Secrets of Heat and Cold

Secrets of Heat and Cold — page 1 — Why Are Heat and Cold Important We need heat for so many things in our lives Do you start the day with a warm shower The shower water has to be heated If you have toast for breakfast you need heat to make it If you travel to school by car or bus the engine needs heat to work These examples are just the beginning of the story Most electricity is made in power plants that run on heat 쑼 In a blast furnace iron ore is heated until the iron is molten It can then be separated from the solid slag waste Using Heat Metals must be heated to get them out of the rocks where they are found Plastics are made from oil a process that uses lots of heat Even this book needed heat to make it The paper is made from wood that was cooked in water and chemicals 4

Secrets of Heat and Cold — page 2 — Cooling Down Heat is not always useful Sometimes we need to cool things down Fridges and freezers keep food cold so it lasts longer without going bad Fridges in hospitals keep medicines and vaccines fresh Many engines and machines have to be cooled or they overheat and do not work properly Even people need cooling We sweat to stay cool in hot weather Studying Heat and Cold In this book you will learn some of the amazing things scientists have found out about heat and cold Humans are warmer than their surroundings because mammals generate heat inside their bodies Our bodies produce surprising amounts of heat In just 15 minutes an adult gives off enough heat to boil more than 2 pints 1 liter of water A young person being smaller gives off less heat 쑿 A thermogram is a special picture that shows how much heat an object or living thing gives off Hot areas appear red or yellow colder areas green or blue 5

Secrets of Heat and Cold — page 3 — What Are Heat and Cold Heat is a kind of energy scientists call it thermal energy The hotter something is the more thermal energy it has The boiling water used to make a cup of coffee has a lot more thermal energy than cold water from the tap Cold by Comparison It sounds strange but cold and heat are the same thing Something that is cold has thermal energy as does a hot thing Something is only hot or cold compared to something else When we talk about things being hot or cold we usually mean compared to our bodies An ice cube feels cold because it is colder than the body 쑼 Many of the lights used in theaters and for music concerts have halogen bulbs The filaments wires in these bulbs get very hot about 7,230 F 4,000 C 6

Secrets of Heat and Cold — page 4 — A cup of coffee feels hot because it is warmer than the body However if you compared a cup of coffee to a pot of molten iron you could say that the coffee is relatively cold the molten iron is far hotter 1 2 TRICKING THE SENSES TRICKING THE SENSES This experiment demonstrates how This experiment demonstrates how our senses can be confused about our senses can be confused about whether something is hot or cold whether something is hot or cold You will need You will need glass of iced water take the a glass of iced water take the ice out after cooling the water ice out after cooling the water glass of hand-hot water glass of a glass of very warm water a water at room temperature glass of water at room temperature 1 Put the first finger of your right 1 Put the first finger of your right hand in the glass of hot water and hand in the glass of warm water and the first finger of your left hand in the first finger of your left hand in the cold water Leave them there for the cold water Leave them there for about a minute about a minute 2 Now put one finger then the other 2 Now put both fingers in the in the room-temperature water How room-temperature water Do the does this feel fingers feel the same or different 7 씰 An ice cream is cold but in fact it still has a lot of thermal heat energy

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