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PE Year 12 Exam Revison > Biomechanics > Flashcards

Biomechanics Flashcards

1
Q

Newton’s first law of motion

A

A body will continue in a state of rest of uniform motion in a straight line unless acted upon by an external force

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2
Q

Newton’s second law of motion

A

The acceleration of a body is directly proportionate to the force acting on it and takes place in the direction that force acts

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3
Q

Newton’s third law of motion

A

For every action there is an equal opposite reaction

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4
Q

Force

A

The pushing or pulling action which causes the change of movement by an object/person.
F=MxA
Mass
Acceleration

Types of force:

  • concentric force/ translation - force is applied directly through the bodies centre of gravity, producing linear motion
  • eccentric force - a force applied off centre of an object, producing angular motion
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5
Q

Momentum

A

Momentum of an object is the amount of movement an object already has and is given by the product of the mass and velocity
P=MxV
Mass
Velocity

  • increase momentum by increasing velocity or increasing mass
  • an object can only have momentum if its moving
  • the greater the momentum, the larger force required to stop or slow the object
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6
Q

Conservation of momentum

A

When no external forces are applied to an already moving object its momentum can be conserved in collisions.
- Allows transfer of momentum through a stationary object being hit, the one previously moving will now stop dead while the second one now rolls away with the same momentum
Eg. Snooker balls can maintain the same momentum they had prior to collision as when they leave, if they hit nothing else

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7
Q

Impulse

A 
When a force is applied to a ball, its momentum changes. This is called impulse
I=FxT = mv- mu 
MV is mass of final velocity 
MU is mass of initial velocity 
Measured in Newton seconds (Ns)

Impulse-momentum relationship can also be called Newton’s second law
Eg. A hockey player will drag the ball out for as long as possible to maximise impulse of the ball and produce the greatest momentum.

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8
Q

Accuracy

A

Height accuracy is moving hand, leg or bat in a straight line to the target

Sideways accuracy is passing the object in line with target again and can be maximally attained through flattening the arc so there is less deviation away from the target and more chance of hitting it

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9
Q

Elasticity (Coefficient of restitution)

A

The bounciness of a ball or springiness of a striking implement and is measured in 3 different ways:

COR= height of rebound / height of drop

COR= V1 / V0
V0 is initial velocity
V1 is velocity after collision

C= S2-V2 / V1-S1

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10
Q

Angular motion

A

If the line of action does not pass through the centre of an object then the object will be rotated as it moves
Unless a body is fixed at some point, any rotation occurs about an axis passing through its centre of gravity

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11
Q

Moment of inertia

A

Moment of inertia is the resistance to rotational motion
The greater the moment of inertia, the greater the force or turning effect (torque) required to impart the same angular acceleration in the body.
Eg. Figure skater reduces moment of inertia by tucking in her arms from being outstretched
I = MR^2
M is mass
R is radius of rotation

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12
Q

Angular momentum

A

Is the quantity of angular motion passed by a body

When moment of inertia is high, angular velocity is low - vice versa

Angular momentum = angular velocity x moment of inertia

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13
Q

Levers

A

Rigid, bar-like objects that turn about a fixed point (a fulcrum or axis)
Three main parts to a lever:
- an axis/fulcrum (the pivot point)
- a resistance/load (the object being moved)
- a force (the action causing the load to move)

Three different types:

  • First class
  • Second class
  • Third class
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14
Q

First class lever

A

Have the fulcrum/pivot point located between the resistance and the point of force application.
Eg. A seesaw or a javelin being thrown and using the elbow as the pivot, hand as the load because its carrying the javelin and then the force is the tricep

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15
Q

Second class levers

A

Have the fulcrum at the end of the lever with the resistance/load is in the middle while the force is at the other end
Eg. A wheelbarrow or when you stand on your tiptoes with the fulcrum as the ball of your feet. Volleyball players use this a lot

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16
Q

Third class levers

A

Have the fulcrum at the end again with the force in the middle this time and the load/resistance is at the other end.
Eg. Performing a bicep curl or kicking a soccer ball… the most common lever in the body while its the most impractical

17
Q

Resistance and force arms

A 
Resistance/load arm is the distance from the load to the fulcrum
Eg. The hand to the elbow in a third class lever

The mechanical advantage/disadvantage is the term to describe the relative efficiency of a lever system

Mechanical advantage= Force (effort) arm / Resistance arm

When the effort arm is longer than the resistance arm there is a mechanical advantage

18
Q

Torque

A

The measure of a turning effect of a couple of forces is known the torque.

T= Fx
F is the magnitude of one of the forces
X is the shortest, or perpendicular distance between the lines of action

19
Q

Factors affecting levers

A
  1. Length of lever
  2. Inertia of lever
  3. Amount of force
20
Q

Quantitive and Qualitative analysis

A

Quantitative involves looking at the numbers in data like seconds or metres.
Eg. Taking a skinfolds test

Qualitative is subjective and is for the coach a judgment call.
Eg. Statements by a television commentator on a bowling technique in cricket

Four stage qualitative analysis:

  1. Preparation
  2. Observation
  3. Diagnosis
  4. Intervention
21
Q

Biomechanical Principles of movement

A
  1. Force - motion
    - looks at the effect of unbalanced forces on movement
    - Based on all three of newtons laws
  2. Force - time
    - Newton’s second law of motion, also known as the impulse - momentum relationship
  3. Inertia
    - A body at rest will remain at rest until a force acts on it to move it. Same for a moving object having external force on it to slow it down or speed it up
  4. Range of motion
    - relates to the type of motion, angular or linear, of body segments used to execute a movement
  5. Balance
    - Centre of gravity
    - Stability - the bigger the base of support, the greater the stability - You can improve stability by increasing the base of support, lowering the centre of mass, increasing the mass of the body
    - Equilibrium and balance - stable, neutral or unstable Equilibrium, dynamic or static balance
  6. Coordination continuum
    - sequential - low force / high speed and with largest to smallest muscle recruitment
    - simultaneous - high force (strength) and with muscles recruiting together
  7. Segmental interaction
  8. Optimal projection
    - 45 degrees is optimal but can be less if you are releasing from above the ground at shoulder height for example
  9. Spin
    - more detail on another card
22
Q

Magnus effect

A

Magnus effect

  • the effect of rotation on an objects body as it moves through the air
  • Top spin, side spin and back spin are all a result of the Magnus effect because it shows that when a ball is spinning with top spin for example, the direction of spin is forward and down from top to bottom so the pressure differential is high at the top of the ball because the spin is head on with the wind but low at the bottom because the spin is going with the wind. It results in Magnus force to pull the ball down and drop meaning players can hit the the ball harder with top spin and it still go in.
23
Q

Bernoulli’s principle

A
  • idea behind the Magnus effect
  • where the spin of the ball clashes with the wind, there is high pressure, low velocity
  • where the spin of the ball is in the same direction as the wind, there is low pressure and high velocity
  • this is reversed for the flight of a discus or aeroplane wing as the high pressure is below the wing and is trapped there in a pocket.
  • it wants to escape and get to the low pressure much like air escaping from a balloon above the wing so it gives the plane and discus lift pushing up from underneath the wing.
24
Q

Fluid mechanics

A 
Looks at the fluids and the forces that act on objects 
The forces include:
- Buoyancy
- Drag
- Lift

Fluid dynamics is the study of fluids in motion which is the way liquids and gases move or flow.

25
Q

Laminar and Turbulent flow

A

Laminar flow is the flow of air or liquid in a straight line
- generally associated with low velocity, streamlined objects

Turbulent flow is the flow of air or liquid in circles or chaotic lines that go all over the place much like being told to belt up for the bumps on a plane
- Eddies, vortices and wakes are all associated with turbulent flow

Boundary layer is the layer of air around or attached to the ball

26
Q

Drag

A

A fluid friction force

  • it is the resistance to motion of an object or body moving through a fluid
  • acts in the same direction as the flow of the fluid moving past an object and in the opposite direction to that of the body or object

Total drag = pressure drag + surface drag + wave drag

27
Q

Pressure/Form drag

A
  • resistance created by pressure differential between front and back of moving object through fluid
    Factors affecting:
  • cross sectional area of the object in the fluid
  • velocity of the object
  • surface roughness
  • shape of the object
28
Q

Surface drag

A 
- Friction produced between fluid and surface of a moving object
Factors affecting:
- velocity of moving object 
- roughness of surface of object
- viscosity of fluid
- surface area of the object
29
Q

Wave drag

A 
- resistance formed by creation of waves at the point where air and water interact
Factors affecting:
- velocity of wave
- technique 
- open water vs closed water

PE Year 12 Exam Revison (5 decks)

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