Class Test 4 Flashcards
(119 cards)
1
Q
Define friction
A
The force that comes whenever one body or object moves across the surface of another body
2
Q
Why might you want friction in sport?
A
To remain stable or secure
3
Q
Why might you want small friction forces
A
To move for quickly, like agility
4
Q
Describe limiting friction
A
When there is a limit to the frictional force that can restrict the movement of objects
5
Q
What is the equation for limiting friction
A
The coefficient of limiting friction x perpendicular reaction force from the surface
6
Q
Give two surfaces the coefficient of friction depends on
A
- Material of surface
2. Roughness of surface
7
Q
Define sliding friction
A
The frictional force between two surfaces when there is movement between the two surfaces
8
Q
What is sliding friction sometimes known as?
A
Dynamic friction
9
Q
What is the equation for sliding friction
A
Coefficent of sliding friction x perpendicular reaction force
10
Q
Define rolling friction
A
The friction between two surfaces when the object is moving in a rolling fashion
11
Q
What can influence rolling friction?
A
- Weight
- Radiance of rolling object
- Surfaces deformability (ability to change shape)
- Coefficient of friction
12
Q
Is the friction of rolling friction smaller or bigger than sliding/static?
A
Rolling friction is much smaller- around 100-1000 times smaller
13
Q
What does it mean that rolling friction is so much smaller than sliding and static friction?
A
This means it’s much easier to move objects that are affected by rolling friction.
14
Q
Give an example of rolling friction
A
Whether a golf ball will roll on grass or not will depend on whether the surface is wet or dry, hard or soft, the length of the grass and the way the grass is lying
15
Q
Describe object static (in relation to magnitude)
A
The magnitude of limiting friction is equal to the force that causes an object to slide. if an object is static then the same force is being applied to try to make the object move, as is the friction to make it stop. as the force applied increases, limiting friction increases
16
Q
What happens to the magnitude of friction when the force on an object increases?
A
The magnitude of friction will be equal to the force trying to move the object. this is until the limiting frictional force reaches its upper limit and friction can no longer increase
17
Q
What happens to the magnitude of friction when an object starts moving
A
If an object starts moving it means that the force making the object move is bigger than the frictional force trying to stop it moving
18
Q
Is it easier to push or pull an object
A
Pull an object
19
Q
Why is it easier to pull rather than push
A
Because when you push an object you are directing the force downwards.
20
Q
Is friction greater when pulling or pushing
A
When pushing- making it harder to push an object
21
Q
For an object to remain still on a slant what must happen?
A
The friction must be greater than the component of the weight along the surface
22
Q
What happens if the coefficient is larger than the tangent of the angle?
A
Then the object will not move on the slope
23
Q
What happens if the tangent is bigger than the coefficient
A
Then the object will move
24
Q
What happens to an object and surface when the object hits a fixed surface (table, wall)
A
Both are compressed slightly
25
Why does a ball rebound from a surface
Because both the ball and surface want to restore themselves to their original shape before the object hit the surface
26
Define elasticity
The tendency for an object to return to its original shape
27
How is elasticity calculated
Original shape/final shape
28
How do you calculate the elasticity of a ball when dropping on a fixed horizontal surface?
Height bounced / height dropped times power of 0.5
29
What can also change the amount an object will bounce?
Temperature
30
Give the two kinds of direct impact and give examples
1. When objects move towards each other in a straight lime (goal keeper punching away a shot at goal)
2. When one body is static and the other is moving towards it at right angles to the surface (dropping a ball vertically onto a level surface)
31
Describe oblique impacts and give an example
When the objects do not collide head on, but collide at an angle (bounce pass in netball)
32
What is the angle of incidence (in relation to a ball)
The angle at which an object hits the floor.
33
What is the angle of reflection (in relation to a ball)
The angle that the ball bounces back up.
34
What does the average force experienced in motion depend on?
The time over which the motion is changed
35
How can you reduce the force associated with impacts
Spread the force over a longer time
36
Give an example where you can use equipment to reduce the risk of injury and increase time of force impact
Large leg pads on a hockey goal keeper- this slows down the force and protects the skeleton. it also spreads the force over a larger area so there is less pressure on just one area
37
How much force do you experience when running?
Every time you hit the ground the force is 3 times your body weight
38
Define projectile motion
The motion of objects under the influence of gravity and air resistance
39
What happens to the horizontal/vertical component if there is no air resistance?
Horizontal component is constant, only changes to vertical component
40
Name the 3 factors that influence the distance/range objects travel
1. Speed of release
2. Height of release
3. Angle of release
41
In terms of speed and height of release, how can you increase the distance an object travels
The higher the release- further it will travel
| the faster the release- the further it will travel
42
Are horizontal and vertical components, independent or dependant on each other? explain why
They are independent of each other- you can measure separately
43
If you dropped a ball vertically and one horizontally, when should they hit the ground?
At the same time
44
Give the three ways objects can land depending on how they were released- give examples
1. Land at same height they took off- triple jump, kicking a football, hitting a golf ball
2. Land lower than the height they took off- a swimming start
3. Land higher than the height they took off- high jump, pole vault
45
What is the optimal angle or release when the release height is the same as the landing height?
45 degrees
46
When the object lands at a lower height than what it is released at, what is the optimal angle?
Less than 45 degrees.
47
When an object lands higher than where it was released, what is the optimal angle of release? -
More than 45 degrees
48
Why don't long jumpers take off at 45 degrees even those this is optimal
When travelling at your fastest possible speed it is impossible to also take off at 45 degrees- it is better to get your speed than angle
49
Except distance, what other sporting goals can you have
1. Maximimsed air time
2. Minimised air time
3. Optimise trajectory characteristics
4. Optimising trade off
50
Why would you want to maximise air time?
In sports like tennis, squash and badminton - particularly in a defensive situation, it will be easier for you to get to the object.
51
Why would you want to minimise air time?
In sports like cricket and invasion games - particularly in an offensive situation, you could create something not expected.
52
Why would you want to optimise trajectory characteristics?
In sports like netball, you look for accuracy
53
Why would you want to optimise trade-off?
Speed vs angle of release in long jump. One must be sacrificed because of another.
54
Describe drag
Drag reduces the speed of an object and slows it down. this is because it works in the direction of air flow- opposes movement
55
Describe lift
Lift helps objects stay in the air for longer by working underneath the object to push it up.
56
What angle does lift work at
Lift works at right angles to drag
57
Who might use lift?
Throwers like discus or javelin as lift will help the object to stay in the air for longer and so it will travel further
58
What is angular displacement
Angle between the start and finish point (measured in degrees or radians)
59
What is angular velocity
A change in angular displacement / time (degrees/radians per second)
60
What is angular displacement
A change in angular velocity / time (degrees/radians per second squared )
61
Where can angles be found?
Between two lines, planes or where a line and plane meet
62
When the line or plane is fixed then the angle is called...
An absolute angle
63
What is a relative angle
When the line or plane can move
64
Why are most joints relative angles?
Because they can move around
65
Is angular distance scalar or vector
Scalar
66
Is angular displacement scalar or vector
Vector
67
Is clockwise displacement considered positive or negative?
Negative
68
Is anti-clockwise displacement considered positive or negative?
Positive
69
What is a concentric force?
When the line of action passes through the centre of gravity- means there can be change in linear motion but not angular
70
What is an eccentric force
When the line of action does not pass through the centre of gravity- allows for angular and linear motion
71
Define torque
The turning effect produced by a force
72
What is torque otherwise known as
Moment of force
73
How do you calculate toruq
Torque = force x perpendicular distance from the centre of gravity and the axis of rotation
74
What is force and distance measured in?
Force is measured in newtons, distance is measured in metres
75
What is the perpendicular distance sometimes known as?
Moment arm
76
What direction of turning would make torque positive or negative
Clockwise- negative torque
| Anti-clockwise- positive torque
77
How can you increase torque?
1. Increase force
2. Increase perpendicular distance
3. Increase both
78
Why is a door handle at the opposite side to the hinge
Increases the perpendicular distance, making the torque greater and so it is easier to over come resistance and easier for you to push
79
What could you do to make it easer when working with a wretch?
You could increase the size of a wretch when your turning it to make it easier and you could put your hand further along the wretch, so it is further away from the bolt (increasing distance).
80
In what direction is the greatest force produced?
Perpendicular direction
81
Why is a sideways force less effective
Because the moment arm/distance is smaller
82
What does the amount of torque depend on?
1. The maximum force a muscle can produce
2. Where the tendon is inserted into the bone
3. The amount of force you need to overcome the resistance
83
At what angle does the greatest amount of torque come?
90 degree angle
84
How could you make a sit up harder?
1. Rasise your arms above your head to increase the distance to the axis of rotation
2. Give someone a weight to hold about their head as they do the sit up
85
How could you make a pullover harder?
Do a straight arm pullover- because when your arms are bent there is a smaller torque
86
How could you make a leg press harder?
Put your legs further down to increase the distance to axis of rotation- increasing torque
87
Where in the body is there larger torques
At stronger and larger muscles (like your hips)
88
Where in the body do we have smaller torques
Around your knees
89
The wider your hips and the further forward your knees in a squat the _____ torque
Bigger
90
What is the effect of having tendons close to the joints?
To create a larger linear distance you need to make very small angular dustances
91
Why does a sequence of rotations lead to the most effective outcome?
Because segmental sequenced rotations can generate a higher linear velocity
92
What 2 things does linear velocity depend on?
1. Angular velocity of the segment (how quickly rotating)
| 2. The distance from the axis of rotation (further away from the axis, the larger the velocity)
93
Give three advantages a golf player might have
1. Might be taller
2. Might have longer arms
3. Might have a longer club-all increasing the distance from the axis of rotation- so a bigger torque
94
What is moment of inertia?
The resistance of a body or object to changes in its angular motion
95
If an object has a greater mass, will it have more or less inertia?
More inertia
96
Besides mass, what also effects the moment of inertia?
The distance from the axis of rotation
97
What is the formula for inertia
Mass x distance from the axis of rotation
98
are heavier or lighter racquets harder to start/stop moving
Heavier racquets
99
Is it harder to create rotation when the mass is far away or close to the axis of rotation
Far away- easier to create rotation when the mass is close to the axis of rotation
100
How could you make equipment easier to rotate?
Make it smaller
101
What is the best way to run for recovery
Flex your knees more so your foot comes up to your hip when your running. if you flex your knees more then you have a greater mass closer to the axis of rotation (your hips). This makes recovery easier
102
Define angular momentum
The quantity of angular motion a body or object has
103
How is angular momentum calculated
Angular momentum = moment of inertia x angular velocity
104
Does faster and larger objects have smaller or greater momentum
Greater momentum
105
How can angular momentum be generated in the human body
Through torque when a body rotates
106
What four things does angular momentum depend on?
1. Mass
2. Angular velocity
3. Moment of inertia
4. Distance from the axis of rotation
107
When you double mass what happens to momentum?
You double momentum
108
When you double velocity what happens to momentum?
You double momentum
109
When you double the radius what happens to momentum?
Quadruple momentum
110
Where is the radius the distance from
Radius is the distance from the axis of rotation
111
Why do you quadruple the angular momentum if you double the radius?
Because the radius in the equation is squared
112
Describe Newton's 1st Law
If no external torque is applied, angular momentum remains the same. angular velocity can be changed when you change the distance from the axis of rotation
113
Does brining your body in or out increase velocity
Bringing body parts in towards the centre increases velocity- like when doing a spin in ice skating
114
Describe Newton's 2nd Law
The rate of change to angular acceleration and momentum is proportional to the torque acting on it. The greater the torque the greater the acceleration and momentum
115
Describe Newton's 3rd Law
For every torque that is exerted don the body there is an equal and opposite torque applied by the object/body onto the first object/body
116
Give an example of the transfer of angular motion
Long Jump:
- when you take off your centre of mass is forward from your point of contact (your feet)- so you are leaning forward
- your arms and legs take some of the rotation from your trunk so your trunk can remain straight and still
- as you land you bring your legs up and your trunk goes down- this is an example of action and reaction as one goes up the other comes down
117
What is the equation for angular impulse?
Torque x time
118
What can angular impulse be seen as
The area under the torque time graph
119
What does angular impulse show a change in?
Angular momentum
