Biomechanics Flashcards
What things affect how levers work
Length of lever, inertia of lever, amount of force applied
What’s newtons 1st law
(Inertia) An object will remain at a constant velocity unless acted upon by an external, unbalanced force
What’s newtons 2nd Law
(Acceleration) acceleration is directly proportional to the force applied and inversely proportional to the objects mass. F=ma, a= F/m
What’s newtons 3rd law
Every action has an equal and opposite reaction
What is the force motion principle
If force is applied to an object, motion will occur
What’s friction
The resistance that objects encounter when moving over another
What’s static friction
Force keeping objects at rest
What’s kinetic friction
Force that opposes movements
What’s inertia
An objects resistance to a change in its motion. Greater inertia = more force required to change its state of motion
What’s momentum
The quantity of motion of a moving body
P=mv
What’s impulse
change of momentum
I=Ft
What’s the impulse-momentum relationship
the impulse applied to an object will be directly proportional to the change in its momentum
What’s the law of conservation of momentum
The total momentum of two colliding objects will remain the same after the collision.
What are the types of collision
Perfectly elastic - all ‘p’ is conserved
Imperfectly elastic - some p lost
Perfectly inelastic - all p is lost
What’s coefficient of restitution
A measure of elasticity between two objects. 0-1 where 0 is perfectly inelastic collision and 1 is perfectly elastic
Example of perfectly elastic collision
Ball bouncing back to the exact drop height
Perfectly inelastic
Ball is dropped but there is no rebound
Imperfectly elastic collision
Ball bouncing lower than drop height
How to work out COR:
FV of one object - FV of other ➗ IV of other - IV of one object
Things that affect coefficient of restitution
- equipment & materials
- temp of materials (^temp=^COR)
- velocity of collision (^v = decrease COR)
What’s a concentric force
A force applied directly through an objects centre of mass, resulting in translation
Example of concentric force
Pushing the puck in ice hockey
What’s Eccentric force
Force applied to an object offset from its centre of mass resulting in translation and rotation
Example of eccentric force
- Tipping a waterbottle over by pushing the top
- tackle in AFL
What’s a force couple
When two equal but oppositely directed forces act on opposite sides of an axis of rotation at an equal radius, resulting in rotation of the object in a fixed position
What’s an example of a force couple
- bike pedals to move around
- steering wheel
What is Torque
A rotational force, resulting in angular motion
- T = F x radius (from axis)
What is a moment arm
The distance from force application to the axis of rotation
What happens when you change the length of the moment arm
Increase moment arm creates more torque but with the same amount of force exerted and vice versa
How to create more torque
Increase force and/or radius
T = Fr
What’s angular motion
The motion of an object about a relatively fixed axis
What’s angular velocity
(w) - rate of change in angular displacement
What’s angular acceleration
(a) rate of change in angular velocity over time
What’s moment of inertia
And objects resistance to a change in its angular motion. Dependent on distribution of mass and mass itself
moi = mass x radius of rotation^2
Inertia is related to radius
What’s angular momentum
(L) the quantity of angular motion possessed by a rotating body
L = moi x w
What’s a mechanical advantage (lever)
Force arm longer than resistance arm
What’s a speed advantage
Resistance arm longer than force arm
What’s a first class lever
(RAF)
- the further force is applied from the axis, the less force is needed to lift the resistance
- C1 vertebrae
Second class lever
ARF
- longer force arm than resistance arm (mechanical advantage)
- standing on tip toes
Third class lever
AFR
- force arm shorter than resistance arm (speed advantage)
- arm
What is Bernoulli’s principle
Increased velocity of fluid results in a decrease in pressure
What is lift
The force that a fluid imparts on an object as it flows over it, that is perpendicular to the oncoming flow direction
How is lift created
Fluid flowing over top of an object has to flow faster than fluid flowing over the bottom to reach the end at the same time. Pressure difference cause by Bernoulli’s principle causes fluid flow from high pressure to low pressure (up) and causes object to have lift
What’s laminar flow
Fluid flowing in parallel layers with no disruption, at the same velocity and pressure
What’s turbulent flow
Fluid flowing with irregular fluctuations, appearing random and at different velocities and pressure.
How does flow affect boundary layer
Laminar- creates less surface drag, early separation point
Turbulent- creates more surface drag, late separation point
What’s drag
A force that acts to oppose the motion of an object through fluid
Total drag
Pressure drag + surface drag + wave drag
What’s pressure drag
Force creates via pressure difference between the front and back of an object moving through fluid
How is pressure drag created
Size of Low pressure region behind object (turbulent wake) determines size of pressure difference. Fluid flows from high to low pressure - Bernoulli’s principle - and slows down object.
^frontal cross sectional area = ^ pressure drag
What’s surface drag
Drag caused by friction between the surface and the fluid flowing over it. A rougher surface traps more fluid and creates more friction
What is wave drag
Drag created by the movement of water and generation of waves at the surface of water, occurring as a loss of energy from the creator.
How to reduce wave drag
Decrease interaction with the surface. Either increase buoyancy, Change technique or go deeper.
How can wave drag be advantageous vs disadvantaged
Adv- create waves behind, propelling forward
Disadv. - pushes water forward creating resistance
What is buoyancy
An upward force exerted by a fluid that opposes the weight of the immersed body.
Affected by: - density of body in comparison to fluid
- volume of fluid displaced
Factors affecting drag
- Size of frontal cross sectional area
- velocity and resulting pressure of object
- texture of surface
- Direction of fluid flow
- size of wake
- shape of object
- slipstreaming
- fluid viscosity
Environmental factors affecting drag
- altitude - ⬆️ altitude = ⬇️drag
- humidity- ⬆️humidity = ⬇️drag
- temperature - ⬆️temp of fluid = ⬇️ viscosity = ⬇️ drag
What’s the Magnus effect
The way an objects path through fluid is changed due to spin, occurring perpendicular to fluid flow through the axis of rotation
How does spin affect flight paths
Backspin- stays in the air longer
Topspin- stays in the air less
Sidespin - travels side to side
What’s not Magnus
Anything that doesn’t spin
Eg. Swing (cricket), knuckleball, float serve
Top spin rebound
Moves fast, kicks on, travels further after bounce
Back spin rebound
Bounces high, slows down, travels less distance after bounce
What’s buoyancy affected by
- Density of body in comparison to fluid
- volume of fluid displaced
