What do ships, plastic bottles and sponges all have in common? They all float if you put them on the water! Other items such as keys, an anchor or an orange, with the peel taken off, will sink if you place them in a bowl of water, or on the surface of a lake.
Have you ever wondered why that is?
The answer revolves around something called density.
The first thing you need to understand is that every single thing in the world is made up of teeny, tiny particles, called molecules. These are so small that you cannot see them with your eyes; scientists have to use powerful tools such as microscopes if they want to see molecules up close!
These molecules make up each and everything on the planet – including you!
In some objects, such as your kitchen table, the molecules are jam-packed very close together. Imagine if you were taking the Tube, or in a busy, crowded classroom with lots of other children, all standing very close together and holding hands.
These items have a higher density.
In some other objects, such as water, the molecules are more relaxed. They stand further apart, with plenty of space between them. Imagine when you are getting into a space for PE or exercise, and you swing your arms around to make sure you aren’t too close. That’s what the molecules look like in objects like water or orange juice.
These items have a lower density.
Lets Recap!
It might seem confusing, but basically: some molecules stand super close together, and others are further apart. The distance between them tells us what kind of object they make – is it hard or soft? It also decides the density of the object – this is important in working out if it will sink or float.
Remember: you can’t actually see the molecules, only the object they make! They are invisible to you.
So Why Do Some Things Sink?
Ok, but this doesn’t explain why some things sink, and some things float!
It all comes down to the Gravity – this is the force which keeps us on the Earth and stops us whizzing off into outer space like astronauts. Imagine that you had strings tied to the bottom of your shoes, and someone under the ground was pulling you downwards. Now imagine if that person was sitting right in the centre of the Earth, pulling you downwards! We can give that person a name: Gravity.
There is one other character we need to meet before we understand sinking and floating: Buyoyncy. It is a tricky word for a simple idea: Buoyancy is the opposite of Gravity.
While Gravity is trying to push you down, Buoyancy is trying to push you back up at the same time! This is how things float.
Now…time to try out the experiment in the Creative Garden: can you make your boat float?
