2. Shrinking balloons hydrogen air After 1 week

3. Shrinking balloons 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.

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

5. Diffusion After Gas and gas 10 minutes Cover slip Brown gas

6. Diffusion After Liquid and liquid 2 days Blue liquid water

7. Diffusion After Solid and liquid 5 days Blue crystal water

8. Diffusion After Solid and jelly 1 week Blue crystal jelly

9. Solid, Liquid and Gas Gas Solid Liquid

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

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

12. Expansion and Contraction 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.

13. Expansion and Contraction 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.

14. The bimetallic strip Heat the bimetallic strip

15. The bimetallic strip bends

16. 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.

17. Compression compressed Solid

18. Liquid compressed

19. Gas compressed

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

21. The water cycle. steam (gas) water (liquid) ice (solid) gas solid liquid evaporation condensation meltingfreezing liquid

22. Density 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.