Why Do Some Objects Float While Others Sink?

Why do some things float and others sink? Imagine a bathtub filled with water. If you drop in a small rock, it sinks, but if you put a big boat in, it floats! It’s all about how much water is pushed out of the way when something goes into the bath. A boat pushes out more water than its own weight, so it floats, while a rock pushes out less, and it sinks.

Take the quiz →

Examples

  1. A toy boat floats because it pushes out a lot of water, more than its own weight.
  2. A metal ball sinks in water but floats in mercury because mercury is denser.
  3. A balloon filled with helium floats up because the air it displaces weighs more than the balloon and the gas inside.

Ask a question

See also

Discussion

Recent activity