Biomechanics

Question 1

Define linear motion.

Give a sporting example.

Answer 1

Movement of a body in a straight or curved line, where all parts move the same distance, in the same direction over the same time.
When a skier is tucked up and travelling down a slope.
Skeleton bob at top speed.

Question 2

Wheat does linear motion result from?

Answer 2

Linear motion results from a direct force being applied to a body, where the force is applied directly to the centre of a body’s mass.

Question 3

Define and give the units of:

• -> Distance
• -> Displacement
• -> Speed
• -> Velocity
• -> Acceleration

Answer 3

• -> Distance: total length of a path covered (m)
• -> Displacement: shortest straight-line route (m)
• -> Speed: rate of change in distance (m/s)
• -> Velocity: rate of change in displacement (m/s)
• -> Acceleration: rate of change in velocity (m/s/s)

Question 4

Give the equations for:

• -> Speed
• -> Velocity
• -> Acceleration/deceleration

Answer 4

–> Speed: Distance / Time taken
–> Velocity: Displacement / Time taken
–> Acceleration/deceleration:
(V2-V1) / Time taken
OR
(final velocity - initial velocity) / Time taken

Question 5

What 3 graphs can can be used to plot linear motion.

Answer 5

Distance/time
Speed/time
Velocity/time

Question 6

What does a distance/time graph show?

Why can it never go down?

Answer 6

Shows the distance travelled by a body over a period of time.
The gradient of the curve indicates the speed of the body at a certain point.
It can show when a body is at:
--> Rest
--> Travelling at a constant speed
--> Accelerating
--> Decelerating
Speed can be calculated from the graph
Speed = distance / time

The graph can never go down as distance will only ever increase.

Question 7

What does a speed/time graph show?

Answer 7

Shows the speed of a body over a period of time.
The gradient of the curve indicates the acceleration of the body at a particular point.
It can show when a body is at:
–> Rest
–> Travelling at a constant speed
–> Accelerating
–> Decelerating
Distance can be calculated as the area under the curve is equal to distance travelled.

Question 8

What does a velocity/time graph show?

Why does the curve dip below the x axis.

Answer 8

Shows the velocity of a body over a period of time.
The gradient of the curve indicates the acceleration of the body at a particular point.
It can show when a body is at:
–> Rest
–> Travelling at uniformed velocity
–> Accelerating
–> Decelerating

When it goes below the x axis it shows acceleration and deceleration in the opposite direction. E.g, when kicking a football back to your partner.

Question 9

Define angular motion.

Give a sporting example.

Answer 9

Movement of a body or part of a body in a circular path about an axis of rotation.
Arm rotating about the shoulder joint of a tennis player serving.

Question 10

What does angular motion result from?

Answer 10

Angular motion results from an eccentric force being applied to a body, where the force is outside the centre of a body’s mass.

Question 11

What is another name for an eccentric force?

Answer 11

An eccentric force is also known as torque - a turning or rotational force.

Question 12

What is a principal axis of rotation?

Answer 12

An imaginary line that passes through the centre of mass, about which a body rotates.

Question 13

What are the 3 principal axes of rotation?

Give a sporting example for each.

Answer 13

Longitudinal axis: runs head to toe through centre of mass.
Ice skater performing a spin
Transverse axis: runs from left to right through the centre of mass.
Gymnast performing a somersault.
Frontal axis: runs from front to back through the centre of mass.
Gymnast performing a cartwheel.

Question 14

What are the 3 key descriptors to angular motion?

Answer 14

1. Angular velocity
2. Moment of inertia
3. Angular momentum

Question 15

What is angular motion measured in?

Answer 15

Angular motion is measured in radians. A radian is a unit of measurement of the angle through which a body rotates.
1 radian = 57.3 degrees

Question 16

Define angular velocity.

Give the equations and units.

Answer 16

Angular velocity is the rate of change in angular displacement.
Angular velocity = angular displacement / time taken
Measured in radians per second (rad/s)

Question 17

Define moment of inertia.

Give the equation and units.

Answer 17

The resistance of a body to change its state of angular motion or rotation.
MI = sum of (mass x distribution of mass from the axis of
rotation^2)
Measured in kgm^2

Question 18

What 2 factors affect moment of inertia?

Answer 18

1. Mass
   The greater the mass of a body, the greater the moment of inertia.
2. Distribution of mass from the axis of rotation
   The further the mass from the axis of rotation, the greater the moment of inertia.

Question 19

Define angular momentum.

Give the equation and units.

Answer 19

Angular momentum is the quantity of angular motion possessed by a body.
Angular momentum = Moment of inertia x angular velocity.
Measured in kgm^2rad/s
(kilogram metres squared radians per second)

Question 20

What is the conservation of angular momentum?

Answer 20

Angular momentum is a conserved quantity that remains constant, unless an external force or torque is applied.

Question 21

What is angular analogue of Newton’s first law of motion?`

Answer 21

This is the rotational equivalent of Newton’s first law, and states:
“A rotating body will continue to turn about its axis or rotation with constant angular momentum unless acted upon by an eccentric force or external torque”.

Question 22

Define Air Resistance

Answer 22

Force that acts on a body travelling at high velocity through the AIR.

Question 23

Define Drag

Answer 23

Force that acts on a body travelling through WATER.

Question 24

What 4 factors affect Air resistance/ Drag?

Answer 24

1. Velocity
2. Frontal cross-sectional size
3. Streamlining
4. Surface characteristics

Question 25

What does fluid friction mean?

Answer 25

Fluid friction is another word for drag.

Question 26

How can athletes reduce air resistance/drag?

Answer 26

Velocity cannot be reduced to minimise AR or Drag, so other factors must be considered. Athletes such as skiers and cyclists tuck in to reduce frontal cross-sectional size and so reduce no of particles of air they hit per second. Using a streamlined position creates smooth air flow around a body. Many sports use aerofoil shapes, such as cyclists helmets or downhill skiers. The smoother the surface the lower the AR or drag. Creating smooth surfaces reduce friction between the fluid and body surface. Athletes wear Lycra clothing, shave their bodies and wax their skis to reduce friction.

Question 27

Define projectile motion.

Answer 27

Movement of a body through the air following a curved flight path under the force of gravity.

Question 28

Define projectile.

Answer 28

A body that is launched into the air losing contact with the ground surface.

Question 29

What 4 factors affect the horizontal distance travelled by a projectile?

Answer 29

1. Speed of release 2. Angle of release 3. Height of release 4. Aerodynamic factors (Bernoulli and Magnus)

Question 30

How does speed of release affect the horizontal distance a projectile travels?

Answer 30

Due to Newtons second Law of acceleration, the greater the force applied to the projectile, the greater the change in momentum and therefore acceleration of the projectile into the air.

Question 31

How does angle of release affect the horizontal distance a projectile travels?

Answer 31

45 degrees is the optimal angle to maximise horizontal distance.

Question 32

How does height of release affect the horizontal distance a projectile travels?

Answer 32

45 degrees is the optimal angle of release if the release height and landing height are equal Where the release height is greater than the landing height, the optimal angle is less than 45 degrees. Example = javelin or shot put Where the release height is less than the landing height, the optimal angle is more than 45 degrees. Example = bunker shot in golf.

Question 33

What does "parabola" mean?

Answer 33

The true flight path of a projectile unaffected by air resistance. Symmetrical about its highest point.

Question 34

When does a non-parabolic flight path occur? | Give 2 sporting examples.

Answer 34

If air resistance is the dominant force and weight is very small. 2 forces are unbalanced. E.G = Shuttle and discus.

Question 35

What is a parallelogram of forces?

Answer 35

A parallelogram illustrating the theory that a diagonal drawn from the point where forces are represented in size and direction shows the resultant force acting.

Question 36

How do you show the lift force?

Answer 36

Draw a parallelogram with weight-lift.

Question 37

How is lift formed?

Answer 37

HIgh velocity over a curved surface produces a low-pressure zone. Lower velocity below the surface creates a high-pressure zone. Air moves from high pressure to low pressure, a pressure gradient forms, creating an additional lift force.

Question 38

What is the angle of attack?

Answer 38

The most favourable angle of release for a projectile to optimise lift force due to Bernoulli principle. Using the example of a discus, it becomes a projectile when launched at an optimal angle of attack of 17 degrees, to act as an aerofoil to maximise Bernoullis lift force in flight.

Question 39

What 3 diagrams should be drawn to show the effects of Bernoullis lift force on the flight of a discus?

Answer 39

1. Free body diagram to show all 3 forces (lift, weight and air resistance). Must also include DOM. 2. Resultant force diagram to show the sum of all forces, using a parallelogram of forces (include W-lift) 3. Flight path to show the effect on the horizontal distance travelled by the discus.