In this topic we are learning to: z Investigate the expansion and contraction of substances with heat. z Review examples of the expansion and contraction of solids in the real world.
Expansion and Contraction
Adding or removing heat from substances has different effects. In general: z When a solid, liquid or gas is heated it expands. z When a solid, liquid or gas is cooled it contracts. Water is an exception, as it begins to expand below 4 °C.
Fig. 19.6.1
An expansion gap in a railway line
We can see the expansion and contraction of substances in a number of places: z There are expansion gaps on concrete roads. Expansion gaps are made of a soft substance, such as tar. When concrete slabs get hot, they expand and squeeze the soft material to stop the road from cracking. Steel railway lines also need expansion gaps.
z If metal bridges get hot, they can expand by up to one metre. They are built with expansion joints to stop this happening.
A student set up the apparatus in Fig. 19.6.4 to test the hypothesis: ‘Liquids expand when heated and contract when cooled.’
1. The student places the flasks into the hot water at the same time. Predict what happens. Explain why you have made this prediction.
2. Set up this apparatus in class and carry out the investigation. Record your observations.
3. Explain why your predictions did or did not match your observations.
4. What does this tell you about the expansion and contraction of the different liquids?
342 342 Water Fig. 19.6.4 Paraffin oil Hot water
z The inside of an iron contains two strips of metal attached together. This is called a bimetallic strip. When these strips are heated, they expand at different rates and bend. This keeps the temperature of the iron regular.
Bimetallic strip
Fig. 19.6.3 The bimetallic strip in a clothes iron
