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Oscar Pretorius is known as the fastest man with no legs. He is in fact a runner with a difference: he was born without bones in his lower legs. Before he was just one years old doctors amputated his legs below the knee as they would never have been strong enough to hold him up.

Oscar was determined not to be beaten. At the age of 21 he had already won a gold medal in the 200 metres and a bronze medal in the 100 metres at the 2004 Paralympic Games in Athens, Greece. Now, Oscar wants to complete in the Olympic Games alongside able-bodied athletes.

Oscar Pretorius

Oscar has been nicknamed ‘The Blade Runner’ because he uses a pair of artificial legs which look like springy blades. The blades are made from carbon fibre and are called Cheetahs.

Oscar can run very fast with the cheetahs on. He has run 400 metres in 46.56 seconds. The world record for an able-bodied athlete at 400 metres is 43.18 seconds. So Oscar's record is only 3.38 seconds slower than an athlete using his or her own legs. At that speed, he would stand a very good chance of qualifying for Olympic competition.

Is there a problem with the cheetahs?

Some people say that the artificial legs give Oscar an 'unfair advantage' over able-bodied athletes. They argue that he can run faster than anyone else using the blades.

There are two ways the blades could give Oscar an unfair advantage:

By adding height?

If the blades make Oscar taller than he would have been with his own legs, his stride would be longer. A longer stride could help him run faster.

Is it possible to work out how tall Oscar would have been?

Yes, scientists can work out how tall Oscar would have been if he had his own legs. Our upper and lower legs tend to be in proportion, this means that your upper leg is the same length as your lower leg. By measuring Oscar’s upper legs, scientists can work out how tall Oscar would 'probably' have been. Forensic scientists use the same method to work out how tall murder victims would have been when parts of the skeleton is missing. Scientists use this method to help them identify people.

By storing more energy?

If the blades store more energy compared to human legs, this could help Oscar run much faster.

To give us a good idea about how well the blades store energy we can look to nature. Kangaroos can hop for miles and at great speed because they have really elastic tendons in their hind legs that store lots of energy.

How can the cheetahs store more energy?

It’s just like bouncing balls!

Everytime a ball hits the ground some of its kinetic energy is stored as elastic potential energy. When the ball bounces up, the elastic potential energy is converted back into kinetic energy. The more energy it stores, the higher it bounces.

A squash ball does not store much energy so it hardly bounces. Because it doesn't store much energy, the squash player has to put more energy into the ball to hit the wall. This is why squash is a very energetic game. Tennis balls store much more energy and so bounce much better.

Elastic potential energy stored in different games

Kangaroos store a lot of energy in their hind legs. They can reach speeds of 50Km/h (about 80 miles per hour) and can keep it up for hours at a time. In contrast, top human athletes reach a top speed of about 35Km per hour (about 22 miles per hour) and can keep it up for only a few seconds.

Kangaroo's

As for Oscar, he did not compete at the Beijing Olympics. The International Association of Athletics Federations (IAAF) decided that his blades store too much energy and therefore give him an unfair advantage over able-bodied athletes.

The big questions:

What should an athlete look like?

Should technology be allowed to help athletes compete?

Would sport be changed if athletes using artificial limbs could run faster or jump higher than the best athletes using their own natural limbs?

Why do you think bipedal bouncy creatures only evolved in Australia?

Project:

Make a jumping device!

It must store potential energy and lift itself and all its contents (no water rockets!) to the greatest possible height. Remember you can store elastic potential energy in springs, rubber bands, compressed air etc.

If you come up with a good design send us some pictures, video or stills, and the height achieved and we will showcase the best designs.