My Science School

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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               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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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.

 

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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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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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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               Plastics are synthetically produced materials that are capable of being moulded and made into useful shapes such as bottles and flat sheets. They usually soften under heat and pressure so they can be forced into a mould. Some types of plastic are set into a hard solid form by the application of heat, causing a chemical reaction between the component substances.

               Most plastics are light in weight, are good electrical insulators and are tough enough to have many domestic and industrial uses.

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               Some very light metals such as lithium and calcium can float in water. They also react with the oxygen in water, releasing hydrogen. The similar (but heavier) metals, such as sodium and potassium, generate so much heat when they are dropped into water that the hydrogen they release burns on the water’s surface.

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               When a substance burns, there is a very rapid chemical reaction with oxygen in the air. This reaction generates heat and light, producing a flame. There are other forms of burning too. Some metals burn in corrosive gases, for example. Explosions are a form of burning in which the reaction takes place extremely rapidly, releasing very large amounts of heat.

 

               When sugar is stirred into water, it dissolves and forms a solution. This means that the solid sugar molecules have split apart and become distributed equally throughout the water, so that no particles can be seen. The warmer the water, the more sugar can be dissolved into the solution. There are some molecules that do not behave in this way. Fats and oils, for example, will not dissolve in water — they can be seen floating on it —although they will dissolve in some other types of liquid.

               Solutions are not always liquids. Brass is a yellowish metal that is actually a solid solution containing copper and tin.

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            Crystals are solid substances that have their atoms arranged in regular patterns. Most naturally occurring substances form crystals under the right conditions, although they are not always apparent. Crystals form into regular geometric shapes, and crystals of the same substance or mixture of substances will always have the same regular appearance.

            Crystals are formed from solutions or melted materials. As the solutions evaporate or the melted materials cool, their atoms are forced closer together, producing a crystal. This crystal gradually grows as the process continues. Some crystals grow into complicated and beautiful shapes, which are often brightly coloured.

            Glass forms when melted solid materials are cooled quickly, so that they do not produce crystals. There are many types of glass, but the transparent glass that is most familiar to us is a very useful material. It is resistant to most corrosive substances, and it is a very good electrical insulator and heat insulator. Glass is stronger than most metals, but because it is brittle it shatters easily.

            The most common forms of glass are made from a melted mixture of silica (sand), sodium oxide and calcium oxide. Lead crystal is a form of glass in which the calcium oxide is replaced by lead oxide. The most heat-resistant glass can be made from pure silica.

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            Almost 80 percent of all elements are metals. They can be distinguished from other elements because when cut, they reflect light and appear shiny. Metals also conduct heat and electricity. Most metals are malleable, which means that they can be beaten or moulded into different shapes.

            Most metals react with oxygen in the air, or with other kinds of elements, to form compounds. They are rarely found in the natural metallic state. However, gold is an exception, because it does not react easily with other elements and is often found in its natural state as grains or nuggets. Mixtures of metals are called alloys.

               Mercury is the only metal that is a liquid at ordinary room temperatures. It is a bright shiny colour, and flows rapidly when poured out of a container (this is why it used to be called ‘quicksilver’). Mercury does not stick to glass, so it is used in thermometers to indicate the temperature.

               Mercury compounds are often brightly coloured and were once widely used in coloured paints. However, mercury is an extremely poisonous substance and its use is now strictly controlled. Some other uses of mercury are in the manufacture of batteries and in medicine. Dentists still use a mixture of mercury and silver, in the form of amalgam, to fill cavities in teeth.

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               Mercury is the only metal that is a liquid at ordinary room temperatures. It is a bright shiny colour, and flows rapidly when poured out of a container (this is why it used to be called ‘quicksilver’). Mercury does not stick to glass, so it is used in thermometers to indicate the temperature.

               Mercury compounds are often brightly coloured and were once widely used in coloured paints. However, mercury is an extremely poisonous substance and its use is now strictly controlled. Some other uses of mercury are in the manufacture of batteries and in medicine. Dentists still use a mixture of mercury and silver, in the form of amalgam, to fill cavities in teeth.

Picture credit: google