Buoyancy can be really tricky to understand, our easy experiment will help you to understand why some things float and others sink. Plus, you get a treat at the end of it!

You will need:

• A bucket or tub
• Water
• Can of pop
• Can of diet pop

Method:

• Fill the bucket with water
• Make a prediction, will the can of pop sink or float?
• Drop the can of pop into the water – what happens?
• Make a second prediction, will the can of diet pop sink or float?
• Drop the can of diet pop into the water – what happens this time?

The science bit:

When an object is placed in water there are two forces working upon it in opposite directions. Gravitational force pulls the object down while buoyant force pushes it upwards. Gravity pulls the object down with a force equal to the weight of the object while buoyant force pushes it upwards with a force equal to the weight of the water that the object displaced. If the object can displace a volume of water that equals (or is greater than) the weight of the object, then it will be buoyant and float. Think about your cans, what is different about them? That’s right- one is full of sugar! The added sugar means that the weight of the can is greater than the volume of water it is displacing, so it sinks.