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Behaviour of matter

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Expansion and contraction

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.
  • Metal parts can be fitted together without welding using shrink fitting. The animation shows how this works.

Expansion and contraction in metal

Metal rod and metal disc with hole. The rod is too big for the hole

The rod is too big to fit through the hole.

bridge expansion joint

Bridge expansion joint

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 take up more room.

  • The particles in a gas move more quickly in all directions when it is heated, and take up more room.

Compares particles in a solid when cold and when hot. When the particles are cold, they are closer together and vibrate less. When they are hot, they vibrate more and are further apart

The particles in a solid vibrate more and take up more room when the solid is heated

Activity

Behaviour of matter activity

Under pressure? See what happens when you cool down.

Play

Elemental

Can you conquer the elements?

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