How does a heavy metal ship float on water?
Big ships are made of heavy metal… so how do they float? Watch this. The very same metal can be a tight little ball, or a wide open boat. We drop them both in the water. Tap your guess… which one floats — the ball, or the boat? Then watch what the water does!
After you watchHow does a heavy metal ship float on water?
The short answer
A metal boat floats because of its wide, hollow shape, not because metal is light. The open boat shape pushes a lot of water out of the way, and that water pushes back up hard enough to hold the boat on top.
The whole story
How it works
Water always pushes up on things you put in it. The more water a shape shoves out of the way, the harder the water pushes back. A wide, open boat shoves aside lots of water, so the water can hold it up. The very same metal squished into a tight little ball shoves aside almost no water, so it sinks. Same metal, same weight — only the shape changed.
What people get wrong
Many kids think heavy things always sink and light things always float, so heavy metal should always sink. But a wide boat shape floats because it pushes aside lots of water, even though it is made of the same heavy metal as a ball that sinks.
Questions kids ask
If the metal weighs the same, why does the boat float but the ball sinks?
Floating is about shape, not just weight. A wide boat pushes lots of water out of the way, and that water pushes back up and holds it. A tight ball pushes aside almost no water, so the water cannot hold it up and it sinks.
What holds the boat up?
The water itself! Water always pushes up on things. When a wide boat shoves a lot of water out of the way, the water pushes back up just as hard, and that upward push keeps the boat on top.
Keep going
What else makes you wonder?
- Why does ice float on top of a drink instead of sinking?
- Why is it so hard to push a beach ball under the water?