fluid mechanics

fluid mechanics is the study of forces acting upon a body travelling through air or water.

Force of air acts on a body travelling at high velocity eg cyclist

force of drag acts on a body travelling through water. eg swimmer

Air resistance and drag act in opposite direction of motion, so must be minimised to perfect technique

magnitude and drag

athletes want to put all their energy into their performance so don't want to waste any. this can be done by altering position, equipment design, clothing

4 main factors that might affect magnitude of air resistance and drag?

velocity - greater velocity = greater drag and AR. Velocity cannot be reduced so other factors must be considered.

Frontal cross section - larger the frontal cross section, the larger air resistance. skiing, cycling are largely affected as body face the oncoming air.

streamlining - more streamlined and aerodynamic, the lower air resistance. streamlining is the creating of smooth air flow around a shape. many sports will use aerofoil shape.

surface characteristics - the smoother the surface, lower AR and drag. sports may have engineered clothing to deduce friction between fluid and body surface.

  • silky ycra suits

shave legs, hands and arms to maximise smooth surface

  • tear drop helmets - cycling and skiing

fins on boots and gloves - skiier

  • adopting a low crouched position

cyclists will have shoulders forwards, a high seat position, tilt the body forwards, narrow handlebars

disc wheels

projectile motion

movement of a body through the air following a curved flight path

projectiles can be an athlete, such as a high jumper or equipment thrown

the horizontal distance of the flight path is affected by : speed of release, angle of release, height of release, aerodynamic factors

Speed of release

newtons second law - greater force applied, greater change in momentum, therefore greater acceleration.

olympic throwers will train to generate max power from their muscle mass in their arm, shoulder and chest

angle of release

based of projectile released at the same speed, at an angle of: 90degrees - accelerate up, 45 - optimal angle, greater 45 - reaches peak height too quickly, less 45 - projectile does not reach sufficient height

height of release -

45 degrees is the optimum as release height and landing height are equal. however if height of release is higher or lower than landing - optimal will change

release height above - positive release height - optimal angle of release is less 45. eg javelin

release height bellow - optimal angle more than 45 as needs to increase flight time. eg bunker in golf

projectiles in path

flight path is determined by the forces acting upon it.

if weight is the dominant force - parabolic flight path. eg shot put, high mass, low velocity, small frontal cross section, smooth surface = low air resistance

air resistance dominant force = non parabolic path - eg badminton shuttle, low mass, high velocity, uneven surface = high air resistance

free body diagrams

over the phases weight does not change.

air resistance will decrease as travelling at high velocity which will cause rapid decceleration.

eg badminton - air resistance begins bigger than the weight, AR decreases as velocity of shuttle has reduced = decceleration, AR force small as the velocity of the shuttle has slowed, weight stayed the same so will accelerate down

Parallelogram of forces

asking a broken line between weight and AR = resultant force

shows the acceleration of projectile and direction the acceleration occurs + flight path

if reluctant force is closer to weight - weight is dominant = parabolic

if resultant force is closer to AR - AR is dominant = non paraboilic

shows resultant force

lift and Bernoulli

creation of additional lift force on an object in flight resulting from his conclusion that the higher velocity, the lower surrounding pressure. the additional lift will increase the time in flight and distance covered which is good for javlin, shot put

curved upper surface allow air to travel further distance = higher velocity

flat underneath - air flows shorter distance, lower velocity

all fluids move from high - low pressure, creating additional lift - ski jumper uses this by having aerofoil shape in the air, flat skis = flat underneath and curved upper.

spin and Magnus force

spin is created by applying an external force outside COM

topspin - eccentric force above COM, backspin - below COM, sidespin hook - right COM, sidespin Slice - left COM

Topspin creates a Magnus force down, shortens flight path. additional Magnus force created by pressure gradient

backspin creates Magnus force up, lengthens flight path

Sidespin - Magnus force to right and left