biomechanics

Newton’s first law of motion - law of inertia

A body will remain in a state of rest or uniform motion until an external force acts upon it - penalty the ball will remain on the spot unless it is kicked by the player

Newton’s second law of motion - law of inertia

The acceleration is directly proportional to the magnitude of the force produced and is governed by the direction the force is applied - force = mass x acceleration

• a large force on the ball so that it accelerates over the net in the direction in which the force has been applied

Newton’s third law of motion - law of inertia

For every action there is an equal and opposite reaction - when a footballer jumps up to win a header a force is exerted on the ground in order to gain height. At the same time the ground exerts an upward force upon the player

Scalars

• Measurements are only described in terms of magnitude

• speed

• Distance

• Mass

Vector quantities

• Measurements are described in terms of size and direction

• Weight

• Displacement

• Velocity

• Acceleration

• Momentum

Define centre of mass

• the point of balance

Factors affecting stability

• the height of the centre of mass - lowering centre of mass = increase in stability

• Position of the line of gravity - more central = more stable

• Area of the support base - the more contact points, the larger the base of support becomes and the more stability increases

• Mass of the performer - greater mass = more stability due to increased inertia

• Size of base

• Friction

Example of centre of mass

• a low stance in rugby makes it harder for an opponent to push you over

3 components of levers

• fulcrum

• Load

• Effort

Acronym for levers

• E F L

• F L E

• F E L

Mechanical advantage

• effort arm is longer than the load arm

• 2nd class

• Slow

• Limited range of movement

• Lift heavy loads easily

Mechanical disadvantage

• where the resistance arm is longer than the effort arm

• 1st and 3rd class

• Large range of movement

• Resistance can be moved quickly

• Cannot apply much to move an object

First class lever

• Load arm longer than effort arm

• movement of head, neck and elbow extension - eg press up or throw

• Flexion and extension

• Mechanical disadvantage

Second class lever

• effort arm longer than load arm

• Plantar flexion of the ankle eg jumping or running

• Mechanical advantage

• 2nd class

Third class lever

• load arm longer than effort arm

• Everything else eg bicep curl or kicking

• Hip, knee and elbow flexion

• Mechanical disadvantage

Definitely mass

• quantity of matter the body possesses

• Kg

• Scalar

Define weight

• force exerted on the mass of the body by gravity

• Newtons

• Vector

Define distance

• the path a body takes as it moves from the starting to the finishing postion

• Metres

• Scalar

Define displacement

• shortest route in a straight line between the starting and finishing postion

• Vector

Define speed

• the Body’s movement per unit of time

• Seconds

• Scalar

Define velocity

• the rate change of displacement

• Seconds

• Vector

Define acceleration

• the rate of change of velocity

• M/s2

• Vector

Define momentum

• amount of motion a body possesses, product of mass + velocity

• K/g/m/s

• Vector

Forces acting upon a performer during linear motion - vertical forces

• weight - the gravitational force exerted on an object

• Ground reaction force - two bodies are in contact with one another- the force acting on a performer during linear motion, a reaction force will be generated - newton 3rd law

Forces acting upon a performer during linear motion - horizontal forces

• frictional force - occurs when two or more bodies are in contact with one another - is opposite to the direction of any potential slipping

• Air resistance - force that acts in the opposite direction to the motion of a body travelling through air

Define impulse

• impulse = force x time

• Time it takes a force to be applied to an object or body

Using impulse to increase momentum

• increasing the amount of muscular force that is applied eg basketball - a large force is genarte when jumping for a rebound in order to get as much height as possible

• Increasing the amount of time in which a force is applied

Using impulse to decrease momentum

• increasing the time forces act upon them - eg gymnast dismounting from the parallel bars, flexion of the hip, knee and ankle occurs which extends the time of the force on the ground which allows the gymnast to control the landing and reduce the risk of injury

Angular motion

Movement around a fixed point or axis - occurs when a force is applied outside the centre of mass

Torque

• the rotational consequences of a force

• It causes an object to turn about its axis of rotation

• Torque = force x perpendicular distance from the fulcrum

Ways to increase torque

• increasing the size of the force

• Applying the same force further away from the axis of rotation

• The perpendicular distance of the force from the pivotal point

Newton’s first law - angular motion

A rotating body will continue to turn about its axis of rotation with constant angular momentum unless an external rotational force is extend upon it

Example of Newton’s first law - angular motion

An ice skater spinning in the air - continue to spin until they land on the ice when an external force is exerted from the ice on their skates which changes their state of angular momentum

Newtons 2nd law - angular motion

The rate of change of Angular momentum of a body is proportional to the force causing it and the change that takes place in the direction in which the force acts

• the greater the torque entered the faster the rotation will be

Newtons 3rd law - angular motion

When a force is applied by one body to another the second body will exert an equal and opposite force on the other body

Example of Newtons 3rd law - angular motion

Goalkeeper tips the ball over the bar they throw their arms up which causes the lower part of their legs to go back

Define angular displacement

The smallest change in angle between the start and finish point of a rotation

Define angular velocity

The rate of change of angular displacement

• AV = AD divided by time taken

Define angular acceleration

The rate of change of angular velocity

• angular acceleration = change in angular velocity divided by time taken

Define moment of inertia

• Resistance of a body to angular motion

• This can be applied to the start of rotation where a body will resist angular motion but once the rotation occurs the body will want to continue to turn about its axis of rotation

Two factors that moment of inertia depend upon

• mass of the body

• The distribution of mass around the axis

Moment of inertia - mass of the body

The greater the mass the greater the resistance to change and therefore the greater the moment of inertia

Moment of inertia - the distribution of mass from the axis of rotation

• The closer the mass is to the axis of rotation the easier it is to turn because the moment of inertia is low

• Increasing the distance of the distribution of mass will increase the moment of inertia

• Example - somersault in an open position has a higher moment of inertia than a tucked somersault because in the straight position the distribution of the drivers mass is further from their axis

Define angular momentum

The quantity of rotation a body possesses

• AM = MOI X AV

• If moment of inertia increase angular velocity decreases

Angular momentum

• angular momentum is a conserved quantity - it says constant unless an external torque acts upon it (newtons first law)

• A performer an alter the speed of rotation by changing their body position to increase or decrease their moment of inertia

Example of angular momentum - diver And ice skater

• when diver performs a double somersault from the 10m board, the amount of angular momentum stays the same during flight and only changes when the diver hits the water on entry or changes their body position

• Ice is friction free surface so there is no resistance - at the start of the spin the arms and legs are stretched out. This increases their distance from the axis of rotation resulting in a large moment of inertia and a large angular momentum in order to start the spin so rotation is slow - when they bring their arms and legs back in line with the rets of the body the distance of these body parts to the axis of rotation decreases. This reduces the moment of inertia which in turn increases their angular velocity and the skater spins quickly

3 factors affecting the horizontal displacement of a projectile

• angle of release

• Speed of release

• Height of release

Angle of release

• the optimum angle of release is dependent upon release height and landing height - when release height and landing height are equal then optimum angle of release is 45

• If the release height is below the landing then the optimum angle of release needs to be greater than 45 - shooting in basketball

• If release height is greater than landing height the optimum angle of release needs to be less than 45 eg. Shot put - release angle smaller means more speed can be generated

Speed of release

The greater the release velocity of a projectile the greater the horizontal displacement travelled

Height of release

The greater the release height results in an increase in horizontal displacement

Factors affecting flight paths of different projectiles

• weight and air resistance

• Projectiles with a large weight force have a small air resistance force and follow a parabolic flight path eg shot put

Define parabola and example

A curve with matching left and right hand sides eg. Shot put

Non parabolic flight path example

Badminton shuttlecock - lighter mass and an usual shape that increases its air resistance

Define drag force

A force that acts in opposition to motion - slows something down

Two types of drag

• surface drag - friction between the surface of an object and the fluid environment - swimmers wear specialised clothing to reduce surface drag

• Form drag - impact of the fluid environment on an object - forces affecting the leading edge of an object increase form drag and the orcas affecting the trailing edge reduce form drags eg. A cyclist will use another riders slipstream as wind hits the front cyclist it goes around the sides and cyclist behind uses the air pocket that has been created

Factors that increase drag

• the velocity of the moving body - the greater the velocity of a body through a fluid the greater the drag force eg. Racer ,cyclists will experience greater air resistance in their competition which increases drag

• The cross sectional area of a moving body - a large cross sectional area increases drag eg. Sitting upright in cycling

• The shape and surface characteristics of a moving body - uneven shapes create more turbulence behind them increases drag and rough surfaces increase friction therefore increasing drag eg. Dimples on a golf ball reduce turbulent separation and can reduce overall drag, allowing the ball to travel farther. Or Loose clothing flaps and disturbs airflow → more drag. or shuttlecock has unusual shape with feathers and it is very light - the larger drag force from air resistance mean it loses speed

Factors that reduce drag

• the velocity of a moving body - streamlining the body as much as possible - which means shaping a body. So it can move as effectively and quilt through a fluid as possible

• The cross sectional area of the moving body - reducing the effects of drag eg. In the Tour de France the competitors reduce their cross sectional area by crouching low over the handlebars

• The shape and surface characteristics of a moving body - more streamlined, aerodynamic shape reduces drag. Eg. The speed skier has a helmet that extends to their shoulders to give them a more streamlined position and aerodynamic boots. Elite swimmers shave off all body hair and wear half body swimsuits so they create a smooth surface and swimming caps