It floats, it sinks

Angélique Boissonneault has a Bachelor's Degree in Biological Science. She has worked in a laboratory and tested her knowledge. She has taught Math, Chemistry, and Physics. She has also developed a simplistic and innovative approach designed to introduce young children to scientific experiments, old and new. She created her friend Globule. This character is sometimes red, and sometimes white. He guides little ones through their scientific experiments and discoveries. It is clear to see Angélique is passionate about children and science. Globule's Approach.

Globule wonders...

Why do some objects float and other objects sink?

Experiment: It floats, it sinks

Material:

A large container filled with water
A cork
A Lego block
A pebble
A coin
A plastic spoon
A metal spoon
A nail
A rubber ball
A piece of cardboard
A piece of wood
Modeling dough (one piece rolled into a ball, another piece shaped like a bowl)

Manipulations:
1. Put all the objects your daycare worker selected for the experiment on the table.
2. Choose one and drop it into the water. Does it sink or float?
3. One at a time, place the objects in the water until there are none left.
4. As you go along, sort the objects into two piles, the objects which float and the objects which sink.
5. Look around for other objects you can experiment with.
6. Try to guess the result before dropping the objects into the water.

Explanations:
There is no rule as to which objects float and which objects sink. You probably noticed that some objects are big but still remain at the surface while other objects are very small but sink to the bottom. Some very heavy objects float (large ships) and light objects sink (a penny). The size or weight of objects does not determine whether they float or sink. The two characteristics must be considered together. The shape of an object plays an important role in regards to its buoyancy. The modeling dough rolled into a ball sinks whereas the modeling dough shaped like a bowl with thin sides, floats. Incredible isn't it?

Source: http://www.educatall.com/page/144/It-floats--it-sinks.html