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pe > 9.3- Fluid mechanics and projectile motion > Flashcards

9.3- Fluid mechanics and projectile motion Flashcards

1
Q

What is fluid mechanics

A

study of the forces acting on a body travelling through the air/ water

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2
Q

Name the issues air resistance and drag pose against an athletes body

A

air resistance and drag act against the motion of a body
-place an increased psychological demand
-can lead to early fatigue and poor performance

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3
Q

Name the 4 main factors that affect the
magnitude of air resistance and drag on a body

A

-velocity -> greater the velocity -> greater the force of air resistance/drag opposing their motion

-frontal cross -> low crouched psotion of a downhill skier reduces air resistance & drag

-streamlining and shape -> more aerodynamic the shape of a body/ equipment -> lower the air resistance/ drag

-surface characteristics -> e.g. increased smoothness -> lycra swimsuits reduce air resistance

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4
Q

How does velocity affect magnitude of air resistance and drag

A

-greater the velocity the greater the air resistance or drag

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5
Q

Name 3 sports that are affected by air resistance and drag due to their high velocities

A

-track cycling
-speed skating
-freestyle swimming

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6
Q

How does frontal cross affect magnitude of air resistance and drag

A

larger the frontal cross, the larger the air resistance or drag

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7
Q

Name 2 sports that are affected by air resistance and drag due to their large frontal cross

A

-track cycling
-downhill skiing

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8
Q

How does streamlining and shape affect magnitude of air resistance and drag

A

more streamlined/ aerodynamic the shape of the body in motion- lower the air resistance or drag

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9
Q

What is aerofoil

A

streamlined shape with curved upper surface and flat lower surface designed to give an additional lift force to a body

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10
Q

What is streamlining

A

creating of smooth air flow around aerodynamic shape

-the more aerodynamic the shape of a body the lower the air resistance

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11
Q

How does surface charcteristics affect magnitude of air resistance and drag

A

smoother the surface the lower the air resistance and drag

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12
Q

Give examples of how downjill skiers battle air resistance to maximise performance

A

-minimise frontal cross –> low crouch position

-wear tear-drop-shape helmets –> streamlined shape

-wear super silky lycra suits –> smooth surface

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13
Q

Give examples of how track cyclists battle air resistance to maximise performance

A

-lightweight bike with aerdoynamic features –> disc wheels

-aerodynamic riding position -> shoulders forward

-aerodynamic helmets

-tight fitting lycra skin suits- smooth socks pulled over shoes

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14
Q

What is projectile motion

A

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

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15
Q

What is a projectile

A

body launched into air and subjected to weight and air resistance forces

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16
Q

Give 2 examples of the 2 types of projectiles

A

-athlete (high jumper)
-equipment thrown, hit, kicked (javelin, tennis ball)

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17
Q

What occurs when a projectile is in flight

A

projectiles follow a flight path through the air

-flight path from start - finish shows overall distance travelled

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18
Q

What graph can be used to show the flight path a projectile takes

A

graph of height against horizontal distance travelled

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19
Q

Name the 4 factors that affect the distance travelled by a projectile

A

-speed of release -> greater speed of projectile, further it will travel

-angle of release -> 45 degrees -> optimal angle to maximise horizontal distance

-height of release -> 45 degrees -> optimal angle if release height and landing height are equal
-where release height is ^ than landing height, optimal angle is less than 45 degrees

-aerodynamic factors (Bernoullli and Magnus) ->

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20
Q

How is the horizontal distance travelled by a projectile affected by the speed of release

A

(newtons 2nd law)- greater the force applied to projectile - greater the change in momentum - further projectile accelerates into air

-greater the outgoing speed of the projectile, further it will travel

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21
Q

How is the horizontal distance travlled by a projectile affected by the angle of release

A

-90 degrees- projectile will accelerate vertically upwards and come straight back down- travelling 0m

-45 degrees- optimal angle to maximise horizontal distance

-60/ 75 degrees- projectile reaches peak height too quickly- rapidly returns to ground

-30 degrees- projectile doesnt achieve sufficient height to maximise flight time

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22
Q

How is the horizontal distance travelled by a projectile affected by the height of release

A

-45 degrees -> optimal angle of release

-where release height is above landing height- optimal angle of release- less than 45 degrees as projectile already has increased flight time due to increased height of release

-where release height is below landing height- optimal angle of release is more than 45 degrees as projectile needs increased flight time to overcome obstacle

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23
Q

What is the drag

A

force that opposes the direction of motion of a body through water

24
Q

What is a projectile

A

body that is launched into the air losing contact with the ground surface, such as a discus

25
Q

one factor that affects horiozntal distance travlled by a projectile

A

-speed of release - greater speed of release- will be thrown further

-height of release

-angle of release

26
Q

What is parabolic

A

uniform curve symmetrical about its highest point

27
Q

What is a parabolic flight path and when does it occur

A

flight path symmetrical about its highest point caused by dominant force of weight on a projectile

-occurs if weight is dominant force & air resistance is small

28
Q

Give a sporting example of a parabolic flight path

A

shot put

-has high mass, travels through air at low velocity with small front cross-sectional area -> making air resistance minimal

29
Q

What is a non-parabolic flight path and when does it occur

A

a flight path asymmetrical about its highest point caused by dominant force of air resistance on a projectile

-occurs if air resistance is dominant force and weight is very small

30
Q

Give a sporting example of a non- parabolic flight path

A

badminton shuttle

-has low mass, travels at high velocities with uneven surface -> creates air resitance

31
Q

Explain the free body diagram of a badminton shuttle in the start, mid and end of flight phases

A

-start: AR is much larger than W -> as velocity of shuttle = high as it leaves racket head

-mid: size of AR force has decreased as velocity of shuttle has reduced -> size of AR force causes shuttle to decelerate

-end: AR force = small, velocity of shuttle has slowed -> W force is larger than AR -> shuttle falling vertically -> non-parabolic flight

32
Q

Name the 3 phases of motion within a flight path

A

-start of flight

-mid flight

-end of flight

33
Q

What is a parallelogram of forces

A

diagram of the object showing the forces acting on a projctile in flight

-> e.g. air resistance (direction and size)
weight (direction and size)

34
Q

Describe the 3 steps you would take to draw a parallelogram of forces

A

-draw free body diagram showing weight and air resistance

-add broken parallel lines to weight and air resitance arrows to create a parallelogram

-draw diagonal line from origin of weight and air resistance (centre of mass of projectile) to opposite corner of parallelogram with arrow labelled ‘resultant force’

35
Q

What is an aerofoil

A

streamlined shape with curved upper surface & flat lower surface

-> designed to give additional lift force to body

36
Q

What is the resultant force

A

it shows the acceleration of a projectile and the direction in which the acceleration occurs

-also shows flight path

37
Q

How do you know through looking at the resultant force if the flight path is parabolic or non-parabolic

A

parabolic -> if resultant force = closer to weight arrow -> weight = more dominant -> parabolic flight path

non-parabolic -> if resultant force = closer to air resistance -> AR = more dominant -> non-parabolic flight path

38
Q

Name characteristics of an aerofoil and how this is beneficial

A

-has a curved upper surface, forcing air flow to travel further distance -> moving at higher velocity

-has flat underneath surface -> air travelling at shorter distance at a lower velocity

-above the curved surface -> low-pressure zone is created

-below the flat underneath surface -> high-pressure zone is created

39
Q

What is Bernoullis principle in simple terms

A

higher the velocity of air flow, the lower the surrounding pressure

40
Q

How does an aerofoil shape give an additional lift force to a body according to Bernoullis principle

A

-curved upper shape -> air flow travels further -> moves higher velocity -> low pressure zones created

-flat underneath -> air travels shorter -> moves at lower velocity -> high pressure zone created

THEREFORE:
-as velocity increases, pressure decreases

-as fluids move from area of high pressure -> low pressure -> pressure gradient forms -> creating additional lift force

-lift force ^ time projectile hangs in air -> ^ flight path, horiziotal distance -> ^ results

41
Q

What is lift force

A

additional force created by pressure gradient forming on opposing surfaces of an aerofoil moving through a fluid

42
Q

What is angle of attack

A

most favourable angle of release for projectile to optimise lift force

43
Q

Give an example of a sport which adopts Bernoullis principle

A

ski jumper

44
Q

Explain using a sporting example Bernoullis downward lift force principle

A

-front wing funnels air down through narrow space underneath cars chassis

-soiler acts as an inverted aerofoil -> forces air underneath to travel further distance

-this ^ air velocity unerneath car -> creating areas of low pressure

-pressure gradient is formed; downward lift force = created

-results in ^ grip & friction around corners at high speeds

45
Q

How is spin created

A

created by applying an external force outside centre of mass

46
Q

Name the 4 types of spin, explain the force applied and the result of this force

A

topspin -> eccentric force applied above COM, projectile spins downwards around transverse axis

backspin -> eccentric force applied below COM, projectile spins upwards around transverse axis

sidespin hook -> eccentric force applied right of COM, projectile spins left around longitudinal axis

sidespin slice -> eccentric force applied left of COM, projectile spins right around longitudinal axis

47
Q

What is a magnus force

A

force created from a pressure gradient on opposing surfaces of a spinning body moving through the air

48
Q

What magnus force does topspin create and how does this effect its flightpath

A

topspin creates downward magnus force

-> shortening flight path

49
Q

What magnus force does backspin create and how does this effect its flightpath

A

backspin creates upward magnus force

-> lengthening flight path

50
Q

What magnus force does sidespin rotation create and how does this effect its flightpath

A

sidespin rotation creates magnus force to the right and left

-> swerving projectile right (slice) & left (hook)

51
Q

What is the magnus effect

A

creation of an additional magnus force on spinning projectile which deviates from the flight path

52
Q

What is a hook

A

type of sidespin used to deviate projectiles flight path to left

53
Q

What is a slice

A

type of sidespin used to deviate projectiles flight path to right

54
Q

Explain how topspin occurs in tennis

A

upper surface of ball rotates towards oncoming air flow -> oppoising motion, decreasing velocity of air flow -> creating high pressure zone

-lower surface of ball rotates in same direction as air flow, increasing velocity of air flow -> creating low pressure zone

-pressure gradient forms, additional magnus force is created downwards

-downward magnus force adds weight to projectile

-projectile dips in flight -> less time in air -> flight path shortens

55
Q

Name 3 reasons as to why spin is useful in table tennis and tennis

A

-gives ball stability in flight

-can confuse opposition

-topspin shortnes flight path -> allowing ball to still be hit hard but still land in court

56
Q

hook spin description

A
57
Q

slice spin dexciription

A

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