biomechanics Flashcards
1
Q
what is force?
A
force is the product of mass x acceleration f=m.a
2
Q
force is the pushing/pulling effect of a body that can;
A
- get objects moving
- stop objects moving
- change the direction of a moving object
- change the speed of a moving object
- balance another force to keep an object still
3
Q
What forces are external?
A
gravity, friction, air resistance, water resistance
4
Q
what forces are internal?
A
the action of muscles and tendons on the skeletal system
5
Q
what is a frictional force?
A
a force that arises when one object or body moves across another
- friction always opposes motion and plays a large part in changing the state of motion of an object
6
Q
What are the four type of friction?
A
- static friction
- sliding friction
- rolling friction
- fluid friction
7
Q
what is static friction?
A
- friction between two objects that aren’t moving
8
Q
what is sliding friction?
A
- occurs when two objects slide over each other, eg. sand boarding
9
Q
what is rolling friction?
A
- one object rolls across another object eg. lawn bowls
10
Q
what is fluid friciton?
A
- friction caused by air or water
11
Q
what is newtons first law?
A
a body continues in its state of rest or motion unless acted upon by an external force (inertia law)
12
Q
what is inertia?
A
the term used to describe the amount of resistance to a change in an object’s state of motion
- the greater an objects inertia, the greater the force required to initiate its movement or change its state of motion
- it is directly proportional to an objects mass
13
Q
what is newtons second law?
A
- the rate of change in velocity is proportional to the magnitude of force applied. The conservation of momentum.”
f=m.a
14
Q
What happens if you apply a greater force to an object?
A
the object will accelerate at a faster rate
15
Q
what happens if the same force is applied to objects of differing mass?
A
- the object with less mass will accelerate faster
16
Q
What happens to an object with a constant mass if you increase or decrease force?
A
increasing force, increases acceleration
decreasing force, decreases acceleration
17
Q
what happens to an object if the force applied remained constant but the mass changes?
A
increasing mass, decreases acceleration
decreasing mass, increases acceleration
18
Q
what is momentum?
A
- a measure of the amount of motion possessed by a moving body and can be expressed as p=m.v
19
Q
how does the amount of force required to stop or slow down an object differ with an objects momentum?
A
an object only has momentum if it is moving
the greater its momentum, the more force required to be applied to stop/slow down the object
when 2 bodies collide, the one with most momentum will be least affected
20
Q
what does the law of conservation of linear momentum state?
A
the total momentum of 2 objects before and after impact are equal
21
Q
when does the conservation of linear momentum work?
A
- it works in a perfectly elastic collision, where no energy is lost to heat or sound
- the momentum of one object is transferred on contact to the other object, resulting in no change in total momentum, rather a transfer of momentum
- when 2 moving objects collide, linear momentum is conserved
22
Q
what is impulse?
A
impulse is equal to the change in momentum
impulse =f.t
23
Q
What is the impulse momentum relationship described by?
A
impulse =f.t
f=mass of objects x acceleration
t= length of time for which force is applied to object
24
Q
how does impulse affect an object?
A
- impulse creates momentum eg. increases the momentum of an object from 0
- changing momentum eg. increasing/decreasing momentum of a moving object
- stopping momentum eg. taking momentum back to 0
25
What happens if you increase impulse?
- increase momentum since impulse is the change in momentum
- directly proportional
- the longer a force is applied and the greater the force applied, the greater the objects impulse
26
why is impulse important in sport?
try manipulate the momentum of one of the colliding objects to produce a desired outcome eg. speed up or slow down an object
when hitting a baseball, increase force of the bat to change momentum of ball
catching a cricket ball, increase impulse by increasing time over which the ball is caught
27
how do tennis racquets change to create different impulses on the ball?
- looser strings allow for longer time for ball to be on racquet
- -> more power but less control
- tighter strings allow for quicker release as the ball is on the racquet for less time
- -> more control but less power
28
how can you increase momentum?
- ideally try to maximise both force and time but rarely happens
- large backswing ensures maximum force over a short period of time
- wide stance aims to maximise impulse by increasing contact time however force generated will be lower than a hit
29
how do you decrease momentum?
- generally wish to apply a small force over a long period of time
- catching a ball in cricket
- cheerleaders
30
what is newtons third law?
for every action there is an equal and opposite reaction
31
what does newtons third law apply to?
- applies to concept of conservation of momentum
32
how does newtons third law apply to a baseball hit?
- both baseball and bat possess a certain amount of momentum before collision
- upon collision ball explodes away while bat decelerates during follow through
- total momentum remained the same but most was transferred to the ball
33
what does the coefficient of restitution measure?
- the bounciness of a ball
- it measures the elasticity of the collision between an object and a given surface
it is the sq root of height bounced / height dropped
34
what happens if a ball is dropped and returns to the same height?
it has a coefficient of restitution of 1
35
what does the scale for COR mean for the bounciness of balls
a COR of 1 represents a perfectly elastic collision where all movement is conserves
a COR of 0 represents an imperfectly elastic collision, effectively stopping at the colliding surface
a COR of <1 means momentum is lost during the collision and rebound velocity will be lower
36
what are factors affecting the COR?
1. equipment and materials
2. temperature of balls
3. velocity of collision
37
How do equipment and materials affect the COR?
- condition of the balls, in tennis newer balls are a lot faster
- type of equipment being used- in baseball wooden bats are compulsory as aluminium have higher COR, placing pitcher in danger
- type and conditions of playing surface- clay court (high COR) vs grass (low COR)
38
how does the temperatures of balls affect the COR?
- increased temperature results in higher COR of balls
| - in squash a major difference is seen in the bounciness of the balls
39
how does velocity affect the COR?
- velocity between the oncoming ball and swinging implement will alter COR
- increased velocity increases the likelihood of the ball losing energy due to greater compression of the ball
- increased velocity= decreased COR
40
what is angular momentum?
the quantity of angular momentum possessed by a rotating body
angular momentum= angular velocity . moment of inertia
41
what is moment of inertia?
-the resistance of a rotating object to change its state of motion
MOI= mass. radius of rotation
mass= the objects mass
radius of rotation= how the mass of the object is distributed about the axis of rotation
42
what happens to MOI if you move mass away from axis of rotation?
- increase the radius of rotation and hence increase MOI
43
what happens if you move mass close to axis of rotation?
- rotation is easier to manipulate
| - makes the MOI smaller and results in and increase of angular velocity
44
Diagram of angular momentum during a dive off platform:
------------------------------------------------------------ AM
---------\ / ---------------------------\ /--------------- MOI
\ / / \
--------- / \_______________/ \--------------- AV
45
what are the two types of forces?
concentric and eccentric
46
what is a concentric force?
- force applied to produce linear motion
| - eg. float serve in volleyball
47
what is an eccentric force?
- off centre force applied to produce angular motion
| - eg. topspin serve in volleyball
48
what is the difference between angular rotation and angular motion?
angular motion is where only one eccentric force is applied to the object
angular rotation is when only one eccentric force is applied to an object but one side of the object is fixed (eg. gymnast on a bar)
49
how can you increase angular roatation?
1. increase the amount of force applied
| 2. increase distance from the axis by which force is applied
50
what are force couples?
when two equal but oppositely directed forces act on opposite side of an axis of rotation
causes the forces that produce linear motion to cancel each other out, causing the object to rotate in a fixed position
51
What is torque?
- the magnitude of a turning force
| torque= force x perpendicular distance to the axis
52
what are the 2 factors affecting torque?
1. force applied
| 2. length of moment arm
53
Where can torque be seen in sport?
in wheelchair basketball, acceleration is key so the outer rim is very large
- creates a larger moment arm and potential to create more torque
54
what are the three main parts of a lever?
- axis / pivot
- resistance
- force
55
what are the functions of levers?
- increase application of force by making the force arm longer than resistance arm
- increase speed of movement by making the force arm shorter than resistance arm
56
what is the axis?
- point around which the lever rotates
57
what is the effort/ force arm?
- distance between the fulcrum and the point at which the force is applied
58
what is the resistance arm?
- distance between axis and centre of resistance
59
What is the force produced in a lever?
the force exerted on the lever
60
what is the resistance produced in a lever?
- the force exerted by the lever
61
what is a first class lever?
- axis middle, force and resistance either side
further away the force from fulcrum , the easier to move objects
closer the force and fulcrum, greater effort required to move object
62
examples of first class levers:
not many in human body
- sea saw- effort comes from person pushing down with resistance at other end
- diving boards
63
what is a second class lever
axis is located at the end with the resistance in the middle and force applied at other end
very rare in humans
64
examples of second class levers:
push up
| wheelbarrow
65
what is a third class lever?
- axis located one end, resistance the other and force in the middle
most common in human body as we were built for speed
when looking at the body, muscle attachment represents application of force, joints are axis and weights are resistance
66
what are the 3 factors affecting the use of levers?
1. length of the lever
2. inertia of the lever
3. amount of force
67
how does the length of the lever impact the use of it?
- by lengthening, maximum velocity will be created in order to make the ball travel maximum distance
- longer the lever, greater the velocity at impact
- children cant handle long bat in cricket so shorten lever for more control
68
how does the inertia of the lever impact the use of it?
- the longer the leaver, the heavier it is and is generally more difficult to rotate
- by choking down the club in striking sports, athletes reduce the rotational inertia of the implement therefore making it easier to swing
69
how does the amount of force impact the use of a lever?
- amount of force an athlete is able to generate via their muscles determine the length of the lever the athlete should use
- longer levers are usually heavier so more force is required to move them
- important that athletes don't use longer levers if they aren't strong enough and they sacrifice control
70
what is balance?
- the ability to neutralise forces that disturb equilibrium
| - ensure you have a large stable base to ensure all segments rotate around a stable base
71
what is force motion?
- refers to the application of force to create motion
| - using newtons laws, apply each to striking for maximum velocity
72
what is inertia/moment of inertia as a biomechanical principle?
- describes the amount of resistance to a change in an objects state of motion
- goal is to reduce moment of inertia by bringing it close to axis of rotation
73
what is force-time as a biomechanical principle?
- the application of force over a period of time to change the momentum of an object
- by adopting a side on throwing position + extending the arm back during prep phase it allows for maximum distance for summation of momentum
74
what is range of motion as a biomechanical principle?
- the extent of motion around a joint
- larger ROM at shoulder ensures velocity of bat and ball can be developed over larger distance resulting in greater transfer of momentum onto the ball
75
what is optimal projection as a biomechanical principle?
when angle, velocity and height of release combine to meet the demands of the task
- if demands are to maximise distance athletes must:
- -> maximise velocity through all biomechanical principles
- -> maximise height of release without sacrificing velocity of release
76
what is spin as a biomechanical principle?
- describes the effect of rotation on an objects path as it moves through a fluid
- backspin optimises time in flight and maximises distance achieved
77
what is segmental interaction as a biomechanical principle?
- body parts are moved in segments to produce a force
- used to produce maximal force in whole body actions
eg. volleyball spike, kick in rugby
78
what is the coordination continuum? 6 steps
1. stronger and larger muscles like trunk or thighs move first, followed by smaller, faster muscles
2. sequentially accelerate each body part so that optimum passes from one body part to the next
3. each body part should be stable so the next body part accelerates around a stable base to transfer momentum
4. use as many body parts as possible so force can be applied over maximum time
5. follow through is important to prevent deceleration of last segment and safe dissipation of force
6. ensure all forces are directed towards target
79
what is fluid mechanics?
the study of forces that develop when an object moves through a fluid medium (water, air)
in some sports, fluid forces have littler effects on an objects motion (shot put)
other cases has large impact (swimming, cycling)
80
what are the 2 factors affecting fluid resistance?
density and viscosity
81
how does density affect fluid resistance?
- the more dense the fluid, the more disturbed the fluid becomes and hence the greater the resistance to change
- humid conditions present more dense conditions and therefore a ball will encounter greater levels of air resistance
82
how does viscosity affect fluid resistance?
- the more viscous the fluid (internal resistance of a fluid to flow) the more disturbed the fluid becomes and hence the greater the resistance
- honey is more viscous than water, water is more viscous than air- a swimmer experiences more viscous than a runner
83
what are the three types of drag?
form drag
surface drag
wave drag
84
factors affecting surface drag?
1. viscosity of the fluid
2. relative velocity of the moving object
3. relative roughness of surface object (this is why athletes wear tight fitting clothes in speed skating)
4. Surface area of the object (rowing or cycling, equipment has been designed to reduce size of surface area can act)
85
factors affecting form drag?
1. velocity of the object (at higher speeds, athletes experience greater levels of form drag)
2. cross- sectional area (eg. cyclist in upright vs crouched position)
3. surface roughness (rougher surfaces cause air to cling to the surface for longer periods, causing a later separation point and hence less drag)
4. shape of the object (round vs oval ball)
86
factors affecting wave drag?
1. open water (ocean) vs closed conditions (pool)
- lane ropes used to reduce wave drag by helping dissipate moving surface water
2. Technique
- by being more streamlined in the water, swimmers can reduce the effect of wave drag
- swimming underwater further reduces wave drag
- over reaching in backstroke will cause the body to move through its own waves causing resistance
3. Relative velocity of the wave:
- greater the velocity, greater the wave drag
87
what is the boundary layer?
the thin layer surrounding or "attached" to the ball
88
what are the two types of air flow?
laminar and turbulent
89
what is laminar air flow?
- smooth flow, running parallel to the ball, large turbulent pocket at back of ball
90
what is turbulent air flow?
- rough flow,
91
how does the point of boundary layer separation affect the drag on a ball?
it is where 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
- causing more drag
92
factors affecting boundary layer separation point?
MCSSsDV
Mass- greater the mass of the ball, less effect of drag
Cross-sectional area- linear relationship exists between CSA exposed to air and drag, as CSA increases so does drag
Speed- faster the ball moves, earlier boundary layer separation, large pressure differential and more drag
Surface roughness- rough surfaces create turbulent boundary layer reducing drag - dimple vs smooth ball
- rougher surfaces allow for air stream to cling to ball for longer periods, resulting in small pressure differential
Shape- round vs oval ball
- grid iron ball cuts through air cleaner than soccer ball
- oval shape encourages air stream to cling to contours of the ball
- smaller pressure differential and less drag
Drag coefficient- measure used to quantify drag or resistance of an object in a fluid environment (directly related to CSA)
```
Velocity-
low velocity (boundary layer clings to surface, separation towards rear, minor drag)
high velocity (separation occurs further forward, increased drag)
```
93
what are the environmental factors affecting drag:
HATA
1. humidity: increasing humidity increases density increasing drag
2. atmospheric pressure: increased pressure, increased density, increased drag
3. Temperature: increased temperature, decreases density, decreases drag
4. air density: higher altitude decreases drag, smaller the object, greater effect of drag
94
Sporting application of drag reduction to swimming:
- swim suit designs have helped to improve buoynacy and body position (reduce form/wave drag)
- compression of swim suit (reduces form/wave drag)
- roughness of suits means later boundary layer separation (reduce form drag)
- swim caps (reduce surface drag)
- streamlined body shape in dive (reduces form drag)
- swimmer reduces up and down movement of head ( reduces wave drag
95
sporting application of drag reduction to cycling:
- change in position of rider to bent over handlebars (reduce form drag)
- modify helmet to taper at back (reduces form drag)
- tight fitting body suit (reduces surface drag)
96
sporting application of drag reduction to ski jumping:
- ski and helmet design and tight fitting clothes have all been improved to reduce drag
97
What does Bernoullis principle state?
"An increase in velocity of a fluid results in a decrease of pressure, and a decrease in velocity of a fluid results in an increase in pressure"
98
what is the magnus effect?
- as a spinning ball moves through the air, one side of the ball will have a boundary layer of air colliding with the oncoming air. The collision causes the air to decelerate, creating a high pressure area on this side of the ball
- on the opposing side, the boundary layer of air is moving in the same direction as the air passing by so there is no collision and the air collectively moves faster. This creates a low-pressure area on the side of the ball
- the pressure differential, high on one side and low on the other, creates a lift force (magnus effect) that causes the ball to move in the direction of the pressure differential (high to low
99
definition of form drag:
when an area of high pressure and low pressure meet after a body has passed through a fluid, creating a turbulent pocket that slows the object down
100
definition of surface drag:
the resistance to forward movement through a fluid due to the interaction of the surface of the object and the fluid it is moving through
101
definition of form drag:
the drag created by the movement of water and the creating of waves as an object moves through the water
