All About Sink and Float

Try this experiment: fill a small tub with water. Gather a few materials from around your house like a paper clip, a penny and a wooden block. Which objects do you think will sink? Which will float? Will the bigger objects sink, while the smaller objects float? Place the objects on the water and find out. Were you right? It seems logical that bigger objects should sink while smaller objects float, but this isn’t always true.

According to Archimedes’ Principle, if the weight of the water displaced is less than the weight of the object, the object will sink. However, if the weight of the water displaced is equal to or greater than the weight of the object, the object will float.

Whether an object sinks or floats depends on its density. Everything is made of molecules. Molecules are tiny particles that can only be seen with a microscope. Some objects have molecules that are packed closely together. Others have molecules that are packed more loosely. This is density. Objects with tightly packed molecules are denser and sink. A paper clip or a penny is dense. Objects with more loosely packed molecules are less dense and float. Wood, cork or sponges float.

Fun Facts about Sink and Float for Kids

Liquids vary in their density too. Try mixing corn syrup, oil and water together. The corn syrup sinks to the bottom because it is the densest. The water is in the middle and the oil floats to the top because it is the lightest.

The shape of an object can also determine if it would sink or float. A ball of clay sinks right away. However, if you flatten the clay out into the shape of a raft, it floats.

Objects filled with air also float.

Sink and Float Vocabulary

Logical: makes sense

Molecules: tiny particles in objects

Dense: how tightly compacted the molecules are

Vary: differ