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# The physics behind track

Science unit project
by

## Haley Webb

on 22 February 2013

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#### Transcript of The physics behind track

Going The Distance: By: Haley Webb The world's fastest man uses a lot of force
when he runs. Usain Bolt needs to use more force than his competitors when he runs. That's because he is 6'5" and weighs around 207 pounds. A man like him is not expected to be the fastest person in the world. That's because he needs a lot of force to propel him forward. Force Newton's second law applies to two field events in track. Those events are shot put and discus. The shot put ball weighs more than the discus. Since the shot (shot put ball) weighs more than the discus, it would need to be thrown with a greater force to reach the same acceleration as the discus. Here's an example... Newtons Second Law Have you ever noticed that runners don't stop immediately once they stop the finish line? Well, that's because as a runner is sprinting, they are accelerating and building up momentum. Once someone reaches a fast speed they are hard to stop, or it's hard to change their speed. That's inertia, or Newton's first law, acting upon them (the tendency to resist change).
Newton's first law applies at the starting line too. Sprinters use starting blocks to help them have a quicker starting time. While they are on the blocks (on the starting line) they are completely motionless. Then once the gun shoots off, the sprinters immediately kick off the starting blocks and are in motion. The sprinters were at rest, then (once they started) they were in motion. The object at rest was the sprinters, the outside force was the sprinters kicking off the blocks, and then the sprinters were in motion. Newtons First Law A runner builds potential before a race. As they position themselves on the blocks, they are building up potential energy. Let's take the 100m dash for example. As a runner is on the starting blocks they are building up potential energy because they aren't in motion and they have the potential to move. The energy that they are building up has the potential to be changed into another form of energy. In this case the potential energy will changed into kinetic energy. The potential energy is changed to kinetic energy when the runner starts the dash. Kinetic energy is the energy someone/something has while they're in motion. So, as someone is running the 100m dash they are using kinetic energy. Potential and Kinetic Energy When Usain Bolt runs, he puts a lot of
force into the ground. With each step
he takes, he generates a huge amount
of force against the ground. The ground
produces that same amount of force,
and applies it back to propel Bolt forward.
He needs more force to propel him
forward because he weighs more, and he is
taller than his competitors. The more you
weigh (the more mass you have) the more force is needed to propel you forward (according to Newton's second law).
That's not a problem for Bolt because
he has a lot of muscle, especially arm
muscle. While running, arm muscles
produce one third of your speed. Luckily, Bolt works just as hard in the weight room as he does on the track, and he has quite a bit of arm
muscle. His arm muscles help propel him
forward and allow him top speed and force
while running. Say that a shot weighs 10 kg and a discus weighs 5 kg. If both were thrown with a force of 20N the discus would have a greater acceleration. In fact, the discus' acceleration would be twice the acceleration of the shot. The discus would accelerate at 4m/s squared while the shot would accelerate at 2m/s squared. As you can see, you need to throw something with a big mass with more force to reach the same acceleration of an object with less mass. Newton's Third Law of Motion Let's go back to the starting blocks. Newton's third law of motion applies here too. Newton's third law states that for every action there is an equal and opposite reaction. Well, that is the whole case with the starting blocks. A runner is motionless on the blocks. When they kick off the blocks that is the action. Whenever they kick off the blocks, the blocks move backwards. That is the equal and opposite reaction. The Physics Behind Track and Field
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