31. How to keep objects warm

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How to keep objects warm

Some objects need to be kept warm - for example, teapots or animals in cold climates. To do this, the rate of energy transfer via conduction, convection and radiation from the object to the surroundings must be minimised. We want to keep the heat energy IN the object and not lose it to the surroundings.

What design features will help an object keep its heat?

Firstly, the object's material should be a good insulator (a poor conductor). Trapping air in pockets (e.g. an animal's fur, or a wooly jumper) is a great way of surrounding an object with a good insulator and therefore reducing heat transfer by conduction.

The shape affects heat transfer. To stay warm, the object should have a low surface area. This is why a polar bear's ears are quite small - to reduce heat transfer by convection.

A bright colour and a shiny surface will reduce heat transfer via radiation. A polar bear is white for this reason (as well as for camouflage in snow). Teapots are often a shiny mirror finish to keep the tea hot.

Finally, to keep objects warm it's best if they are kept out of any moving air such as a cold wind. This will reduce heat transfer via convection.

GCSE Keywords: Design features, Rate of heat transfer, Minimise, Material, Shape, Colour, Texture, Trapped air pockets

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