You might wonder how a cargo ship
weighing a quarter million tons can float in water,
but a paperclip, like this one, sinks.
Well, it has everything to do with buoyancy.
Buoyancy is the ability of something to float in a liquid. 
And it has to do with two things.
The first is density.
Density is how heavy something is
 relative to how much space it takes up.
For example, a bowling ball and a volleyball 
take up about the same amount of space.
But the bowling ball is a lot heavier than the volleyball because the volleyball is full of air.
So we can say that a bowling ball is 
a lot more dense than a volleyball.
Usually, objects that are more dense than the liquid 
they are floating in will sink to the bottom,
but that doesn't explain why large objects
made of really dense materials,
such as cargo ships, are able to float so easily.
This brings up the second thing we need to understand.
A really long time ago, a man 
named Archimedes figured out that
every time you put something in water, it
has to make room for itself.
It does that by pushing aside the water as it gets in.
We're going to use this bin of water to test it out.
If an object like this volleyball is lighter than the 
amount of water it displaces then it floats.
This tends to happen with less dense objects.
But if an object is heavier than the
amount of water it displaces,
or if it's really dense like this bowling ball,
 then it sinks to the bottom.
So back to our cargo ship.
Even though it's very heavy, it's also very large.
And most of it is actually hollow, 
so it's not as dense as we think.
The bottom of the ship is also 
designed to displace a lot of water.
This means that the ship actually ends up being 
lighter than the amount of water it displaces.
And that means it can float.
You can try testing some objects 
yourself to see if they float in water.
Make your predictions first, though. 
The results might surprise you.
I hope you have fun trying this out.
And thanks for watching this 
episode of Things Explained!
