Biomechanics

Question 1

Define Linear Motion

Answer 1

When a body moves in a straight line or curve with all body parts moving at the same time, velocity and in the same direction

Question 2

Define Distance

Answer 2

Total path travelled
Measured in meters

Question 3

Define Displacement

Answer 3

Overall change in position of the object / the quickest route from A to B
Has both magnitude and direction

Question 4

Distance vs Displacement example

Answer 4

London Marathon
Distance - 42,000m
Displacement - 10,000m

Question 5

Speed equation

Answer 5

Speed = distance / time (ms-1)

Question 6

Define speed

Answer 6

The rate of motion of a body over time

Question 7

Define Velocity

Answer 7

The rate of motion in a particular direction over time

Question 8

Velocity equation and units

Answer 8

velocity = displacement/ time (ms)

Question 9

Define acceleration

Answer 9

The rate at which an object changes its speed or velocity

Question 10

Acceleration equation

Answer 10

Acceleration = Final - Initial Velocity
—————————— (ms-2)
Time

Question 11

Newton’s first law

Answer 11

Law of Inertia
A body continues in its state of rest or motion in a straight line unless acted upon by an external force

Question 12

Newtons Second Law

Answer 12

Law of Acceleration
The rate of change of momentum is directly proportional to the force causing it and the change takes place in the direction in which the force acts
Force = Mass x acceleration

Question 13

Newtons Third Law

Answer 13

Law of Reaction
For every action, there is an equal and opposite reaction

Question 14

Give examples of all 3 laws using a tennis serve

Answer 14

1st =The ball will rest in the players hand until tossed into the air
2nd = The ball will travel in the direction set by the contact of the players racket. Determined by strength
3rd = Foot applies force to the ground, the ground applies an equal and opposite force on the foot. Force / weight of ground is greater than the weight of the foot

Question 15

Define momentum

Answer 15

The quantity of motion possessed by the body
- Only moving objects have momentum

Question 16

Momentum equation

Answer 16

Momentum = Velocity x Mass

Question 17

Why is momentum especially important in contact sport?

Answer 17

The resulting impact depends on the momentum of the colliding bodies prior to contact
Larger mass + larger velocity = larger momentum

Question 18

Define Impulse

Answer 18

A measure of the force applied over a specific time
- used to speed things up or slow things down

Question 19

Impulse equation

Answer 19

Impulse = force x time

Question 20

Define stability

Answer 20

The capacity of an object to return to equilibrium or to its original position after being displaced

Question 21

What factors affect stability?

Answer 21

1) Base of Support = should be large and a greater number of points of contact
2) Centre of Mass = Should be low and more central within the base of support
3) Friction
4) Mass = heavier the object, more stable
5) Height = The shorter the object more stable

Question 22

What gives low vs high stability ?

Answer 22

High =
- Large base of support
- Low centre of mass
- Large body mass
- High friction at ground interface

Low =
- Small base of support
- High centre of mass
- Small body mass
- Low friction at ground interface

Question 23

What is scalars and vectors?

Answer 23

Scalars = a quantity that only has magnitude e.g mass height and speed
(Whichever direction your height is you will still always be the same length )

Vectors = A quantity that has both magnitude and direction e.g force and velocity
( A force is always described by how big it is and the direction that it is acting in )

Question 24

Define projectile

Answer 24

Bodies launched into the air that are subject only to forces of gravity and air resistance

Question 25

What factors determine the trajectory of a simple projectile ?

Answer 25

1) Speed = greater the speed the further it will travel. However important to remember the difference between vertical and horizontal speed. 2) Angle = The angle of release determines the shape of the trajectory 3) Height = Increasing the height of release improves horizontal trajectory that objects can be projected

Question 26

Describe the different flight paths

Answer 26

Parabolic ( Symmetrical Flight Path) Non-parabolic ( Asymmetrical Flight Path)

Question 27

When do deviations in the flight path occur?

Answer 27

- Objects are travelling at high speeds (golf ball) - Objects have large cross sectional area ( football ) - Objects that do not have a smooth surface (Shuttlecock)

Question 28

What is Bernoulli’s principle?

Answer 28

Describes the relationship between pressure and velocity of a moving fluid as the velocity of a fluid flow increases, the pressure exerted by that fluid decreases

Question 29

What is the correlation between velocity and pressure ?

Answer 29

They are indirectly proportional High velocity = low pressure Low velocity = high pressure

Question 30

How does an aerofoil shape allow lift?

Answer 30

Air moves faster over the top of the curved surface as it has a longer distance to travel. Creating low pressure Therefore air moves slower underneath, on the flat surface creating high pressure The pressure gradient and the low pressure on top causing lift

Question 31

How does a ski jumper create lift?

Answer 31

Create a pressure gradient The curved helmet and upper body means there is a high velocity of air travelling at low pressures The flat skis have low velocity therefore high pressure According to Bernoullis Principle a lift force will be created as gas travels from a high to low pressure, lifting the skier up

Question 32

How is downforce / negative lift produced?

Answer 32

An aerofoil shape is reversed. The curved shape of the bottom means air travels faster and creating low pressure The flat upper surface means there is low velocity of air and a high pressure. The low pressure created underneath produces negative lift, almost ‘vacuuming ‘ the car to the road

Question 33

Example of downforce / negative lift

Answer 33

F1 Car (used to keep car on ground when going around corners)

Question 34

What is the Magnus Effect?

Answer 34

Deflection of an object from its flight path, dependent on the spin implemented upon it (When a rotating object, like a ball, curves in the air as it moves )

Question 35

What are the 4 main types of spin?

Answer 35

Top spin Back spin Clockwise spin (side spin) Anticlockwise spin (side spin)

Question 36

Explain top spin

Answer 36

- An eccentric force is applied above the centre of mass of the ball - The upper surface of the projectile is rotating against oncoming airflow, decreasing velocity of air flow and creating high pressure - The lower surface rotates with oncoming air flow - This creates the Magnus effect acting downwards - The downwards Magnus Force adds to the weight of the projectile, the effect of gravity is increased. - The projectile dips and there is less flight time as the flight path shortens - The ball accelerates off the surface

Question 37

Explain back spin

Answer 37

- Eccentric force is applied below the centre of mass of the ball - The upper surface of the projectile is rotating with oncoming airflow. This increases the velocity of air flow and lowers pressure - This creates a Magnus Effect acting upwards (all gases move on a gradient from high to low pressure) - The upwards Magnus force detracts from the weight of the projectile, the effect of gravity is decreased. - The projectile floats, so there is more flight time as the flight path lengthens - The ball decelerates off the surface

Question 38

What are the 2 classifications of drag?

Answer 38

Surface and From Drag

Question 39

Describe surface drag

Answer 39

The friction between the surface of an object and the fluid environment Swimmers decrease this by shaving body hair and wearing swimming caps

Question 40

Describe form drag

Answer 40

The impact of the fluid environment on an object. It relates to streamlining, the shape of the body effects it Cyclists decrease this by creating a slip stream for cyclists behind

Question 41

Define friction

Answer 41

A force that acts in opposition to the movement of one surface over another

Question 42

Define fluid friction

Answer 42

A force that acts in the opposite direction to the direction of motion Two types = air resistance and drag

Question 43

What are the factors affecting air resistance / drag ?

Answer 43

1) Cross sectional area = larger area, greater resistance 2) Shape = More varied, the more resistance 3) Surface type = Rougher surface, greater resistance 4) Mass = Smaller mass, experience the effects of air resistance more 5) Velocity = Increase in speed, increase in resistance

Question 44

What is the difference between Turbulent and laminar Flow ?

Answer 44

Laminar = Occurs when a fluid flows in parallel layers, with no interruption between the layers. The fluid travels smoothly Turbulent = Occurs when a fluid undergoes irregular fluctuation or mixing

Question 45

How does streamlining decrease resistance for a cyclist ?

Answer 45

- Tight skin suit and shaved legs to reduce skin friction and improve aerodynamics - Handlebars Allow cyclists to bring arms closer to the body - Light carbon fibre frame of the bike

Question 46

Describe how streamlining of a swimmer reduces resistance

Answer 46

- Arms locked at the elbow - Swimming hat - Shoulders shrugged upwards - Body completely straight - Hands flat with one on top of another