Category Science & Technology

Forms of Energy

How do we measure temperature?

               Temperature is a measurement of the amount of heat that is stored in an object. It is measured against a scale in either degrees Celsius (°C) or degrees Fahrenheit (°F) on a thermometer. The Celsius scale starts at the freezing point of water (0°C) and measures the boiling point of water at 100°C. The centre of the Sun probably reaches an incredible temperature of 150 million °C.

               The absolute minimum temperature possible is —273°C, or absolute zero, where it is so cold that molecules and atoms stop moving altogether. More ordinary temperatures are measured using thermometers that contain a liquid such as mercury or coloured alcohol. Other thermometers use electronic sensors or the expansion of a metal coil to turn an indicating needle.

 

 

 

 

 

 

 

 

 

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Where does the Earth’s energy come from?

 

               There is a basic law of physics that says that energy is never created or destroyed; it is simply transferred from one place to another or from one form of energy to another. So all the energy that exists today has been around since the formation of the Universe.

               The Earth’s energy comes from heat trapped inside the Earth when it was originally formed, or from energy radiated out from the Sun. We cannot make energy, but we can extract it from coal, oil, fast-flowing rivers, nuclear fuel and various other sources. Even the wind can supply us with a source of energy.

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Forms of Energy

What is light?

               Light is a form of electromagnetic energy. It is produced by electrons that have gained extra energy from another source. This energy can be given off as heat or light. Light travels in waves of energy that consist of very tiny particles called photons. Atoms emit (give off) photons when heated to a high temperature. The extreme heat causes the atoms to collide with each other, and the extra energy is given off as light. The amount of energy released determines the colour of the light. The hotter an object, the more high-energy blue light is produced. As the object cools, the lower energy produces red light. When metal is heated to white hot, it gradually becomes red as it cools.

 

How fast does light travel?

               The speed of light is the fastest speed known — light travels through the vacuum of space at 300,000 km per second. Nothing else can travel at this speed, and the theory of relativity, conceived by Albert Einstein, says that nothing can even approach this speed. This means that travel to the stars will not be possible, because it would take hundreds of years to reach them.

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Natural Properties

 

What are acids?

               Acids are a group of chemicals with very similar properties. They all have a very sour taste and are capable of burning the skin, although some are much more powerful than others. Many metals will dissolve when they come into contact with acids. This is because acids can release hydrogen ions when they are dissolved in water. Strong acids such as hydrochloric, sulphuric and nitric acids release many hydrogen ions, so they react very fiercely with many substances. Acetic acid, which is an ingredient of vinegar, releases only a limited number of ions and is not a strong acid. This is the reason why it can be used safely in our food.

 

 

 

How can we identify acids and alkalis?

               Dyes called indicators show very quickly if a substance dissolved in water is acid or alkaline. One of these dyes is litmus. If a piece of paper impregnated with litmus is dipped into a solution, it immediately turns red if the solution is acid. If the solution is alkaline, the litmus turns blue.

               A similar dye is present in vegetables such as red cabbage and beetroot, and this dye changes colour in the same way during cooking. If your tap water is hard (alkaline, because it contains dissolved lime), the vegetables will be coloured a deep purplish-blue. Red cabbage and beetroot are often pickled in vinegar, as the acid in vinegar gives them an attractive deep-red colouration.

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Natural Properties

 

Why does my breath ‘steam’ in cold weather?

               When water boils the steam it produces is not visible while the water remains at boiling point. As the steam cools it forms tiny droplets of water, making it look cloudy. This is called water vapour, which is what you see when your breath ‘steams’ in very cold weather. Explorers in the Arctic and Antarctic find that water vapour condenses and freezes to form ice around their nostrils and mouth.

 

 

 

What happens when iron rusts?

               The reddish powdery rust that forms on unprotected iron and steel is the result of a process called oxidation. It takes place when the metal reacts with oxygen from the air and water. Both air and water are needed for rusting to take place. This form of rusting eats into the metal until it collapses into scales and dust of iron oxide.

               When aluminium is cut it oxidizes very quickly, but the newly formed layer of aluminium oxide prevents exposure of the metal to more oxygen. The aluminium oxide stops the process of oxidation, so the metal remains bright and shiny.

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Natural Properties

What happens when a liquid boils?

               When a liquid is heated, at a certain point it begins to change to a gas, or vapour. This happens because at high temperatures the molecules in the liquid move faster, until they escape into the air. Light molecules escape more easily than heavy a molecule, which means that heavy, thick liquids only boil at very high temperatures.

               The boiling point of a liquid depends on the air pressure. The pressure becomes lower at altitude, so high up on a mountain slope; water boils at a much lower temperature than normal. Water boils at 100°C at sea level, but at only 72°C at an altitude of 3,048 m.

 

What is evaporation?

               Evaporation happens when a liquid or a solid changes to a gas. It is a similar process to boiling, because it involves the molecules of a liquid passing into the air. The process of evaporation is much slower when the air above the liquid is already full of molecules of vapour. For example, water will evaporate only very slowly on a warm, damp day when the air is already saturated with water vapour.

               As a liquid evaporates it loses heat energy, making it cooler. This is the principle on which refrigerators and air conditioners work. Evaporation of water from the seas and land produces water vapour in the form of clouds, which eventually drop water back onto the Earth’s surface as rain.

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