Warm and Cold: Expanding Air

As air gets warm, the air molecules have more energy and move around more, taking up more space. As the warm air expands, it becomes less dense (see ‘Floating and Sinking: Looking at Density’) than the cold air, so rises up and floats above the cold air. Water acts in …

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Action and Reaction: Balloons in Flight

Sir Isaac Newton was born in 1643 and died in 1727. He was a physicist, mathematician, astronomer, biologist and chemist. Newton developed three laws of motion, which described how things move in response to forces (things like ‘pushes’ or ‘pulls’). Newton’s Third Law states that, “to every action there is …

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Pulling and Pushing: Magnetic Attraction

Magnets are attracted to some metals, and can attract and repel each other. The earth has a magnetic field, and so magnets can be used to find directions. Magnets and Magnets Magnets attract or repel other magnets. Put a bar magnet on a table and move the end of another …

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Friction: Keeping Warm and Keeping Rolling

Friction is the force that acts between two moving surfaces and tries to stop them moving. Friction can be between two solids, a solid and a liquid, or a solid and a gas. The amount of friction between solid surfaces depends on the weight of the objects and the roughness …

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Floating and Sinking: Looking at Density

Density describes how much something weighs relating to its size. For example, a cubic centimetre of cork weighs less (is less dense) than a cubic centimetre of lead (which is more dense). Density explains why some things float on water and some sink – if something is less dense than …

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Static Electricity: Making Things Stick

Atoms (the tiny building blocks that make everything) contain protons, which have a positive charge, and electrons, which have a negative charge. Some electrons are fixed onto the atoms quite loosely, and can come off quite easily when two different materials are rubbed together, and transfer from one surface to …

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Detecting Fake Silver: Conductivity of Metal

Heat travels in three different ways – conduction (heat travelling through a solid), convection (heat travelling through liquids and gases) and radiation (heat travelling through empty spaces). Detecting Fake Silver: Heat Conductivity in Metal To find out if a spoon is real silver, put it in a mug with a …

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Bending Light: Disappearing Glass Bowl and Bending Pencil

As light passes through transparent objects, it bends. This can create optical illusions like disappearing bowls, bending pencils and mirages. This is called refraction, and is useful in magnifying glasses and spectacles. Disappearing Glass Fill a glass bowl with cooking oil (it can still be used afterwards) and gently lower …

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