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PE Studies > Biomechanics > Flashcards

Biomechanics Flashcards

1
Q

Newtons Second Law of Acceleration

A
  • The rate of acceleration of a body is proportional to the force applied to it, and inversely proportional to the mass of the object
  • Larger force = faster acceleration
  • Force = mass x acceleration
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2
Q

Newtons Third Law of Action and Reaction

A
  • For every action, there is an equal and opposite reaction
  • When two objects exert a force upon each other, the forces are opposite in direction and equal in magnitude
  • Eg. During a backstroke start, swimmers exert a force against the wall, which results in an equal and opposite force back on the swimmer, allowing the swimmer to push off with great force
  • Applies to the concept of conservation of momentum
  • An equal and opposite force occurs when two objects collide, causing a transfer of momentum between the objects
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3
Q

Momentum

A
  • The quantity of motion of a moving object
  • Momentum = mass x velocity
  • Increased mass or velocity of object results in increased momentum
  • Has momentum when moving
  • The greater the momentum the more force required to stop it
  • When two bodies collide, the one with the most momentum will be affected the least
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4
Q

Conservation of Linear Momentum

A
  • Total momentum before and after impact are equal
  • Perfectly elastic collisions (no energy lost in sound or heat)
  • Momentum is transferred to another object upon contact
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5
Q

Impulse

A
  • Change in momentum of an object
  • Impulse = force x time
  • The longer the force is applied and the greater the force, the greater the impulse
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6
Q

Flattening the Arc

A
  • Good technique can increase contact time with the ball
  • Can increase application of force in desired direction
  • Increased accuracy often with a decrease in force
  • A more curved arc reduces the likelihood of successful hits due to limited opportunities to apply force in a particular direction
  • Flattening the arc increases likelihood of applying force in the desired direction creating a zone of flat like motion
  • Eg. A batsman in cricket flattens the arc by shifting body weight forwards, rotating the body and moving the bat in a straight line towards the target
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7
Q

Coefficient of Restitution

A
  • The elasticity of the collision between an object and a given surface
  • Measures how much energy remains in the object after collision
  • Elasticity is the measure of how much rebound exists following a collision
  • COR of 1 = perfectly elastic collision
  • COR of 0 = perfectly inelastic collision (no movement eg.Play dough)
  • COR = the square root of (height bounced/height dropped)
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8
Q

Factors Affecting the Coefficient of Restitution

A
  1. Equipment and Materials
    - Condition of the balls
    - Type of equipment
    - Type and condition of playing surface
  2. Temperature of the Balls
    - Increase in temp results in an increase in COR
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9
Q

Types of forces

A

Concentric Force: applied to produce linear motion (flat serve in volleyball)
Eccentric Force: off centre force applied to produce angular motion (top spin serve)

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10
Q

Angular Rotation

A
  • Caused by the application of an eccentric force
  • When 1 eccentric force is applied both linear and angular motion occur
  • To increase angular rotation, increase the amount of force applied or increase the moment arm (distance from application of force to axis of rotation)
  • Force Couples: two equal forces, oppositely directed act on opposite sides of an axis of rotation
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11
Q

Torque (Nm)

A
  • The magnitude of a turning force
  • Torque = force x perpendicular distance of lever arm
  • Distance from where Force is applied to where torque is produced is the moment arm
  • Longer moment arm = greater rotational force
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12
Q

Angular Momentum

A
  • The quantity of angular motion possessed by a rotating body
  • Angular momentum = angular velocity x moment of inertia
  • Angular velocity: the velocity or speed of a rotating object
  • Moment of inertia: the resistance of a rotating object to change its state of motion
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13
Q

Moment of Inertia

A
  • A quantity expressing a body’s resistance to angular acceleration
  • Moment of Inertia = mass of the object x radius of rotation
  • Radius of rotation: how the mass of the object is distributed about the axis of rotation
  • Bringing mass close to axis of rotation makes the moment of inertia smaller and increases angular velocity
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14
Q

Moment of Inertia Examples

A
  • By moving the mass of the object further away from the axis of rotation, you increase its radius of rotation and therefore, increase its moment of inertia
  • By moving a batters hands further down the handle, control is increased and moment of inertia decreased as the mass of the bat is closer to the axis of rotation
  • Runners flex at their knee to reduce the legs moment of inertia. The mass of the leg is moved close to the hip (axis of rotation) and the thigh is pulled forwards with greater velocity
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15
Q

Conservation of Angular Momentum

A
  • The spinning body will continue spinning indefinitely unless an external force acts on it
  • From the time the diver leaves the board to the time he enters the water, his angular momentum will be conserved as no external forces are acting in him
  • At the commencement of the dive, his body position is very open, resulting in a large moment of inertia and low angular velocity
  • As the diver moves into a tuck position, he decreases his moment of inertia and increases his angular velocity
  • At the end of his dive, as he prepares to enter the water, he extends his body, moving his mass away from his axis of rotation, increasing his moment of inertia and reducing his angular velocity
  • To increase angular momentum prior to performance increase linear momentum transferred to angular momentum or improve segmental interaction
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16
Q

Levers

A
  • A bar that rotates around a fixed point used to apply force against a resistance
  • Weight or resistance to be moved
  • Axis or pivot point
  • Application of force to move resistance
  • Increase application of force by making the force arm longer than the resistance arm
  • Increase speed of movement by making the resistance arm longer than the force arm
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17
Q

First Class Levers

A
  • Axis in the middle
  • The further away from the axis that the force is applied, the easier it will be to move (crow bar)
  • The closer the applied force to the axis, the greater the force needed
  • Eg. Seesaw
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18
Q

Second Class Levers

A
  • Resistance in the middle

- Eg. push up or wheelbarrow

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19
Q

Third Class Levers

A
  • Force in the middle
  • Large resistance arm ensures increased speed and greater force is applied
  • In the human body the muscle attachment is the force, the joint is the axis and the resistance is the weight
20
Q

Factors Affecting the Use of Levers

A
  1. Length of the lever
    - Velocity is greatest at the distal end of a lever
  2. The inertia of the lever
    - The longer the lever, the heavier it is, making it more difficult to rotate
    - By holding the handle further down, rotational inertia is decreased and it is easier to swing
  3. The amount of force
    - More force is required when using longer levers (length depends on athletes muscle force)
  4. A smaller force can balance a larger resistance when the force arm is longer than the resistance arm
  5. A force can move a resistance arm through a greater range of motion when the force arm is shorter than the resistance arm
21
Q

Fluid Mechanics

A
  • The study of forces that develop when an object moves through a fluid
  • Drag
  • Lift
  • Buoyancy
22
Q

Fluid Resistance

A
  • The transfer of energy from object to fluid caused by the disturbance of a moving object through a fluid
  • When an object moves through a fluid it is disturbed
  • The greater the disturbance, the greater the Transfer of energy from object to fluid
23
Q

Factors Affecting Fluid Resistance

A
  1. Density
    - The more dense the fluid, the more disturbed the fluid becomes and creates greater resistance (humidity will cause greater levels of air resistance)
  2. Viscosity
    - The more viscous the fluid (internal resistance of a fluid to flow), the more disturbed the fluid becomes and hence the greater the resistance (swimmers experience more resistance than runners as water is more viscous than air)
24
Q

Surface Drag

A

The friction produced between fluid and the surface of a moving object

25
Q

Factors Affecting Surface Drag

A
  1. Relative velocity of moving object
  2. Relative roughness of surface object
    - Wearing tight fitted clothing, shaving and wearing lotions reduce surface friction
  3. Viscosity of the fluid
  4. Surface area of the object
    - Rowing and cycling equipment is designed to reduce the size of the surface area in contact with the fluid
26
Q

Form Drag

A

Resistance created by pressure differential between front and back of an object moving through a fluid

27
Q

Factors Affecting Form Drag

A
  1. Cross sectional area (CSA) of the object presented to the fluid
    - Eg. Cyclist in upright versus crouched position
  2. Velocity of the object
    - At higher speeds, athletes experience greater levels of form drag
  3. Surface Roughness
    - Rougher surfaces cause the air to cling to the surface for a longer period, causing a later separation point and hence less drag
  4. Shape of the object
    - Eg. Round ball versus and oval ball
28
Q

Wave Drag

A
  • Resistance formed by the creation of waves at the point where air and water interact
  • Major form of drag acting on a swimmer
29
Q

Factors Affecting Wave Drag

A
  1. Relative velocity of the wave
    - Greater the velocity, greater the wave Drag
  2. Technique
    - By being more streamlined in the water, swimmers reduce the effects of wave drag
    - Swimming underwater further reduces wave drag
  3. Open water versus closed conditions
    - Lane ropes used to reduce wave drag by helping to dissipate moving surface water
30
Q

Boundary Layer

A
  • Thin Layer of air surrounding or attached to the ball
  • Laminar (smooth flow, large turbulent pocket at the back of the ball)
  • Turbulent (rough flow, small turbulent pocket at the back of the ball)
31
Q

Boundary Layer Separation

A
  • Where the boundary layer breaks away from the ball
  • The earlier the boundary layer separation, the greater the pressure gradient between the front and back of the ball which leads to increased drag
32
Q

Factors Affecting Boundary Layer Separation Point

A
  1. Velocity
    - Low velocity: boundary layer clings to the surface, separation well towards the rear will minor drag
    - High velocity: separation occurs further forwards which increases drag
  2. Surface Roughness
    - Rough surfaces create turbulent boundary layers, reducing the effect of drag
    - Eg. Dimpled golf ball versus smooth golf ball
    - Swim suits allow rough surfaces creating a turbulent boundary layer resulting in late separation and reducing the effect of drag
33
Q

Factors Affecting Drag

A
  1. Drag Coefficient
    - Measure used to quantify the drag or resistance of an object in a fluid environment
    - Directly related to cross sectional area
  2. Cross Sectional Area (CSA)
    - Linear relationship between CSA exposed to air and drag
    - Increase CSA = increased drag
  3. Speed
    - The faster the ball moves through the air, the earlier the boundary layer separates from the ball creating a large pressure differential between the front and back rear of the ball and hence more drag
  4. Surface Roughness
    - Rougher surfaces allow for the air stream to cling to the ball for longer periods, resulting in smaller pressure differentials between the front and back of the ball and hence less drag
  5. Mass
    - Greater the mass of the ball, the less the effect of drag
  6. Shape
    - Round ball versus an oval ball
    - Gridiron ball cuts through the air more cleanly than a soccer ball
    - Oval shaped ball encourages the air stream to cling to the contours of the ball to the end of the tail
    - Result is smaller pressure differential between front and back of ball and therefore less drag
34
Q

Environmental Factors Affecting Drag

A
  1. Air Density
    - Higher altitude, decreased drag
    - The smaller the object, the greater the effect
    - Eg. Easier to hit a home run in higher altitude
  2. Atmospheric Pressure
    - Increased pressure, increased density, increased drag
  3. Humidity
    - Increased humidity, increased density, increased drag
  4. Temperature
    - Increased temperature, decreased density, decreased drag
35
Q

Buoyancy

A
  • The upward force that keeps things afloat
  • Counteracts the effects of gravity
  • How well a body floats or how high it sits in the fluid
36
Q

Buoyancy Archimedes Principle

A

The buoyant force acting on an object is equal to the weight of the fluid displaced by the object

37
Q

Positive Buoyancy

A

Displaces a volume of fluid equal to or greater than its weight and will float. A swimmer with positive buoyancy experiences less fluid resistance than a swimmer who is less buoyant. Positive buoyancy makes it easier to streamline which decreases the drag forces on the swimmer.

38
Q

Negative Buoyancy

A

Displaces a volume of fluid less than its own weight and sinks

39
Q

Neutral Buoyancy

A

When an object will neither sink or float but remains suspended in the fluid

40
Q

Lift Forces

A
  • The component of force that acts perpendicular to the direction of flow
  • Acts at right angles to the direction of motion (upwards/downwards)
  • Only occurs in objects which are spinning or not perfectly symmetrical
  • Lift is created by different pressures on opposite sides of an object due to fluid flow past the object
41
Q

Examples of Lift Forces

A
  • Airplane wings create Lift in an upwards direction to keep it in the air
  • Racing cars create a lift downwards to keep it on the ground
42
Q

Bernoulli’s Principle

A
  • Velocity is inversely proportional to pressure
  • To maximise distance the appropriate angle creating sufficient lift whilst presenting limited CSA minimising drag must be found
43
Q

Magnus Effect

A
  • Describes the effect of rotation on an object’s path as it moves through a fluid
  • Applies to Bernoulli’s principle to explain the effect spin has in the trajectory of flight bath of an object
44
Q

Newton’s First Law

A

States that an object in motion will stay in motion unless acted upon by an external force

45
Q

Projectile Motion

A

A form of motion in which an object travels on a curved path

46
Q

Balance

A

The ability to maintain the line of gravity of a body within the base of support. Benefits as segmental interaction can occur

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