Scienceville
Moving on Tracks
Why don't trains slide off the rails on a curve? Why are there stones under the tracks? Let's discover the clever science that keeps trains rolling safely.
Did you know?
Train wheels are not flat like the edge of a coin. Each wheel is slightly cone-shaped. On a curve, the outer wheel rolls on its wider part, covers more ground and helps steer the train round the bend.
The stones under railway tracks are called ballast. They hold the sleepers (the concrete or wooden beams under the rails) in place, carry the weight of trains and let rainwater drain away. Their sharp edges lock together.
The Gotthard Base Tunnel in Switzerland, opened in 2016, is the world's longest and deepest railway tunnel. It is about 57 km long, and at one point about 2,450 metres of mountain rock rises above it!
Try this: Roll a Train Wheel
Do this with an adult
With an adult, tape two paper cups together at their wide rims. Lay two rulers side by side, a little apart, and rest one end on a book to make a sloping track. Roll the cups down the rulers: they stay on! Now tape two cups together at their narrow bottoms and try again. What happens? Real train wheels are shaped like the first pair.
Go further: Why Rails Went Clickety-Clack
Steel grows a tiny bit longer when it gets hot. On older railway tracks, small gaps were left between the rails, so that they had room to stretch in summer. Wheels bumping over these gaps made the famous 'clickety-clack' sound! Today, many tracks use long welded rails with hardly any gaps. They are fastened firmly to the sleepers and held by the ballast, which helps keep them in line even on hot days.