Lina and Maria are packing for a picnic. It’s so hot outside! I want to take a tub of ice cream, but it’s going to melt before we get there! I wonder if we can prevent that somehow… Ice cream melts because the heat from outside is transferred to the ice cream and raises its temperature above the melting point. How can Lina and Maria keep the ice cream’s temperature low for longer, until they get to the picnic spot?
In their case, most of the heat is transferred through direct contact between the hot air outside, and the cold ice cream tub. This type of heat transfer is called thermal conduction. To keep the ice cream cold, Maria and Lina need to slow down the thermal conduction. In situations like this, it’s useful to know that some materials don’t allow heat to transfer easily. Materials like plastic, styrofoam, glass, wood, and dry fabrics, such as wool or cotton, do not conduct heat well.
The heat transfer through these materials is slower. Such materials are thermal insulators. Wrapping ice cream in these types of materials will minimize heat transfer between the ice cream and the surrounding air, keeping the ice cream cold. So maybe we can wrap the tub of ice cream in our picnic blanket! When I wrap myself in a blanket it keeps me warm, not cold.
Wouldn’t a blanket make the ice cream melt faster? Insulators can be used to keep things either cold or warm, depending on the direction of heat transfer. In the case of ice cream, heat travels from the warmer air, to the colder ice cream. Placing an insulator between the air and the ice cream, prevents the ice cream from receiving more heat, so it stays cold. And on a cold day, your body is warmer than the air, so heat would normally travel out of your body.
But if you wrap yourself in a blanket, it slows the heat transfer and you stay warm. Because insulation can keep heat both in and out, insulating materials can be very useful when building houses. Insulation keeps heat inside during the winter, which helps save on heating costs. And during summer, insulation blocks the outside heat from coming in, so the house stays cooler. House insulation is often made of materials such as foam, or natural or synthetic fibres.
These are great insulators, because they trap tiny pockets of air inside them. Air, even though it can get hot itself, doesn’t conduct heat very well. You notice this if you hold out your hand near a warm object. You can feel that the air warms up close to the object, but just a little further away, the air is usually not warm at all! Air is a great insulator.
Many animals use air to prevent heat loss in cold environments. Many mammals are covered in hair or wool, which can trap air close to the body, minimizing heat transfer. Similarly, birds can fluff up their feathers to get the same effect! People use these methods to stay warm too! Our winter jackets are often made of down or synthetic fibers.
Or we layer our clothes — the more layers, the more air is trapped in between them, and the harder it is for heat to escape... Wait, I found a cooler, this might be an even better insulator than a blanket. Great idea! And let’s take some extra layers of clothes, in case it gets cold this evening!