Why does it float? ? Exploring the Concept of Density

Summary
The lesson consists of a discussion of the concept of density together with a few easy experiments. This is a difficult concept for young children to grasp so the demonstrations are an important part of the lesson.

Objectives
• The children will understand and be able to explain the concept of density.

Suggested Grades
3rd Grade
4th Grade

Excerpt
Activity A should be used as a group activity as facilitated discussion is the best way for the children to internalize a concept. Activity B is an individual activity, providing the opportunity to use the information gained in the lesson.

Reading/Discussion:

Try tossing a small stone and a branch into a stream. Which one floats and which one sinks? Although the stone is smaller and weighs less than the branch, it quickly sinks to the bottom. Why?

It is the density of the object and not the weight that makes it float or sink. The density of an object depends on how much mass (stuff the object is made of) is in the volume (size) of the object.

For example, a slice of bread has quite of lot of air in it, so it is not very dense. If you try, you will find that a slice of bread will float quite nicely in a bowl of water.

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