Experiment: Archimedes’ principle

Everybody knows that once upon a time, Archimedes sat in his bath tub and all of a sudden shouted “Eureka!”. But do you know why he did that?

For this experiment you’ll need:

  • A large glass / jar / jug (which has to be see-through)
  • A small plastic mug (which fits inside your glass / jar / jug)
  • A couple of coins, small pebbles or something else “heavy”
  • An apple (or something else that floats)
  • A non-permanent pen

Fill the large glass with water and mark the water level on the outside of the glass. Then put the little plastic mug inside. Fill as many coins (or other “heavy” things) into the small plastic mug until it sinks. As you are filling coins into the small plastic mug, the water lever rises. Mark  how high the water level is right when there are so many coins inside the plastic mug that it sinks!

Now take all the stuff out of the large glass again. The water level goes back to where it was before.

What do you think would happen if we added all the coins to the large glass directly, without putting them inside the floating plastic cup? Do you think the water level would change? And if it changed, where would it end up relative to the two marks you already made on the glass?

Now try and check whether you guessed correctly!

Then do the experiment again, this time with the apple. What happens?