Category Science

               Gravity is the force that holds us on the Earth. It is also the force that keeps the Earth from flying off into space as it orbits the Sun. The larger the mass of any object the more it attracts other objects with the force of its gravity. The Sun’s gravity helps to pull the Earth’s oceans, causing tides.

               Astronauts in space experience zero gravity, because they orbit the Earth so quickly that the effects of gravity are neutralized. The Moon is much smaller than the Earth, and so it produces less gravity. Astronauts on the Moon weighed only one-sixth of their normal weight on the Earth, even though their body mass remained the same.

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               Rainbows are formed when sunlight falling on raindrops is split into the different colours of the spectrum (range) of light. Sunlight is really a mixture of all the colours of the spectrum: red, orange, yellow, green, blue, indigo and violet, but our eyes always see them as ordinary white light.

               When a beam of light passes at an angle through a curved transparent surface, such as a raindrop, the beam is bent when it emerges. The different colours of light are bent by different amounts, so the white light is split into the colours of the spectrum. This effect can also be seen when light passes through a piece of glass cut at different angles, such as a prism.

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               Infrared radiation, or heat, is a form of electromagnetic energy that is not visible to our eyes. The wavelength of infrared radiation is greater than that of visible light, but much shorter than the wavelength of microwaves. All forms of heat are based on infrared radiation. Infrared photography allows objects to be seen in the dark. It uses cameras that are sensitive to infrared radiation and so they can detect warm objects in the dark.

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               Microwaves are a form of radiation. They can pass through things that would block ordinary radio waves, such as rain and fog. Microwaves can also be focused and sent in a narrow beam, making them very useful for transmitting radio messages over long distances. Microwaves are widely used to transmit television signals to and from orbiting satellites in space, and they are also the basis on which modern mobile telephones work.

               In radar, a beam of microwave energy scans the target area and bounces back signals, producing a picture of the object. Microwaves penetrate the food in a microwave oven, causing the molecules to move about very rapidly. This rapid movement generates the heat that cooks the food.

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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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