Sink or Float

Anything you can touch is called matter. The amount of space matter takes up is called mass (size). Most of the time, the more mass something has (the bigger something is), the more it weighs…but not always.

For example, A beach ball is bigger than a golf ball, but the golf ball weighs more than the beach ball. Do you know why this is? The reason the golf ball weighs more even though it is smaller is because of density. Density is the amount of matter in an object. There is more matter squeezed into the golf ball than there is the beach ball.

The golf ball has matter inside of it but the beach ball only has air. The amount of density something has also told us if an object will float or not.

The more air something has the easier it floats. Let’s see how this works. But…the water has to be deep enough for an object to be able to push the water down so it can sit or float on it.

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  • A large container such as a five-gallon bucket or plastic storage tub
  • Water
  • 2 oranges
  • Tennis ball
  • Marble or rock about the size of a marble
  • Spoon
  • Empty soda can
  • Butter knife
  • Small craft stick (like one from an ice cream bar)


  • Fill the bucket or storage tub with water
  • Place the tennis ball and the rock or marble on top of the water at the same time
  • Note which item floats and which one sinks
  • Remove these items
  • Place the spoon and empty soda can on the water at the same time
  • Note which item floats and which one sinks
  • Remove these items
  • Place the butter knife and the craft stick in the water at the same time
  • Note which item floats and which one sinks
  • Peel one orange then place both oranges on the water at the same time
  • Note which orange floats and which one sinks


Matter (objects) that contains more air than mass weigh less than the water surface. This lets these objects rest or float on top of the water.

The tennis ball is larger than the rock or marble, rocks and marbles are solid. Tennis balls are hollow and filled with air. The air inside the tennis ball weighs less than the inside of a rock or marble, so the tennis ball floats.

The spoon is smaller and skinnier than the empty soda can. But because the spoon is metal all the way through and the can is hollow (when it is empty), it floats.

The knife and the craft stick are the same shapes. Both are flat and thin. So why did the stick float while the knife sank to the bottom? The stick was able to float because the density of wood is less than the density of the knife.

Look at the peal on the orange. Do you see all the little dimples? Hold a piece of the peal in your hand. Do you notice how lite it is? The dimples in the orange pealing are like little air sacks.

These little air sacks make the orange with the pealing on it float. The peeled orange sinks because it does not have these air sacks to hold it up.


  • Repeat the experiment using different objects.
  • Repeat the experiment using only two or three inches of water. Are your results any different? How are they different?


  • You learned the difference between mass and density.
  • You learned that big objects are not always heavier than small objects.
  • You learned what makes an object heavy or light.
  • You learned that the density of an object decides if that object will float or sink.