Investigate why boats float

In this activity learners will learn what is meant by density. Learners will perform an experiment to see whether modelling clay moulded into different shapes either sinks or floats. They will discuss why this happens and how the principle demonstrated allows boats to stay afloat.

This is one of a series of resources produced in association with Fairfield Control Systems that are designed to allow learners to use the theme of waterways to develop their knowledge and skills in Design & Technology, Mathematics and Science. This resource focuses on understanding density and, through practical measurement, working out which materials are low and high density, and which will therefore float or sink.

Activity: Investigate why boats float

The teacher will first explain the key concepts of density, volume and mass, and their link to Archimedes. The teacher will then demonstrate the steps shown in the teacher presentation to manage the water level and mould the modelling clay into a boat shape, before discussing the results of the activity with learners asking questions such as how much water was displaced for the different shapes and why did the different shapes float or sink?

This activity can be simplified (particularly for less able students) by providing a mould to make the boat shape from the modelling clay or by pre-measuring the mass of modelling clay used.

As an extension students could try adding small items into the modelling clay boat. How much weight can it carry before it sinks? Calculate the density of the ball and the boat shape made from modelling clay. 

This activity is designed to take between 40-70 minutes.

Tools/resources required

• Bowls and trays
• Science beakers/Measuring jugs
• Weighing scales
• Water
• Modelling clay

The engineering context

The waterways (including their protection, maintenance and control) is an excellent context to explore opportunities that working in the engineering industry presents. For example, constructing locks, building narrowboats or making and maintaining boat lifts.

Engineers often make models of working systems to test how they function. For example, a crane designer will make models of different crane designs to see which structures can provide the best support and which designs can lift the heaviest object.

Suggested learning outcomes

By the end of this free resource students will be able to understand how Archimedes’ principle works; that is two things are the same size, the one that is denser is heavier; and how boats use the Archimedes principle to stay afloat.

Download the free Investigate why boats float activity sheet below!

All activity sheets and supporting resources are free to download, and all the documents are fully editable, so you can tailor them to your students’ and your schools’ needs.

The activity sheet includes teacher notes, guidance, useful web links, and links (where appropriate) to the national curriculum in each of the four devolved UK nations; England, Northern Ireland, Scotland and Wales.

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