# Jumping skills

## Newtons laws of motion

Newtons 1st law:

The jumper will remain running at optimal speed on the approach run until acted upon by an external force at take off. Once the jumper plants a foot on the takeoff board the board applies an upward force on the jumpers foot, changing their state of motion.

Newtons 2nd law:

The greater the reaction force generated at takeoff the greater the upward acceleration achieved

Newtons 3rd law:

At point of takeoff, the jumper exerts a downwards force on the ground and the ground exerts an equal and opposite reaction force on the jumper allowing the jumper to accelerate upwards at takeoff.

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## Net force and Free body diagragm

Net force acting on a long jumper during approach run is +ve as they accelerate from a stationary position at the start of their run to reaching their optimal speed at the moment of takeoff

Horizontal forces are unbalanced, F>AR. A long jumper can maximise friction by wearing spikes and minimising their air resistance by wearing tight fitting lycra. Will also start their run approach with a slightly crouched position and gradually become more upright to reduce their cross sectional area.

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## Impulse

Penultimate stride, long jumper will lean backwards slightly and dip into the ground lowering their CoM, allowing their foot to stay in contact with the ground for longer which means that there is greater time for which the force is applied.

Impulse = force x time

Therefore applying to Newtons 2nd law means that a greater impulse will result in an increase in the rate of change of momentum and increase the velocity with which the jumper leaves the ground. Therefore gives the jumper a greater upward acceleration and height at takeoff

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## Projectiles and CoM

During flight only weight and air resistance acts on the performer. AR is negligible for this small amount of time and therefore the CoM follows a path that is very close to a true parabola.

CoM:

at takeoff, reaction force passes behind the jumpers CoM which is an eccentric force that generates angular motion. Therfore during flight there is a tendency to rotate forwards. In order to conteract this rotation the long jumper uses the hang or the hitchkcik.

During flight just before the landing the arms and legs are stretched out in front therefore their CoM moves forwards and lies outside the body. This is beneficial as it minimises the risk of falling backwards into the pit on landing.

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## Lever systems

The performer uses all 3 lever systems.

2nd class lever system:

= mechanical advantage as it allows a heavy load to be moved with little effort over short distances. It is in the metatarsals and phalanges joint in the foot

F= joint between the metatarsals and the tphalanges

L= weight of the body

E= contraction of the gastrocnemius to cause plantar flexion of the foot.

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