Try the Beat the Heat experiment

Before you begin

• Use the safety checklist to help you plan and risk assess your activity. There's also more guidance to help you carry out your risk assessment, including examples.
• Make sure all young people and adults involved in the activity know how to take part safely.
• Make sure you’ll have enough adult helpers. You may need some parents and carers to help.

Planning and setting up this activity

• Always stay sun safe by using sunscreen, wearing hats and sunglasses, staying hydrated, and having lots of rest breaks in the shade or indoors. Use NHS sun safety guidance and our hot weather guidance.
• Make sure to use child-safe, waterproof digital thermometers in this experiment.

Running this activity

1. Gather everyone together and explain you’ll be doing a science experiment to learn how colours can make something hotter or colder.
2. Explain that colours can change how hot or cold something feels! The sun sends light in different colours and each colour has its own special wavelength. Some colours, such as red and orange, have longer wavelengths, while colours, such as blue and violet have shorter wavelengths. When light hits an object, the longer wavelengths are often absorbed better by dark colors, such as black. This means dark colours, such as black and dark blue, soak up more sunlight and make things hotter. Light colours, such as white, reflect the sunlight, helping them stay cooler.
3. Tell everyone that you’re going to use four bottles of water and test how different colours can change the temperature of the water.
4. In small groups, fill four empty bottles with the same amount water.
5. Each group should wrap coloured paper or card around their bottles, then secure them in place with masking tape. One bottle should be wrapped in black paper, one bottle in white paper and the other two bottles can be any two different colours that the group choose.
6. When they’ve wrapped the bottles, someone in each group should measure and write down the ‘before’ temperature of the water in each bottle. 
7. Ask everyone what they think will happen to the water bottles. You can let a few people share their answers if they’d like to. 
8. Now, place all the bottles close together in direct sunlight. Make sure that each group’s bottles are placed in the same area, so that they’re exposed to the same amount of sunlight.
9. Next, set a timer for 20 minutes. You could use this time to tidy up or to play a game.
10. After 20 minutes has passed, each group should go their bottles and use a digital thermometer to measure the water temperature.. Write down the results next to the ‘before’ temperatures.
11. When you’ve got the results, move the bottles inside (or into a shaded area) and allow them to cool down.
12. Gather everyone back together and ask them what their results show. Darker surfaces absorb more energy (light and heat) than light surfaces, so the water in the bottle wrapped in black paper should have become hotter than the one with white paper, because the light bounces off the white paper, but is absorbed and changed into heat by the black paper.
13. Ask everyone if they can think of anything else that might have made the bottles warmer or colder. For example, windy areas can cool down the bottles faster, while sheltered spots keep them warmer. Some other factors might be if any bottles were in shaded areas and the surfaces they were placed on. Dark surfaces, such as grey tarmac, get hotter than light-coloured surfaces. So, bottles on dark surfaces might have warmer water.
14. After the bottles and water have cooled, remove the masking tape and paper, then recycle the paper. You can use the water to water plants, then recycle the bottles.