The Physics of Sprinting Experiment-The Best Start
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Investigating the Sprint Start

Now that you know about the three types of sprint starts, you're probably wondering, "Which one is the best?" We will now show and explain to you which one is the most effective in giving you the best possible time.

We made an experiment to test the different sprint starts so that you can learn about the types of starts and figure out which one is the best on your own. If you chose to complete the experiment, you can check with our results later.

First of all, you have to know what you are trying to achieve when deciding which start is the most effective. The purpose of the start is to give you the best possible acceleration out of the starting position as well as giving you the best velocity and reaction time out of the blocks.

Now, here is our experiment which we devised to find which start is the most effective in giving you the best velocity. In order to have a good velocity, you need to have a good IMPULSE off of the blocks. Impulse is the force acting over a period of time. In this case, it would be the force your feet pushes against the block over the time at the beginning of the race to allow you to accelerate to the fastest initial velocity.

SPRINT START EXPERIMENT

PURPOSE:

To study the three different crouched starts and to determine which is the most effective in achieving the greatest impulse giving the sprinter the best velocity out of the starting position.

MATERIALS:

-stopwatch

-measuring tape

-running track

THEORY:

We have to use two different formulae in this experiment. Here is an explanation of them.

v=d/t

This is the formula for velocity. Velocity is the same as speed. The only difference is that velocity has direction, where speed doesn't. Velocity is the quotient of the sprinters displacement (distance covered) and the time it takes to travel this distance.

(F)(t)=(m)(v)f-(m)(v)i

This is the impulse momentum formula. You're probably wondering what its all about, but when its broken down it can be very simple.

first of all:

Impulse is equal to the force acted over time (as already mentioned). It is shown like this:

impulse=(F)(t)

Since we can not determine the force very easily, we are going to use another approach. Impulse is also equal to the chage in MOMENTUM. Momentum is the product of the object's. or in this case the sprinter's, mass and velocity. Momentum is used a lot everyday in describing different things, such as saying "The player is gathering momentum as he moves down the ice" or "The cars momentum carried it off the road." Momentum is difficult to explain but hopefully you'll get the general idea.

Because it is easier to determine the runner's mass and velocity, we will be using this formula, the change in momentum, to determine impulse.

PROCEDURE

1)First of all, find a smooth flat running surface.

2)Then measure out a distance of 10 m from the starting line.

3)Then have the runner get into the bunched start at the starting line. The buched, or bullet start, is the start which your front foot and back foot are closest together in the starting position.(there are pictures at the bottom to give a visual explanation)

4)Then have another person at the finish line (10 metres away) to time the runner's first portion of the race.

5)Then have the runner in the bunched start practice sprinting to the 10 metre line at least three times to insure that they are able to perform it.

6)Then time the person, using this start, three times.

7)Then move on to the medium start. This is the start where your feet aren't close together, but they aren't far apart either. The toe to toe distance is opproxomately 40-55cm's.

(there are pictures of this at the bottom)

8)Have this one practiced then record the times of three trials.

9)Then repeat the same experiment for the elongated start. The elongated start is the one in which your back foot is furthest behind the front one.

10)After the times for the nine trials have all been recorded, find the average time it takes to run the 10 metres for each start. (It is easiest to record this information in a chart, we have one you can copy in the results section)

11)Then determine what the velocity was for each of the starts using the velocity formuala: v=d/t

Fill in the distance(10 metres) and the average times for each start to determine the velocity.

12)After, determining the velocity for each start, you can determine the change in momentum. To do this, have to find the momentum before and after. You also must find the mass (in kilograms) of the person running.

To find the initial and final momentum, fill in the velocity and mass for each of the starts into the following formula.

(m)(v)f-(m)(v)i= change in momentum

m=mass v=velocity f=final i=initial

13)Once the change in momentum for each of the sprint starts is calculated, you have the impulse. (this is because the change in momentum is equal to the momentum)

14)Then determine which start gives the greatest impulse. Then you will know which start allows for the greatest force over time resulting in the best velocity out of the blocks.

RESULTS

For our experiment, we tested three different people so that our results would be more accurate.

Speed of Person #1 (mass=42 kg) for 10 m

 Type of Start Trial 1 Trial 2 Trial 3 Average BULLET 3.00 s 3.1 s 2.77 s 2.96 s MEDIUM 2.71 s 2.42 s 2.64 s 2.59 s ElONGATED 3.05 s 2.83 s 2.98 s 2.95 s

Speed of person #2 (mass=57 kg) in 10 m

 Type of Start Trial 1 Trial 2 Trial 3 Average BULLET 3.07 s 2.89 s 2.93 s 2.96 s MEDIUM 2.77 s 2.38 s 2.55 s 2.57 s ELONGATED 3.01 s 2.78 s 2.86 s 2.88 s

Speed of person #3 (mass=60kg) in 10 m

 Type of Start Trial 1 Trial 2 Trial 3 Average BULLET 2.67 s 2.70 s 2.79 s 2.72 s MEDIUM 2.56 s 2.37 s 2.30 s 2.41 s ELONGATED 2.81 s 2.83 s 2.94 s 2.86 s

Velocity of each runner in 10 m

 Person # Velocity of Bullet Start Velocity of Medium Start Velocity of Elongated Start #1 3.38 m/s 3.86 m/s 3.39 m/s # 2 3.38 m/s 3.89 m/s 3.47 m/s # 4 3.68 m/s 4.15 m/s 3.50 m/s

Momentum of each person in each start for 10 m

 Person # Momentum of Bullet start Momentum of Medium start Momentum of Elongated start #1 141.96 kg * m/s 162.12 kg *m/s 142.38 kg *m/s #2 192.66 kg  * m/s 221.73 kg *m/s 197.79 kg *m/s #3 220.8  kg * m/s 249.00 kg *m/s 210.00 kg *m/s

DISCUSSION OF RESULTS

According to the results of our experiments, the medium start produces the greatest change in momentum. Because change in momentum is equal to impulse, the medium start has the greatest impulse (force acting over time). The greater the impulse of the start, the faster the velocity will be. Because the medium start has the greatest impulse, it will produce the fastest possible velocity out of the blocks.

COMPARING THE STARTS

In the bullet start the sprinter is only in contact with the blocks for a short time , unabling them to produce a good force in this time. Which also means that they do not have a good impulse. Therefore, the sprinter will not be able to achieve the best possible velocity.

With the elongated start the sprinter has contact with the blocks over a greater time but because of the position they are in they can not produce a good force on the blocks. The feet are too far apart which affects the balance of the runner. They are unable to push of the blocks well enough to produce the best possible velocity.

When starting in the medium position the sprinter is in a good position to exert a good force on the blocks and the runner has more time than the bullet start to push off the blocks.

CONCLUSION

The MEDIUM START is the start that allows sprinters to produce the greatest impulse allowing then to get the greatest possible velocity when leaving the blocks.

 Example of a Bullet start

 Example of a Medium start

 Example of an Elongated start