PE - y13 biomechanics

Question 1

Linear motion

Answer 1

Movement of a body in a straight or curved line where all parts move the same direction over the same time

Creation of linear motion: Direct force is applied to the body at the centre of mass e.g., Ski Jumping/skeleton

Key descriptors:
- Distance
- Velocity
- (De) Acceleration
- Displacement
- Speed]

Question 2

Distance-time graph

Answer 2

Rest: Line does not go up or down
Constant speed: Goes up in constant diagonal line (changing)
Acceleration: Line gradually gets steeper, more distance is covered in the same amount of time
Deceleration: Curve starts to level of, less distance is covered I the same time

Question 3

Angular motion

Answer 3

Movement of a body in a circular path about its axis of rotation, more common than linear motion

Measured: Radians 360 degrees

Creation of angular motion: Eccentric force known as torque is applied to a body outside the centre of mass, caused by an external force

Question 4

Axis of rotation

Answer 4

Longitudinal: Runs from head to toe, through the centre of mass e.g.m Spin in ice skating

Transverse: Runs from left to right, through the centre of mass e.g., Somersault in gymnastics

Frontal: Runs from front to back, through the centre of mass e.g., Cartwheel in gymnastics

Question 5

Angular motion descriptors

Answer 5

Angular distance: Total angle body turns from start to finish about an axis

Angular displacement: Smallest Ange between start and finish position about an axis

Angular speed: Rate of change in angular distance = Angular distance/time taken

Angular acceleration: Rate of change in angular velocity = final - initial angular velocity/time taken

Angular velocity: Rate of change in angular displacement or he rate of rotation = angular displacement/time taken

Angular momentum: The amount of motion a body or object has during rotation (how much spin) = angular velocity x moment of inertia

Question 6

Moment of inertia

Answer 6

Resistance of a body to change its state of angular motion or rotation (the tighter the performer tucks, the faster they rotate)

Mass x distribution of the mass from their axis of rotation (squared)

Question 7

Angular momentum and Newtons first law

Answer 7

‘A rotating body will continue to turn about its axis of rotation with constant angular momentum unless acted upon by an eccentric force or external torque’

Question 8

Air resistance and drag

Answer 8

Air resistance: Acts on a body travelling at high velocity through the air

Drag: Action a body travelling through water

Question 9

Factors affecting air resistance and drag

Answer 9

Velocity: The greater the velocity, the more the air resistance or drag, velocity however cannot be reduced

Frontal cross-sectional area: The greater it is, the larger the air resistance

Streamline and shape: More aerodynamic the body, the lower the air resistance or drag

Surface: The smoother the surface, the lower the air resistance and drag

Question 10

Projectile definitions

Answer 10

Projectile: A body launched into the air and is subject to weight and air resistance

Projectile motion: Movement of a body through the air following a curved flight path under the force of gravity

Flight path: Shows the overall distance travelled after gravity has accelerated it back to the ground

Question 11

Factors affecting horizontal distance travelled

Answer 11

Speed of release: The greater the speed of release, the greater the distance

Angle of release: Optimum angle of release is 45 degrees

Height of release: Depending on whether it is positive or negative relative release, the optimum angle of release may change

Aerodynamic factors: Bernoulli principle pr aerofoil

Question 12

Flight paths

Answer 12

Parabolic: Symmetric about its highest point
- Weight doesn’t change
- Dominant force - weight

Non-parabolic: Asymmetric about its highest point
- Weight changes e.g., shuttlecock
- Dominant force - air resistance

Question 13

Bernoulli principle

Answer 13

Creation of an additional lift force and on a projectile in flight resulting from the conclusion that the higher the velocity of airflow, the lower the surrounding air pressure

Impact: Additional loft force means the projectile will hang in the air for a longer time

Applies to:
- Javelin
- Ski jumping
- Discus

Question 14

Aerofoil

Answer 14

Curved upper surface (low pressure - air faster) and flat underneath surface (high pressure - air slower). Air is forced apart and there are different velocities above and below the shape

Question 15

Airflow diagrams

Answer 15

• Air parts as it goes over the shape, moves at different velocities above and below the shape
• This impacts the pressure of airflow and a pressure gradient is formed which generates additional force
• The curved upper surface forces air flow to travel a further distance and therefore move at a higher velocity

Question 16

Resultant force

Answer 16

• Shows sum of all force acting on an object using a parallelogram
• Lift reduces and therefore so does weight
• Shows the overall effect of an aerofoil in flight
• Weight and lift both act vertically

Flight path:
- Shows effect of horizontal distance
- Shows overall effect of an aerofoil in flight

Question 17

Magnus force

Answer 17

The creation of an additional Magnus force on a spinning projectile which deviates from it’s expected flight path

Question 18

Types of spin

Answer 18

Topspin: Eccentric force above centre of mass (spins downwards around transverse axis)
Backspin: Eccentric force applied below centre of mass (spins upwards around transverse axis)
Sidespin hook: Eccentric force applied right of centre of mass (spins left around the longitudinal axis) causing it to deviate to the left
Sidespin slice: Eccentric force applied left of centre of mass (spins right around the longitudinal axis) causing it to deviate to the right

Question 19

The Magnus effect

Answer 19

• The way a projectile spins determines the direction, velocity and pressure of air flow around it
• A pressure gradient is formed either side of the spinning projectile and an additional Magnus force is created which deviates the flight path
• All forms of spin create a non-parabolic flight path