EDU4SBM Sports Biomechanics 1 Lecture Week 4 Principals of Movement, Momentum, Newtons Laws, Levers

EDU4SBM Sports Biomechanics

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Lecture Week 4Lecture Week 4

Principals of Movement, Principals of Movement, Momentum, Newtons Laws, Momentum, Newtons Laws,

LeversLevers


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MomentumMomentum describes the quantity of motion that occurs.

An athletes momentum is dependent on how massive the athlete is and how fast the athlete is travelling.

The runner has a mass of 75 kg and is running at 5 m.s-1.

What momentum does he have ?


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Conservation of Momentum

In a closed system, such as when two objects collide, the total momentum remains the same.

For example, when a baseball bat hits the ball, the ball will be squished to a certain degree. After few milliseconds, it rebounds back.

This contraction and rebound action is causes the release of heat energy, and some momentum is lost, or transferred elsewhere.


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Maximizing Momentum As momentum is the product of mass and the velocity, you can increase

momentum by increase either of these elements.

In sport


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Momentum

Momentum (p) = mv Question: A 100kg footballer travelling at 6.5 m/s collides

head on with a 50kg player travelling at 10m/s in the opposite direction.

a) What is the individual momentum of each player ?

Player 1: p = 100 X 6.5 = 650

Player 2: p = 50 x 10 = 500


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Momentum Momentum (p) = mvQuestion: A 100kg footballer travelling at 6.5 m/s collides head on with a 50kg

player travelling at 10m/s in the opposite direction.

b) What is the combined momentum of the players combined after collision.

As they are travelling in opposite directions:650 500 resultant momentum = 150

c) What is their combined velocity ?

P = 150Combined mass = 150kg


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Impulse

When a force is applied to an object, the product of the force (F) and the length of time (t) that the force is applied, is called the impulse of the force.

Impulse = Ft measured in Newton Seconds.


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Impulse

Depends on:


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Impulse

In a collision, the impulse experienced by an object equals the change in momentum of the object. In equation form:

IMPULSE = F * t = m * change in v

In starting blocks:

M = 60 kg

V = 0

Momentum = _____

Out of blocks after 1 sec:

M = 60kg

V = 6 m/s

Momentum = ______

Impulse = ______

Force = ________


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Impulse (change in momentum)

Impulse = Ft

F = ma therefore Impulse = mat

Eg: If a 90 kg man is applying a force of 60 N to a toboggan for 7 seconds, what is the impulse exerted on the toboggan.

Impulse = Ft=


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The Follow Through in Sport

In racket and bat sports, hitters are often encouraged to follow-through when striking a ball.

Following through increases the time over which a collision occurs therefore increasing the impulse

This contributes to an increase in the velocity change of the ball.

By following through, a hitter can hit the ball in such a way that it leaves the bat or racket with more velocity (i.e., the ball is moving faster). In tennis, baseball, racket ball, etc., giving the ball a high velocity often leads to greater success.


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The Affect of Collision Time upon the Force

An object with 100 units of momentum must experience 100 units of impulse in order to be brought to a stop.

Any combination of force and time could be used .

Force Time Impulse

100 1 100

50 2 100

20 5 100

10 10 100


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Force Reception/ Absorption

In cricket the ball is "cradled" when caught and the cupped hands move away from the oncoming ball.

The effect of this strategy is to lengthen the time over which the collision occurs and so reduce the force on the lacrosse ball.


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Newtons First Law of Motion

"All bodies continue in a state of rest or uniform motion in a straight line unless acted upon by some external force."

For example: A sprinter

The high jumper will not take off from his approach run unless a force is applied to change direction.


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Newton's Second Law of Motion - Law of Acceleration

“The amount of acceleration produced when an unbalanced force acts on a body is proportional to the size of that force

A sprinter's acceleration from the blocks is proportional to the force exerted against the blocks.


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In the throwing events, the larger the force exerted on an implement, the greater will be the acceleration and consequently, distance thrown.


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Force = mass X acceleration

Mass = 2 kg

Accel = 30 m s2

Force =

Force = 20 kg m s2

Accel = 5 m s2

Mass =

Force = 20 kg m s2

Mass = 4 m kg

Accel =


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Newton's Third Law of Motion – Conservation of Momentum

“For every action there is an equal and opposite reaction

A runner exerts a force against the ground. This creates an equal and opposite reaction force which moves the body over the ground.


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EDU4SBM Sports Biomechanics21

Action-reaction pairs are shown in the following diagrams

Draw the direction on the diagram and state the action and reaction in each case

Action ___________Reaction ___________

Action ___________Reaction ___________

Action ___________Reaction ___________


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Collisions and Newton's third law of motion

In a collision between two objects, both objects experience forces which are equal in magnitude and opposite in direction. Such forces often cause one object to speed up (gain momentum) and the other object to slow down (lose momentum).

According to Newton's third law, the forces on the two objects are equal in magnitude.


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Action/Reaction in Golf

Both club head and ball experience equal forces (action/reaction), yet the ball experiences a greater acceleration due to its smaller mass.

In a collision, there is a force on both objects which causes an acceleration of both objects.

The forces are equal in magnitude and opposite in direction, yet the least massive object receives the greatest acceleration.


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Action/Reaction in the Long Jump

The law of reaction also applies to movements that occur in the air. In these situations the equal and opposite reaction is shown in movements of other parts of the body. A long jumper, for example, will bring the arms and trunk forward in preparation for landing.

The equal and opposite reaction is movement of the legs into a good position for landing.


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Newton’s Laws

Law 3: Action reaction

Eg: If a 90kg player collides with an 80 kg player with a force of 450 N, how much force is exerted by the second on the first ?


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Levers

What do levers have to do with human movement?

In biomechanics we are concerned with levers in sports such as bats, clubs or racquets.

In our human body our muscles bones and joints work as levers.


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Types of Levers

Levers are divided into three groups called first, second and third class.

The axis or pivot point is also known as the fulcrum.

A lever comprises of three components -

(A) Axis or Fulcrum - the point about which the lever rotates

(R) Resistance - the force applied by the lever system

(F) Force - the force applied by the user of the lever system

The way in which a lever will operate is dependent on the type of lever.


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Class 1

Class 2

Class 3

Axis (fulcrun)

Axis (fulcrun)

Axis (fulcrun)

Force Arm

Force Arm

Force Arm

Resistance

Resistance

Resistance

FAR

ARF

RFA


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Class 1 Lever

Axis (fulcrun)

Force Arm

Resistance

•When axis is close to force produces speed

•When axis close to resistance produces power

About 25% of muscles in body are first class levers.

Examples: Triceps extension


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Class 2 Lever

Axis (fulcrun)

Force Arm

Resistance

Very few occurrences in body.

Examples:

Standing heel lift


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Class 3 Lever

Axis (fulcrun)

Force Arm

Resistance

Class 3 is the most common class of lever to be found in the human body.

Usually produce speed at the expense of force.

Examples:

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EDU4SBM Sports Biomechanics 1 Lecture Week 4 Principals of Movement, Momentum, Newtons Laws, Levers