"Floating Objects" Return to list of pracs

Aim: This activity is used to investigate how objects floating in water.

Equipment: The equipment includes...  

Method: Place the ping pong ball and candle into a bowl of water. Press down until each are under water. "How much effort is required to hold the ping pong ball under water compared to the candle?" "Why might they differ?" Connect the spring balance (which measures force) to each object and drop it slowly into the water. Note by how much the value on the spring balance changes. The more it changes the more the water is helping to support the object to float.

Compare all the other objects. Rank them in order of easy to hard.

Background knowledge: Objects float according to their densities compared to water (or another liquid they are in). If you had a number of objects that float all of the same size, the heaviest one will float very low in the water and the lighter one will float very high in the water. The objects that float very high in the water will therefore require more effort to "push" down under the water level than the other objects. It can be considered like a scrum in rugby... if there are more players pushing forward on one side compared to the other, the scrum will move forward in the direction of greater force.

There are much more water molecules pushing up on the ping pong ball than ping pong ball particles pushing down on the water compared to the number of water molecules pushing up on the wood than wood particles pushing down on the water. This is why the wood sits lower in the water and the ping pong ball sits high.