BBC News made an interesting post about the science of the Olympic running track. The track has to be designed to be comfortable for the athletes to run on as well as giving them the best conditions for top speeds. To achieve this it has been made of two layers. The top layer is designed to maximise the friction between the show and the track, a feature which can be enhanced by spikes added to the shoes. Most people associate friction with being slowed rather than speeding up but without friction we wouldn’t be able to move at all. As the athlete runs, the ball of their foot pushes backwards onto the track. As a result of Newton’s 3rd Law of Motion this causes the track to push forward on the athlete with equal force. The more friction there is between the shoe and the track, the more energy can be transferred into this forward push, rather than the foot slipping backwards.
The lower surface is designed for shock absorption. This not only provides an extra ‘spring’ to the athlete, pushing them forwards, but also helps reduce damage to their joints. When the surface that you are running on is hard, such as concrete, as you hit your feet against the floor with each step there is a high rate of change in momentum which leads to a large force being applied to the joints. By using a ‘springy’ surface the time taken for each impact with the floor is increased, thus reducing the rate of change of momentum and hence the force applied to the joints.