Stepping Into Science: F for Float and Sink

3 min read

Stepping Into Science is a series where we explore exciting science concepts from A-Z. There will also be activity ideas accompanying each post to extend your child’s learning.

Do all light objects float? Do all heavy objects sink? 

This activity is a great beginner science experiment that will introduce toddlers and preschoolers to density and buoyancy.

This float or sink experiment will encourage the child to predict and observe. Through their observations, they will discover that buoyant objects float and dense objects sink. The mass of the objects does not determine their ability to float or sink.

What makes an object float (or sink)?

Children may be likely to mention that objects sink or float due to their size and weight. If that is true, then how is it possible for a tiny grain of rice to sink, while a huge cruise ship is able to float?

You can then explain that an object sinks, or floats based on its density in relevance to the water.

Whether an objects floats or sinks in water depends on its density (image source:

Density refers to the mass of an object is in comparison to the space that it occupies. For example, a heavy ship occupies a large amount of space, making it less dense than water. In comparison, a needle can be light but occupies a small amount of space. This makes the needle more dense in water, and it sinks.

1. Gather all the things in a box. You can also turn this part of the activity into a scavenger hunt by giving the list of items to the children and ask them to search around the house.

2. Fill the container with water.

3. Before adding the objects into the water, ask the children to predict which objects they think will sink and which objects will float. You can write down their predictions in the chart below

4. Invite the children to drop the objects, one by one, into the water and observe what happens.

5. Before explaining why objects sink or float, ask your children why they think an object sinks or floats.

6. Allow the children to repeat the activity as many times as they please. This will help to reinforce learning and have them reap the benefits of play-based learning. 

Written by Norain Binte Hassein, HOD Science, West Spring Primary School
Illustrated by Regina Yan


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