Biomechanics

Question 1

On a diagram/graph showing the flight path of an object, what force changes size and which doesn’t?

Answer 1

Vertical force changes size and goes from +ive to -ive.

Horizontal force remains constant (ignoring air resistance)

Question 2

what is the optimum angle of release?

Answer 2

45 degrees

Question 3

Define the Bernoulli Principle

Answer 3

Refers to changes in fluid pressure (H20 or air) due to diff. in fluid velocity

Question 4

What does fluid flow around irregular shaped projectiles cause? Why?

Answer 4

Pressure differences

== Molecules have to travel diff. distances to pass around it.

Question 5

What shaped objects produce lift?

Answer 5

Aerofoil (wing shaped)

Question 6

Describe how air flows over aerofoil objects

Answer 6

Air travels a longer distance on top = low pressure = high velocity

Air travels shorter distance underneath = high pressure = low velocity

Question 7

What does fluid moving at high + low speed cause?

Answer 7

High speed = drop in pressure

Low speed = increase in pressure.

Question 8

What happens with the slower moving fluid + the faster moving fluid?

Answer 8

Slower moving will exert higher pressure on object than faster fluid === lift or downforce.

Question 9

Give an example of a lift in an object

Answer 9

Air moves quickly over the top of a discus that is released at an angle == so its lifted.

Question 10

What happens to a ski jumper in Bernoulli’s principle

Answer 10

Will attempt to adopt an aerofoil position to maximise lift as curve on top + flat underneath

Question 11

How are formula 1 cars designed to counteract the Bernoulli effect

Answer 11

Using ‘upside down’ aerofoils (spoilers) to ⬆️ fluid pressure above car, pushing it down onto track.

Question 12

What is the Magnus effect

Answer 12

Bernoulli Principle applied to spinning objects.

Spin is created by applying a force outside an object’s centre of mass.

Question 13

What does spin cause the projectile to do?

Answer 13

Curve away from it’s original flight path.

The side spinning in the direction of the air will result in a high velocity = low pressure causing a pressure differential.

Question 14

How is top spin created?

Answer 14

By applying a force ABOVE centre of mass.

i.e hitting tennis ball low to high + brushing over ball == forward rotation around transverse axis.

Question 15

What does top spin result in?

Answer 15

Causes a Magnus force to act on the ball in a downwards direction.

== Tennis players can then hit the ball harder but still ensure it lands in-court.

Question 16

Why do top spin strokes tend to be harder to return?

Answer 16

Magnus effect results in a higher bounce.

Question 17

How is back spin created?

Answer 17

By applying a force BELOW centre of mass.

i.e hitting a tennis ball high to low + slicing under ball == backward rotation around transverse axis.

Question 18

What does back spin result in?

Answer 18

Causes a Magnus force to act on ball in an upward direction.

Question 19

Define angular motion

Answer 19

Movement around a fixed point or axis.

Occurs when a force is applied OUTSIDE the centre of mass.

Question 20

Define angular displacement

Answer 20

Smallest change in angle between starting + finishing point, how far something has turned. (Radians)

i.e in 1 pirouette = angular displacement: 0 rads.

Question 21

Define angular velocity

Answer 21

Rate of change of angular displacement, how quickly something spins.

(rad/s)

Question 22

Define angular acceleration

Answer 22

Rate of change of angular velocity, how quickly somethings gets spinning or slows spinning.

(rad/s^2).

Question 23

Define moment of inertia

Answer 23

The resistance of a body to angular motion

kg/m^2

Question 24

What does the moment of inertia depend on

Answer 24

Mass of body

Distribution of mass around the axis - radius of gyration.

Question 25

How must an athlete increase angular velocity?

Answer 25

By bringing their mass TOWARDS the axis of rotation by changing the shape of their body, tucking in.

Question 26

What remains conserved in the graphical representation of a somersault?

Answer 26

Angular momentum

Whilst moment of inertia + angular velocity are inversely proportional to each other.

Question 27

What can fluid be a representation of in fluid mechanics?

Answer 27

Air or H20

Question 28

Define laminar flow

Answer 28

When fluid layers move parallel to each other + don’t cross.

a.k.a streamlined flow

Question 29

Define turbulent flow

Answer 29

Irregular + rough.

Characterised by small ‘whirlpool’ regions in the fluid layers.

Question 30

What happens to the fluid nearest an object when the object moves through it?

Answer 30

Slows down.

Mol. of fluid near object (boundary layer) are disturbed + move around.

Question 31

What is the behaviour of the fluid around the object dependent on?

Answer 31

Shape (front cross-section + surface)

Speed

Viscosity

Question 32

What is drag force

Answer 32

An ⬆️ in fluid resistance = resisting motion

Question 33

How can performers overcome drag forces?

Answer 33

⬇️ cross-sectional area (i.e tucking in)

Manipulate surface properties (i.e swim caps + compression clothing)

Consider ⬆️ speed vs drag

Question 34

What is the relationship between speed + drag?

Answer 34

Faster the object = greater the drag.

Question 35

How might a swimmer minimise turbulent flow

Answer 35

By analysing laminar flow + attempting to alter boundary layers

Question 36

How might an athlete decrease or increase surface friction?

Answer 36

By choice of footwear.

Question 37

How might cricketers attempt to ⬆️ turbulent flow

Answer 37

By creating more boundary layers to generate swing.

Rough surface on 1 side = asymmetrical flow/wake + ball moves in direction of turbulent flow.

Question 38

How are golf balls designed to take adv. of turbulent flow

Answer 38

Dimples create turbulence which sucks air to ball to delay separation.

In which a smaller vortex creates less drag.

Question 39

Explain, using the Bernoulli principle, how the lift force is generated

Answer 39

Air flows faster over top of discuss as it has further to travel = low pressure created.

Air flows at a slower velocity under discuss as it has shorter distance to travel = high pressure created.

=== Pressure gradient

As air moves from area of high to low pressure, lift force is generated.

Object needs to be an AEROFOIL SHAPE