Hot Air, Cold Air Science Activity

This Hot Air, Cold Air Science Activity is a great experiment to watch the effects of hot air and cold air on a balloon. 

This activity is a great opportunity for kids to talk about what they can see and why it is happening.  Kids will absolutely love this activity and will see, first hand, what effects hot and cold air has on a balloon.

What you will need?

You will need two containers, one filled with hot tap water and the other with ice and cold water.  You will also need 1 balloon and a 1.25litre (or 2litre) plastic soft drink bottle.  The larger the bottle the more room the air has to push up and expand.

Please do not use boiling hot water for this activity.  Hot water from the tap will effectively work for this activity.

Let’s Play

During the following steps of the activity, provide children with the opportunity to predict, ask questions and discuss ideas.

1.  Blow the balloon up to stretch it and help make it more flexible and let the air out.
2. Place the balloon over the mouth of the empty plastic bottle.
3. Stand the bottle in the centre of the container filled with hot water. Wait a few minutes and notice the balloon start to inflate and expand.
4. Remove the bottle from the hot water and place it in the container with cold water and ice. Wait a few moments and notice that the balloon starts to deflate and contract.
5. Repeat step 3 and 4 again….it’s amazing!

Let’s Learn

Science activities and experiments are a great opportunity to make connections between real life experiences such as the hot air balloon ride.  It encourages children to ask questions and promote scientific thinking such as making predictions, observations, comparison, reasoning, data gathering, experimentation and evaluation.

Other Learning Opportunities

• Language development: Using descriptive words to express ideas and opinions.
• Cause and Effect
• Concentration

What is happening?

When the air inside the plastic bottle is warmed, it expands and needs more space, therefore it stretches out the balloon.  When the bottle is transferred to the icy cold water, the air is cooled; it contracts and needs less space, so the balloon deflates.  The mass of air remains constant inside the bottle, so this shows that the warm air requires more space and is less dense than cool air.