Balloons and air density

Air has many interesting characteristics. It flows and spreads into spaces that are not already occupied. Air can be compressed, and it can also expand.

This activity enables students to observe how the same amount of air can take up different amounts of space depending on the temperature (energy) of the air molecules.

Investigating air density and volume

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Air expands when heated and increases the pressure in a closed space, causing the balloon to inflate. When the heat is removed, air molecules contract and take up less space, causing the balloon to collapse.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Science capabilities and key competencies

The activity supports the development of the science capabilities and competencies as students:

• draw diagrams to show their thinking

• engage in discussion with peers using evidence to support their position

• critique their own ideas and/or the ideas of others in terms of their validity and applicability.

Throughout the discussion, teachers are encouraged to support critical student thinking and use questioning to develop increased use of evidence and scientific reasoning. Students may also develop questions for research or to check their thinking and understanding.

In this activity, students explore the relationship between air density and volume by observing how air in a bottle expands when immersed in hot water and then contracts when the bottle is placed in cold water.

By the end of this activity, students should be able to:

• draw a diagram showing what they observed during the activity

• use the diagram to provide supporting evidence for their explanation of the phenomena

• begin to understand that heat is a form of energy and that molecules with more energy occupy more space

• begin to understand that increasing volume does not always equate to more particles of matter.

Download the Word file (see link below).