Shrinking balloons After 1 week hydrogen After 1

Shrinking balloons After 1 week hydrogen After 1 week air

Shrinking balloons n n The balloons have got smaller so some of the gas they contain has escaped. This means that the balloon must have holes in its surface. Since the gas is escaping it must be made of tiny particles. To escape these particles must be able to move.

Mixing substances n Diffusion is the name for the way in which one substance can spread through another.

Diffusion Gas and gas Cover slip After 10 minutes Brown gas

Diffusion Liquid and liquid water After 2 days Blue liquid

Diffusion Solid and liquid water After 5 days Blue crystal

Diffusion Solid and jelly After 1 week Blue crystal

Solid, Liquid and Gas Liquid Solid Gas

Diffusion n These experiments tell us: Gases Liquids Solids Larger spaces between particles

Diffusion n These experiments tell us: Gases Particles move quickly Liquids Particles move slowly Solids Particles hardly move

Expansion and Contraction n n When anything is heated it expands (gets bigger), and when it is cooled it contracts (gets smaller). Phone wires are hung loosely, so that they will not break when they contract in winter.

Expansion and Contraction n n Railway lines have gaps between them, so that they will not buckle and bend in hot weather. The mercury in a thermometer expands and contracts so that we can measure temperature.

The bimetallic strip Heat the bimetallic strip

The bimetallic strip bends

n n The bimetallic strip is made of two different metals. When the bimetallic strip is heated both metals expand differently. This makes the bimetallic strip bend. The bimetallic strip is used in fire alarms and thermostats.

Compression Solid compressed

Liquid compressed

Gas compressed

Air pressure n n n Air particles move quickly around us. They hit us, and all other objects, from all sides. This force on us is called air pressure.

The water cycle. condensation evaporation gas steam (gas) liquid water (liquid) melting solid ice (solid) freezing

Density n n In dense materials the particles are packed closely together. Density is measured by dividing mass by volume. Water has a density of 1 g/cm 3. Any substance with a density of more than 1 g/cm 3 will sink in water.