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Set up an investigation into road surfaces. It is vital that the surface allows good grip for the tyres of vehicles. Too smooth and slippery and the car or lorry cannot stop (or even start) safely. However, it must not be too rough and bumpy, or else it would be uncomfortably bouncy. Use a model car, a shoe or a trainer, weighed down with something. Use a Newton-meter (or hook some rubber bands and measure their stretch) to pull it along a surface. Measure the forces to start it moving and also to keep it moving.

When you stop pulling, how far does it travel before it comes to a stop? Now change the surface, using the floor and the table, maybe the grass outside or part of a garden, or tarmac. You can even make up some surfaces in a tray ( marbles, soil, gravel, sand, possibly water or ice). Compare the results for different surfaces, and discuss ideas of friction and, thus, why the road surface texture is crucial. The careful use of some oil on a tray might show how dangerously slippery a road becomes when oil leaks onto it. Students can look into the structure of roads and the history and nature of tarmac, right up to date with issues of braking distances on some newer road coatings.

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