Sound barrier

The analogy of a boat cutting through water and the waves rippling behind might be helpful to explain what happens to a plane and the sound waves. The “echo” is a good way to explain to younger children how sound travels. How fast does sound travel (varies according to what it is passing through, but for a plane roughly 750 miles or 1,200 kilometres per hour)? What is the sound barrier (below the speed of sound, waves are all round the plane, the pressure forming a barrier in front; once above it, waves are mainly behind)? What happens when a plane breaks through it (there is a “bang” - the sonic boom - as the cone-shaped pressure field hits the earth at low altitude causing damage to buildings, like broken windows)?

Atmosphere

What is air (about four-fifths nitrogen, one-fifth oxygen, plus water vapour and other gases)? Water vapour forms the circular cloud in the picture. What is above your head, as you move up into the sky (five zones: the troposphere, up to four or five miles, then the stratosphere, to about 30 miles, followed by the mesosphere, the thermosphere and the exosphere)? Where do planes fly (only in the first two zones, up to the bottom end of the stratosphere; rocketsgo higher)?

Speed

How fast, roughly, are different forms of travel (walking, 4mph; cycling, 10-20mph; car, 30mph in town, 70 mph on motorway; train, 100mph; jet plane, 500mph; Concorde, 1,350mph; rocket, 18,000mph)? If the distance between London and Leicester is about 100 miles, how long would different forms of travel take to get from one to the other (walking 25 hours, train one hour, Concorde four minutes, rocket 20 seconds)?

Writing

Discuss suitable words and phrases to describe the scene in the picture, and thenwrite an evocative account of it.

Talking points

After the recent terrible air crash in Paris, should Concorde be scrapped?

For

What is the point of travelling faster and faster? You can get to most places nowadays in a few hours, so we should not risk lives to save time. Concorde is an outdated aeroplane, and travelling in it is just a status symbol. Supersonic flight also damages the environment and pollutes the atmosphere.

Against

Concorde’s safety record is excellent. It is a natural human desire to travel faster and we should develop planes to fly to Australia in one hour - which is much better than the three months it used to take by boat. A trip on Concorde is an unforgettable experience for the many ordinary people who save up for one.

Ted Wragg is professor of education at Exeter University.