Biomechanics (1.3) Flashcards
(90 cards)
1
Q
What’s Newton’s 1st law
A
- Law of inertia
- An object will remain at rest or at constant velocity, unless acted upon by an external force (forces) (friction, gravity, air resistance, force form another human)
E.g. football will remain on penalty spot until kicked
2
Q
What’s Newton’s 2nd Law
A
- Law of acceleration
- The rate of change of velocity is directly proportional to the size and direction of the force
E.g. acceleration of a netball during a pass is proportional to the force from the players hands and is in the same direction as the force
3
Q
What’s Newton’s 3rd Law
A
- Law of reaction
- Every action has an equal and opposite reaction
E.g. when a player jumps for a header, they push downwards on the ground (action force) and th ground pushes upwards on the player (normal reaction force)
4
Q
If two or more forces act in the same direction what happens
A
The 2 forces are combined
5
Q
If two or more forces act in opposition to each other what happens
A
They have a cancelling effect
6
Q
What’s a balanced force
A
When two or more forces acting on a body are equal in size but opposite in direction. All forces cancel out
7
Q
What’s an unbalanced force
A
When two or more forces acting on a body do not cancel out. This means a net force acts
8
Q
What’s a net force
A
The overall force acting on a body when all forces are considered. Also, known as the resultant force
9
Q
External forces originate from outside the body.
There are 4 external forces that may act
What are they and define them
A
- Weight= Acts downwards from centre of mass
- Reaction= Acts upwards from the points of contact with the ground, in reaction to all downwards forces
- Friction= The force opposing the sliding motion of one surface across another
- Air resistance= The force acting to oppose the motion of a body through air
10
Q
- What are the 2 vertical forces
- What are the 2 horizontal forces
A
Vertical forces= Weight and Reaction
Horizontal forces= Friction and air resistance
11
Q
Factors affecting friction
A
- Roughness of surface (sole of footwear)
- Roughness of surface (playing surface)
- Temperature (heated tyres increase friction between the rubber and the track)
- Weight
12
Q
Friction can be maximise by
A
- Increasing roughness of either of the surfaces. E.g. studded football boots, dimpled netballs, roughened surface of swimming blocks
- Increasing mass / downforce. E.g. select heavy rugby pack, rear spoiler on F1 car
- Increasing temperature (of some material). E.g. using tyre heaters
13
Q
Fiction can be minimised by
A
- Increasing smoothness of surface. E.g. wax skis, melt and re-freeze ice rink
14
Q
Define air resistance
A
The force acting to oppose the motion of a body through air
15
Q
4 Factors affecting air resistance
A
- Velocity
- Frontal-cross sectional area
- Streamline and shape
- Surface Characteristics (smoothness)
16
Q
Air resistance has less effect on the motion of objects with large or small mass
A
Air resistance has less effect on motion of objects with larger mass
17
Q
Air resistance can be minimised by
A
- Reducing Frontal-cross sectional area. (E.g. downhill skier adopts crouched position, rather than upright)
- Using a streamlined shape. (E.g. ski jumper in flight has an aerofoil shape)
- Making surfaces smooth. (E.g. cycling suits and helmets designed to minimise turbulence (chaotic air flow))
- Decreasing velocity also minimises air resistance
18
Q
What needs to be put on a free body diagram
A
- Direction of movement (DOM)
- Air resistance
- Ground force
- Weight
- Circle for Centre of mass
-Sometimes direction of friction
19
Q
Define force
Formula for force
Unit of measurement
A
- A push or pull that tends to alter state of motion of a body
- F= mass x acceleration (F=ma
- Measured in Newton’s (N)
20
Q
Define momentum
Formula for momentum
Unit of measurement
A
- The amount of motion possessed by a moving body
- Momentum= mass x velocity
- Kilogram metres per second (Kgm/s)
21
Q
Define acceleration
Formula for acceleration
Unit of measurement
A
- The rate of change in velocity
- Acceleration= final velocity - initial velocity / time
OR
Acceleration= Force / mass - Metres per second squared (m/s2)
22
Q
Define weight
Formula for weight
Unit of measurement
A
- The gravitational force that the earth exerts on the mass of the body
- W= Mass x acceleration due to gravity (W= mg)
- Newton’s (N)
23
Q
Define centre of mass
A
The point at which a body is balanced in all directions and from which weight appears to act
24
Q
The position of centre of mass is affected by what 2 factors
A
- Shape
- Density of different parts of the body
25
Why does Centre of mass change position in a performers body
Because the centre of mass must be at the point where the mass is balanced around it in all directions
E.g. if a performer raises their arms above head in take off phase before high jump, centre of mass also raises
26
Define stability
A measure of how easily a body is moved from a position of balance
27
Define line of gravity
An imaginary line extending vertically downward to the ground from the centre of mass
28
Define base of support
The area enclosed by the points of contact
29
4 ways to improve stability
- Low Centre of mass
- Large base of support
- Line of gravity in middle of base of support
- Large mass
30
Define the load (force) on a lever
The weight or resistance of the lever arm and anything that’s attached to it
31
Define the effort (force) on a lever
The force of muscle contraction applied to move the lever
32
Define the fulcrum
The pivot or fixed point about which the lever moves
33
What’s the effort arm
The (perpendicular or right angle) distance between the effort and fulcrum
34
What’s the load arm
The (perpendicular or right angle) distance between the load and fulcrum
35
What causes a mechanical advantage in levers
- When the effort arm is greater than the load arm (the effort is further away from the fulcrum)
- Then less effort force is needed to move the load and/or a greater load can be moved
36
What class lever has a mechanical advantage
Second class levers
37
What’s limb kinematics
Study of movements of limbs in space, and time taken to carry out the movements. Includes the study of gait (how someone moves)
38
Limb kinematics in action. How’s it carried out
- Reflective markers place on performers bony landmarks and they’re filmed using multiple video analysis.
- Data’s transferred to digital format for analysis
39
Benefits and drawbacks of limb kinematics
Benefits= -Data immediately available and accurate
- Coaches can use the analysis to improve technique
- Examine causes of common injury, which can be prevented as poor technique is identified
- Investigates impact of equipment on technique, so helps with selection of appropriate equipment
Drawbacks= -Equipment is expensive
- Laboratory conditions make some techniques difficult to perform due to lack of space
- Results don’t take into account individual differences
40
What are force plates
A platform that measures all of the forces applied when a performer stands, steps across or jumps on it
41
Force plates in action. How’s it carried out
- Platform measures the ground reaction forces that the performer generates
- Data is generated including force time graph, power and acceleration information
42
Benefits and drawbacks of force plates
Benefits= -Fast and accurate results generated
- Analysis of gait and take off and/or landing technique, which can be used to identify technique and efficiency improvements
- Results are useful to plan conditioning or development programmes
Drawbacks= -Equipments expensive
-Laboratory conditions make some techniques difficult to perform. E.g. high jumper finding it hard to replicate run up technique of asked to take off from platform
43
What are wind tunnels
A chamber through which air is forced
44
Wind tunnels in action. What do they do
- The object or performer to be test is placed in the tunnel.
- A controlled flow of air is forced through, and the air flow around the object is studied to measure resistance around it
45
Benefits and drawbacks of wind tunnels
Benefits= -Equipment and technique can be adapted to increase aerodynamic properties
- Wind speed and direction are controllable to mimic competitive conditions
- Individual pieces of Equipment can be teased. E.g. cycle helmets
Drawbacks= -Wind tunnels are expensive and located In labs
-Real life conditions may impact unexpectedly, so results not always realistic
46
Define linear motion
Movement of a body in a straight or curved line, where all parts move the same distance, in same direction over the same time
- E.g. skeleton bob rider hitting final straight at top speed will have all body parts travelling in same direction, over same distance per unit of time
47
Linear motion occurs as a result of a...
Direct force being applied to a body
48
What’s a direct force
An external force that passes through the centre of mass
49
# Define distance
And an example
- The total length of the oath covered from start to finish
- Measured in metres (m)
E.g. distance covered by Usain Bolt in 100m final is 100m, swimming 4 lengths of a 50m pool is 200m
50
# Define displacement
And an example
- The shortest straight-line route from start to finish
- Measured in metres (m)
E.g. the displacement of a swimmer swimming 4 lengths of a 50m pool would be 0m as they finish where they started
51
# Define speed
formula
Unit of measurement
- The rate of change in distance
- Distance / time taken
- measured in metres per second (m/s)
52
# Define velocity
Formula
Unit of measurement
- The rate of change in displacement
- displacement / time taken
- metres per second (m/s)
53
# Define acceleration
Formula
Unit of measurement
- The rate of change in velocity
- (final velocity - initial velocity) / time taken
- metres per second squared (m/s2)
54
Graphs of linear motion
Describe a distance/time graph
- Shows the distance a body travels over a period of time
- Gradient of curve indicates the speed of the body, and will show whether the body is at rest, travelling with constant speed, accelerating or decelerating
- flat line= rest
- straight diagonal line(upwards)= constant speed
- curved line upwards= acceleration
- curved line going flat= deceleration
55
Describe a speed/time graph
- Shows the speed of a body over a period of time
- Gradient indicates whether body is at rest, travelling at constant speed, accelerating or decelerating
- The area under the speed/time curve is equal to the distance travelled by the body
56
Describe a velocity time/graph
- Shows the velocity of a body over time
- Gradient of curve indicates the acceleration of the body at a particular instant and shows whether the body is at rest, travelling with uniform velocity, accelerating or decelerating
- Using velocity/time curve, accelerating can be calculated at any given point using the accelerating formula: (final velocity-initial velocity) / time taken
- Velocity/time curve also shows any change in direction the body makes
- Negative curve below horizontal axis represents a change in body’s direction
57
Define angular motion
Movement of a body or part of a body in a circular path about an axis of rotation
58
What causes angular motion
Eccentric force
59
What’s an eccentric force
An external force passes through the outside of the centre of mass
- which can also be referred to as a torque
60
Angular motion is measured in what
And what does it measure
- Angular motions measured in radians (rad)
| - Angular motion is a measure of the angle through which a body rotates
61
3 angular motion descriptors
1) Define angular velocity
Formula for it
The rate of change in angular displacement or simply rate of rotation
-Angular velocity = angular displacement/time taken
62
2) Define moment of inertia
Formula for it
The resistance of the body to change its state of angular motion or rotation
Moment of inertia= mass x distribution of mass from the axis of rotation
- measured in kilograms metres squared (kgm2)
63
Factors affecting moment of inertia
- Mass (kg)
| - Distribution of mass from the axis of rotation
64
Describe how mass and distribution of mass affects moment of inertia
- Greater the mass of the body, the greater the moment of inertia. E.g. gymnasts and divers have low mass as it requires a high degree of rotation
- Further the mass moves from the axis of rotation, the greater the moment of inertia. E.g. movements where mass is tucked in around the axis, they’ll rotate quicker due to low moment of inertia
Moment of inertia is low, then angular velocity is high
65
Describe Moment of inertia’s direct effect on angular velocity
- If moment of inertia is high, then resistance to rotation is high and therefore angular velocity is low (spin slowly)
- If moment of inertia is low, then resistance to rotation is low and therefore angular velocity is high (spin fast)
66
3) Define angular momentum
Formula for it
The amount of angular motion of a rotating body
- Angular momentum= moment of inertia x angular velocity
67
Define angular analogue of Newton’s 1st law of motion
A rotating body will continue to turn about the axis of rotation with constant momentum unless acted upon by an eccentric force or external torque
68
How is angular momentum created for a skater
By using a curve on approach to increase speed
69
How can a skater go from a curve to a spin so quickly
The distance from the axis of rotation is decreased, therefore reducing the moment of inertia
70
What does a skater do before leap and after/during landing
Stick limbs are out to give High moment of inertia and low angular velocity, which gives more balance
71
Define air resistance
The Force acting to oppose the motion of a body through air
72
Define drag
The force acting to oppose the motion of a body through a fluid
73
Air resistance and drag are both types of what
Fluid friction
74
What are the factors that impact the air resistance and drag
1) Velocity= Greater velocity, greater air resistance/drag
2) Mass= Greater the mass, the less it’s changed by these forces
3) Frontal-cross sectional area= Smaller this area is, the less fluid friction
4) Streamlining and shape= Fluid friction minimised by optimal shape. E.g. cyclist using crouched position
5) Surface characteristics= Smooth surfaces create less fluid friction. E.g. swimmer shaving body hair
75
Define a projectile
A body that is moving within a fluid, Not in contact with the ground.
- Fluids include air and water
76
Three release factors affecting horizontal distance
And explain them
1) Height of release= Level from which a projectile is released compared to level of landing surface. Higher the height of release, further the horizontal distance travelled
2) Speed of release= How Fast a body is travelling at the moment it becomes a projectile. Greater the speed of release, further the horizontal distance travelled
3) Angle of release= Projection angle of object, measured between horizontal and direction of projectile at release. Optimal angle is 45 degrees if height of release is same as landing
77
What’s a free body diagram
A pin diagram showing external forces acting on a body
78
Describe weight on a free body diagram
- acts vertically downwards from the COM
| - size of W arrow depends on mass
79
Describe air resistance on a free body diagram
- acts in the opposite direction to the direction of motion, drawn from COM
- Size of AR arrow depends on factors affecting AR: velocity, frontal-cross sectional area, streamlining/shape and surface characteristics
80
# Define parabolic
Define non-parabolic
Parabolic= Symmetrical flight path
Non-parabolic= Non-symmetrical flight path
81
Define aerofoil
A streamlined structure with at least one curved surface (facing upwards)
82
Define angle of attack
Angle at which a projectile is presented to the air
83
What’s Bernoulli’s principle
Faster fluids flow, the less pressure they exert. The slower fluids flow, the more pressure they exert. This can create a lift force on a projectile
84
How’s a upwards lift force created
- Air travels further and faster above the projectile creating low pressure
- Air travels less far and slower below the projectile creating high pressure
- The Pressure differential causes an upwards lift force from high to low pressure
85
What’s a reverse aerofoil
An aerofoil positioned with its curved surface facing downwards and its flatter surface facing upwards causing downforce
86
How’s a downwards force created
| Bernoulli’s downforce
- Air travels less far and slower above the projectile creating high pressure
- Air travels further and faster below the projectile creating low pressure
- The Pressure differential causes a downwards force from high to low pressure
E.g. on an F1 car
87
What creates spin
An eccentric force
88
What are the 4 types of spin
Describe them
1) Top spin= when a ball is rotating around its transverse axis, with the top spinning in same direction as it’s motion
2) Back spin= when a ball is rotating around its transverse axis, with the top spinning in the opposite direction to its motion
3) Hook= (for a right sided performer) when the front of the ball spins to the left, around its longitudinal axis. E.g. inside of right foot
4) Slice= (for a right sided performer) when the front of the ball spins to the right, around its longitudinal axis. E.g. outside of right foot
89
What’s the Magnus force
| Same as Bernoulli principle, but for a ball
Force caused by a pressure differential on either side of a spinning projectile
90
Describe the magnus force for a top spin
1) Top of Ball, air flow is in opposite direction to spin. Slows the air and causes high pressure
2) Under the ball, air flow is in same direction as spin. This speeds up air and causes low pressure
3) Pressure differential is formed. Higher pressure above the ball than below, causing a downwards force called Magnus force. This causes ball to dip, causing a shorter flight path.
Opposite for back spin, longer flight path
