sink or float?

This is a fun experiment to do, because the kids can decide which of their toys/craft supplies they would like to test (as long as they are waterproof). It can be surprising which items will float in water and which items will sink. This is hands-on learning of buoyancy and density!

Part 1: Random objects
What you need:

• large glass/plastic cup or bowl
• items that will sink or float! (ideas: marbles, paper clips, lemon slice with rind off, legos, lemon slice with rind on, plastic toy animals, craft sticks, sponges, small bowls or cups, a balloon filled with air, a water balloon, a feather, a ball of clay, a boat made of clay, boats made of other items like craft sticks, etc.)

Have them guess which items might sink or float ahead of time, and see if they're right!  We used part of the Thames and Kosmos Little Labs Boats for this experiment, but it is not necessary to buy the kit to do this experiment.

Sinking marble.

Floating clay boat.

Floating marble in the boat.

Lego floating.

You can sort the objects by whether they float or sink.

Part 2: Eggs
What you need:

• 1-3 eggs (one for each glass or just keep reusing the same one)
• Three glasses, pitchers, or bowls
• Fill one with regular water
• Fill one with heavily salted water (stir well)
• Fill one halfway with salt water, and keep a small pitcher of tap water on hand

Ask your child what he thinks will happen when he puts the egg in each glass. For the third glass, put the egg in so it will float to the top of the salt water (salt water is more dense than an egg), and then slowly pour the tap water on top. It will keep the egg floating halfway in the glass: