Biomechanics

Question 1

Moment of Inertia (MOI)

Answer 1

is a body’s resistance to a change in its state of angular/rotational force. It is the difficulty to change an object’s rotational motion. Moment of Inertia is equal to the mass of the object multiplied by the radius of rotation (moment).
MOI=mass of the object x radius of rotation

Question 2

conservation of angular momentum

Answer 2

a spinning body will continue spinning indefinitely unless an external force acts on it.

Question 3

Angular momentum

Answer 3

is the rotational or angular motion possessed by an object.Angular momentum of the body / object remains constant unless external forces act upon it

Question 4

To increase angualr momentum prior to take off athletes can..

Answer 4

Increase linear momentum (run up speed) which is then transferred into angular momentum
Improve segmental interaction at take off

Question 5

fulcrum/axis

Answer 5

point around which the lever rotates

Question 6

Effort/force arm

Answer 6

the distance between the fulcrum and the point at
which the force is applied.

Question 7

Resistance arm

Answer 7

the distance between the fulcrum and the
centre of the resistance

Question 8

Input (Effort) Force

Answer 8

Force exerted ON the lever

Question 9

Output (Resistance) Force

Answer 9

Force exerted BY the lever

Question 10

First Class leaver

Answer 10

F | R
Axis in Middle
e.g Tricep Extension

Question 11

Second Class

Answer 11

|R F
Resistance in middle
E.g

R F

Question 12

Third Class

Answer 12

3rd class levers, where the axis/fulcrum is located at one end with application of the force in the middle and resistance applied at the opposite end is the most common type of lever in the human body.

| F

F R

Question 13

factors effecting levers

Answer 13

Length of the lever
Velocity is greatest at the distal end of a lever
Longer the lever, greater the velocity at impact E.g. Golf driver vs. 9 iron
↑ club length creates ↑ velocity and momentum at impact provided the athlete can control the longer lever – longer generally means↑ mass!
Children often have difficulty with this and subsequently use shorter levers to gain better control – shorter cricket bat, tennis racquet etc

The inertia of the lever
The longer the lever, the heavier it usually is and therefore the more difficult it is to rotate
By ‘gripping’ down the club in striking sports, athletes can reduce the rotational inertia of the implement therefore making it easier to swing eg. In ‘bunting’ the ball in softball / baseball

The amount of force
The amount of force an athlete is able to generate via their muscles determines the length of the lever the athlete should use
Longer levers are usually heavier therefore more force is required to move them
As a result, its crucial athletes do not try to use longer, heavier equipment if they are not physically strong enough, as this will sacrifice control!

Question 14

Newtons 1st Law of Motion (inertia)

Answer 14

states that an object will remain at rest unless acted on by an external force. The object will move in the direction of the force acted upon the object. In Soccer, the ball will remain at rest or stationary unless a player strikes the ball. The ball will move in the direction in which the force is acted upon by the player.

Question 15

Inertia

Answer 15

is an object resistance to change its current state or position. An objects inertia is proportional to its mass (weight). The heavier an object/athlete the greater the inertia.

Question 16

newtons 3rd Law of Motion

Answer 16

states for every action there will be an equal and opposite action. If an athlete directs a force with their foot towards the ground, then there will be a ground reaction force of equal force magnitude directed back in the direction towards athlete’s foot.

When two objects exert a force upon each other, the forces are opposite in direction and equal in magnitude.

Question 17

Newtons 2nd Law of motion

Answer 17

states that an objects acceleration is directly proportional to the force acting upon it and is indirectly proportional to its mass. The greater the force applied to the object the greater the acceleration. Alternately, if the mass of the object is reduced, less force is required to attain similar acceleration. The acceleration will act in the same direction of the force and will be conserved until / unless another force acts upon it.
force=mass x acceleration

Question 18

Force Motion (newtons 2nd law)

Answer 18

relates to the magnitude of the force and the direction of the force applied
Magnitude of force - the more force applied the greater acceleration of the ball/object equates to Newton’s 2nd Law (F = MxA)
Athlete pushing/striking/kicking/applying maximum effort will effectively maximise the magnitude of the force applied
Direction of force applied – pushing/striking/kicking/applying the force in the direction of target to increase transfer of momentum through the ball / object.

Question 19

Impulse-momentum (Force-Time Relationship)

Answer 19

force x time. It often can be related to Newton’s Second Law of Motion or the Law of acceleration where the acceleration of the object is proportional to the force applied. Impulse is the change in momentum.

Question 20

Coefficient of Restitution (COR)

Answer 20

Measures the elasticity of the collision between an object and given surface. Measure of how much rebound exists following a collision. The COR determines the measure of momentum that is conserved. If momentum is perfectly conserved the COR is perfectly elastic (or 1.0), if momentum is not conserved then COR is imperfect (or less than 1.0), if the object/ball will not bounce at all, the COR will be zero.

Question 21

Coefficient of Restitution is affected by 3 factors

Answer 21

The materials of the interacting surface. For example, that new tennis balls will have a higher COR than old tennis balls and depending on the surface (ie. grass, clay, hard court) and influence the bounce.
Velocity of the collision. The higher the velocity of the collision will reduce the COR because of the greater compression of the ball. That ‘energy’ being lost as the ball changes its original shape.
Temperature of the materials. As the temperature the ball increases so does the COR. The colder the ball the lower the COR. Tennis, golf and squash are good examples

Question 22

Torque

Answer 22

A force that produces a rotational movement around an axis point (angular motion) from an eccentric force (rotational ‘off-centre’ force).
Torque is calculated by the force multiplied by the perpendicular distance of the moment arm.

Question 23

How can torque be increased

Answer 23

Torque can be increased through the increased application of force generated by the muscular contraction of the athlete.
Alternatively, the athlete could lengthen the perpendicular length of the lever (moment arm) by ensuring their arms are fully extended

Question 24

Segmental Interaction

Answer 24

Is the transfer of energy/momentum between body parts. It is the way the body segments and interacts to meet the demands of the task.
1. Body parts move in a sequence to generate the largest force or acceleration possible.
2. Movement starts with the largest, strongest and slowest segments, working through to the smallest and fastest, resulting in summation of momentum.
3. The next segment begins to move as the preceding segment has reached maximum velocity.
4. The body needs to be well balanced/sequentially stabilised to aid the transfer of momentum across body segments.
5. Follow through is important to prevent deceleration of last segment and safe dissipation of force.
6. All forces are directed to the target.

Question 25

Coordination Continuum

Answer 25

The Coordination Continuum is the sequencing approach to develop motion. By coordinating the segments and transferring angular velocity at its maximum peak to the next moving segment an athlete can generate maximal force production. Effective timing of segments sequentially, avoiding deceleration will maximise force production.

Question 26

Balance (find def)

Answer 26

ability of something to maintain or hold its position.
Widens base of support by standing with feet outside shoulder width (feet spread apart)
Increase surface area to the ground (point of contact) by standing flat footed
Lowers her centre of gravity by bending/crouching
Maintains her line of gravity in the middle of the base of support by marking on photo/puts butt out puts head in the middle

Question 27

range of motion

Answer 27

The degree at which a body segment moves around a joint while in motion.
By extending in arm in the preparation phase / swinging through a greater range of motion, the higher the force that is created during the throw / swing and transferred to the ball, the more momentum it will have and therefore travel with a higher velocity / further.

Question 28

Optimal Projection

Answer 28

Height of release
The position above the ground (or height) at which she releases the ball. The height of release will influence the angle required for a successful shot (or appropriate explanation)

Projection angle
The angle the athlete throws/shoots or releases the ball. The athlete must select an angle that is great enough to allow the ball to go above the player ‘setter’ and come down to a front court position for the ‘set’ (or appropriate explanation)

Velocity or release
The velocity at which the athlete releases the ball. The velocity of release will influence the trajectory of the ball, too fast and the ball goes over the net, too slow the ball drops short (or appropriate explanation)

Question 29

turbulent flow

Answer 29

Flow in which the velocity at any point varies erratically. SEPERATES LATE- less pressure

Question 30

Laminar flow

Answer 30

A type of fluid flow in which fluid moves smoothly in individual layers or streams. SEPERATES EARLY- more pressure

Question 31

form (pressure) drag

Answer 31

Form drag is the resistance created by the pressure differential between the front and the back of an object moving through a fluid (air/water).

Question 32

Boundary separation layer

Answer 32

The layer of fluid immediately adjacent to the body / object creates adhesion between the fluid particles and the body / object surface which creates viscous stress.
The point at which the boundary layer of fluid passing over the body / object separates from the surface is known as the boundary layer separation point.
The different “roughness” on either side of an object (such as a cricket ball) creates different amount of drag on each side of the ball, so the bowler can use this to produce movement of the ball from one side or the other (due to the pressure differentials on either side of the ball).

Question 33

Surface (Skin Friction) Drag

Answer 33

1.Surface drag is the friction between the fluid (air/water) and the surface of a moving object. 2.Smooth, tightly fitting material will assist to decrease drag.
Wearing swimming caps, tight suits, athletes ‘shaving down’, helmets will reduce surface drag.

Question 34

Wave Drag

Answer 34

1. Wave drag is the resistance formed by the creation of waves at the point where air and water interact.
2. This drag comes from the creation of waves as an object (swimmer/boat/craft) moves through the water.

Improving buoyancy (eg. wearing a wetsuit), making the body/object more ‘streamlined’ and improving the technique of the swimmer (eg. increased kicking to enhance buoyancy) / boating craft will decrease wave drag.

Question 35

Bernoulli’s Principle

Answer 35

The velocity of the fluid flow determines the pressure system

Pressure on one side of an object is inversely proportional to the velocity on the same side of the object. As the velocity of the fluid increases, the pressure decreases.

Question 36

Magnus Effect

Answer 36

The Magnus Effect is used to describe the effect of rotation on an object’s flight path as it moves through a fluid.
A spinning ball applied with (top spin, back spin, side spin) will have the resultant (upward, downward, sideward) force on the direction of the ball.
With spin an area of high pressure and low pressure is created and the ball will move towards the area of low pressure causing a deviation in flight path.
The pressure differential, high on one side and low on the other, creates a lift force (the Magnus force) that causes the ball to move in the direction of the pressure differential (i.e. from high to low)

Question 37

Backspin

Answer 37

Creating Backspin on the ball will ensure the ball travels with maximum distance which is an advantage in sports such as golf.

Question 38

Top spin

Answer 38

Top spin allows the ball to be hit harder with a higher velocity.
Top Spin causes the ball to bounce of the surface with a lower angle making it harder to return in racket sports such as tennis and table tennis.