beneath the salt.

Additional Info

What does this have to do with finding the toy surprise in my cereal?
Use the same technique you used with the marble puzzle to make the toy surprise rise to the top of the cereal. Hold the box vertically and shake it up and down. Each time the box is jerked upwards, the toy surprise moves up through the cereal to eventually emerge from beneath the flakes. To everyone’s amazement, you’ll be able to open the box of cereal and have the toy surprise just waiting for you at the top of the box. That’s physics in action!

Browse more experiments by concept: