Some objects float because they are lighter than the water they push aside, and others sink because they are heavier.
Imagine you're playing with a toy boat in the bathtub. When you put it in the water, it floats because the boat is not too heavy, and it pushes up some water, like when you splash around and make waves. The water then pushes back up on the boat, helping it stay on top.
Now imagine you drop a big rock into the tub. It sinks right to the bottom because the rock is too heavy for the water to push it back up. The water can’t hold the whole rock, it’s like trying to float with your backpack full of books!
What Makes Something Float or Sink?
- If something is lighter than the water it pushes aside, it floats.
- If something is heavier, it sinks.
It's all about how much water gets moved out of the way and whether that water can push back hard enough to keep the object afloat.
Examples
- A wooden block floats because it is less dense than water.
- A stone sinks because it is more dense than water.
- A boat can float even though it's made of heavy metal.
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See also
- How Does 4 Ways To Stay Underwater Without Floating Up Work?
- Why do boats float, even when made of heavy steel?
- What Causes the ‘Glow’ of a Neon Sign?
- Why doesn't water boil in the oven?
- Why does ice float in water, unlike most other frozen solids?