Expansion & Contraction L/O :- To understand expansion and contraction, and to be able to explain this using particles

Why do you think javelin measuring tapes are not made from metal?

Look at the ball and ring - the ball can pass through the ring easily But… when the ball is heated it cannot pass through the ring! Why do you think this happens?

When the ball is allowed to cool, it suddenly passes through the hoop again Also, a heated glass rod will shatter if placed into iced water Why does this happen?

Expansion & Contraction Substances expand (get bigger) when they are heated up The particles stay the same (the number of particles + their size is the same) But they gain energy, start to move more and spread out so they take up more room Substances contract (get smaller) when they are cooled down They have less energy, so they move less, and move closer together so they take up less room Substances contract (get smaller) when they are cooled down They have less energy, so they move less, and move closer together so they take up less room Do you think expansion and contraction happens in solids, liquids and gases?

Copy out the particle box of a substance Then draw out what happens to the particles when they are a) heated; and b) cooled CoolingHeating

Problems & Uses Expansion of substances can be both useful, and cause problems for designers and engineers - can you think of any? Problem - bridges expand in the summer, and need special joints to stop them bending out of shape Concorde (the supersonic plane) expanded when it was going at very high speed by ~30cm! Thermometers use liquids which expand when they get hotter, and contract when the get colder - very useful for us to measure heat! Expansion joint in a bridge At very high speed friction causes a great deal of heat - this expands the plane in a variety of areas

Revision Try this online test: - Click to try a test and check your understanding so far