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Solids, liquids and gasses have physical properties. The way they behave is
affected by heating and cooling. We will also look at pressure and diffusion in
Substances expand or get bigger when they are heated up. They contract or get
smaller when they are cooled down. This property can be useful.
Thermometers work because the liquid inside them expands and rises up the
tube when it gets hotter.
Materials expanding and contracting can also cause problems. For example,
bridges expand in the summer heat and need special joints to stop them bending
out of shape.
What do the particles do?
When substances expand or contract, their particles stay the same size. It is the
space between the particles that changes:
The particles in a solid vibrate more when it is heated, and take up more room.
The particles in a liquid move around each other more when it is heated, and
takes up more room.
The particles in a gas move more quickly in all directions when it is heated, and
take up more room.
The particles in a gas move quickly in all directions, but they don't get far before
they bump into each other or the walls of their container. When gas particles hit
the walls of their container they cause pressure
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Heating increases pressure
If a gas is heated up, its particles move around more quickly. They hit the walls of
their container harder and more often. This increases the pressure. Sometimes
the pressure gets so great that the container bursts.
This is why balloons and tyres burst if you blow them up too much. It's also why
deodorant spray cans carry warning signs to tell you not to leave them in the
sunshine. If they get too hot they explode.…read more
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Diffusion does not happen at all in solids because the particles in a solid can only
vibrate on the spot, rather than being able to move from place to place.…read more