Running skills

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Newtons laws of motion

Newtons 1st law:

On the starting blocks, sprinter will remain at rest until an external force is applies/acts. The upward and forward reaction force from the blocks

Newtons 2nd law:

Greater force applied by the sprinter on the blocks and during first few struides the greater the sprinters acceleration at the start of the race

Newtons 3rd law:

When the sprinter pushes backwards on the track with their legs the track exerts an equal and opposite forward force on the athlete.

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Graph of motion

(http://www.bbc.co.uk/schools/gcsebitesize/science/images/add_ocr_velocitytime.gif)

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Net Force and Stability

Net Force :

During acceleration phase net force is +ve as horizontal forces are unbalanced. When sprinter has achieved max speed and is at constant velocity the net force is 0. When sprinter is decelerating slightly at end of race net force is -ve as horizontal forces are unbalanced.

Stability:

' On your marks' = most stable due to low CoM, area of base of support is large and line of gravity is central to the base of support

'Set' = still stable but less stable as CoM is higher and the line of gravity is closer to the edge of the base of support.

'Bang' = sprinter unstable as lifting hands off the ground means that the line of gravity falls outside the base of support and CoM is higher.

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Free body diagram

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Lever systems

2nd Class:

Used in the ball of the foot, phalanges/metatarsals

F= joint between the metatarsals and phalanges

L= weight of the body being moved

E= force exerted by the gastrocnemius muscle as it contracts to cause plantar flexion of the ankle.

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Lever systems (continued)

3rd Class:

There are a number of 3rd class lever systems however eg will be of the hip.

F= hip joint

L= weight of the leg

E= force exerted by the iliopsoas muscle as it contracts to cause flexion of the hip

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Impulse

Impulse = Force x time

During acceleration phase the +ve impulse > -ve impulse resulting in a +ve net force in the direction of travel

During the deceleration phase the -ve impulse > +ve impulse resulting in a -ve net force in the direction of travel

At max speed -ve impulse = +ve impulse resulting in a net force of 0

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Moment of Inertia

To increase moment of inertia the distribution of the mass of the body needs to be further from the axis of rotation therefore less spins/sumersaults can be performed as rotatkion is slower

To decrease moment of inertia the distribution of the mass of the body needs to be closer to the axis of rotation. This causes the roation to be faster.

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