Sport Biomechanics Flashcards
Angular velocity
angular velocity/ time
angular acceleration
change in angular velocity/ time
moment of inertia
mass x distance^2
angular momentum
moment of inertia x angular velocity
torque
moment of inertia x angular acceleration
angular impulse
torque x time = change in angular momentum
Kinetic Energy
1/2 x moment of inertia x angular velocity^2
arc length
radius x angle
tangential velocity
radius x angular velocity
tangential acceleration
radius x angular acceleration
radial acceleration
radius x angular velocity ^2 or v^2/r
SUVAT Equations
v= u +at v^2= u^2 +2as s= ut + 1/2 at^2 s= 1/2 (u+v) x t
Newtons 1st law
An object either is at rest or moving with constant momentum unless acted upon by an external force
Newtons 2nd law
The sum of the forces on an object is equal to the total mass of that object multiplied by the acceleration F=ma. Also rate of change of momentum is proportional to the force.
Newtons 3rd law
When one body exerts a force on a second body, the second body simultaneously exerts an equal and opposite force back
Friction
= coefficient of friction x normal reaction force
Gravity Force Equation
Force= (G x m1 xm2)/radius ^2
Moments
= force x perpendicular distance
Scaler and examples
Magnitude- mass, time, speed
Vector and examples
magnitude and direction- weight, displacement, velocity and aceleration
Define Inertia
Reluctance of a body to change its state of moment.
High inertia= difficult to move, change shape.
Large mass = large inertia
what are the 2 types of movement and define
Linear motion (translation) and angular motion (rotation) Linear motion= when the centre of mass is moving
Difference between distance and displacement
Distance is the total distance travelled whereas displacement is the shortest route from the start to the end, it’s found using Pythagoras and will have a x and y component so can be written as a vector.
What don’t we call acceleration
Deceleration- always call it positive or negative acceleration
What does a standard 50Hz mean
In video, you’re taking 50 pictures every second
Whats a high speed video
you’re taking more than 50 pictures a second
How does a Charge coupled device work
There’s a chip which has diodes on it that are light sensitive. When light comes through, it hits the photocytes and produces a small charge. Light falls all over the chip and the chip measures the amount of light that’s fallen on each pixel. Then it sends the information to the computer so we know how much light has hit the chip in total
what are the 2 ways a charge coupled device could see a coloured image
1) . Use 3 chips so when light enters the front of the camera it gets split by a prism and is aimed at 3 different chips with a filter on. Have a red, green and blue components, then when you know hoe much light s hitting each component you put it together to get a coloured image.
2) . Can use a single chip which has a different filters over light sensitive diodes on chip (known as Bayer filter). There’s more green filters because the human eye is more sensitive to green.
Field of view
Make sure the field of view contains all the action you’re interested in
Focal length
Distance from sensor at the back TO the lens at the front
By varying this it changes the filed of view, its like zooming in
what does a small or large focal length mean
small focal length means a wide field of view
large focal length means a not as wide field of view
why should u avoid autofocus
Because when u start moving it will try and refocus the camera.
can autofocus to begin with but then turn it to manual
whats shutter speed and what doenst it affect
shutter speed varys the time the sensor is exposed to light
It doesn’t affect the number of frames per second
what happens if the shutter speed isn’t optimal
If shutter is open too long then it creates a blurry image.
However if its not open long enough, then not enough light will get In so it will be a dark image.
In this case you can additional lighting to brighten the image.
Define centre of mass
a conceptual point, that can be real or fictitious, where all the mass of a body can be considered to be concentrated.
Its not a real point so you cant weigh or touch it
How does motion occur in respect to CoM
The resultant force must pass through the CoM, if the CoM isn’t on the body then the projection of where the force is acting must pass through the CoM.
Describe Gravity
Gravity is the force that acts between 2 masses. Its attractive and depends on the size of the masses and their separation
Define centre of gravity
Conceptual point which would have the same potential energy of the body and through which the resultant gravitational forces will pass
characteristics of a system being in equilibrium
sum of forces on body = 0
sum of moments about a point = 0
What does the balance method do
It uses moments to calculate the centre of gravity
Equipment for determining CoG and equation
Statograph- a device for finding the CoG by summing moments about one axis
Reaction Board- sums moments about 2 axis
total weight x total distance = (board weight x CoM of board distance) + (persons weight x CoM of persons distance)
Whats the segmental method
Take moments along a line in components and then add them together and then use this to the find the overall CoG of the whole line.
Define stability
the tendency of a body to remain or return to its initial position following the application of a force.
Stability can be passive or dynamic
what does passive stability depend on?
- weight
- area of the base
- horizontal distance of the CoG to pivot point, the greater the distance, the more effort to become stable
- height of CoG above the base
Potential energy when stable
Potential energy is at a minimum when equilibrium is stable.
Work must be done to move an object out of equilibrium and it has a tendency to return back to normal position
Potential energy when unstable
Potential energy is a or near a maximum.
Very little or any work must be done to change this, any small movement will cause it to change position and become more stable
Whats neutral equilibrium
Its an odd situation where an object moved but theres n change in the CoG position.
Works in symmetrical objects and the base of support is small
When are humans passively stable
only when theyre lying flat
how can people become more stable
use crutches/rods/guy ropes but moving around is still hard
or can use a skateboard, dynamic stability
humans need to use muscular force to remain balanced
common reflex balance mechanisms
ankle strategy
hip strategy
stepping response
arm circle
define force
a force of 1N is the force that will produce an acceleration of 1ms^-2 on a 1kg mass
Whats polar form
having an angle and a magnitude
how do u rearrange equations to show impulse = change in momentum
impulse = ft f=ma a=(v-u)/t f=m(v-u)/t ft=mv-mu
How do u find impulse on a graph
its the area under the graph, calculate it using the trapezium rule
requirements for impulse
- must know intial conditions
- apply to x,y,z directions
- must be net force
how do u measure force
use a force plate
describe how force plate works
has 4 transducers, one in each corner, these change state depending on how much force is applied to them so in each one measures the force in their corner and then the forces are summed.
gives info about the 3 planes
does air resistance matter
not in calculations
but yes in real life it does especially with lighter objects
shape of projectile motion
parabola
where/how deoes gravity act
only acts in the vertical direction, the horizontal component = 0
so by taking regular time intervals, the size of the vertical gaps will increase while horizontal gaps remain the same
what effects the range of a projectile
- release velocity, faster u throw, the further it goes
- release angle- if throwing and landing height r the same optimum angle = 45 otherwise its just less
- height og release
how do u solve a projectile problem
1) . divide into horizontal and vertical components
2) . see if u can solve for either vertical or horizontal with info given to u
3) . apply SUVAT to get unknown
4) . solve for other component and check it makes snese
tricks in projectile motion
- top of the parabola vertical velocity =o
- if ends and start same place, displacement =0
- if symmetrical then same displacement on the way up and down, can split it in half
how do u throw for max distance
use max velocity and the optimum release height and angle are dependent on a persons physical characteristics
As release height increases, optimum angle decreases
define motor control
=study of how movement is controlled
-ability to regulate or direct mechanisms essential to movement
whast the process to get a response
stimulus=processing=response
in processing theres stimulus identification- response selection- response programming
when does a somersault speed up
when it goes from the tucked to straight position
mechanical principle in rotation
-angular rotation, it must be conserved
key points of moment of inertia
- rotational equivalence to mass
- resistance of a body to change its state of angular motion
- measure distribution about an axis
- 3 axis, = lateral, longitudinal and frontal
which poritions have most inertia
straight=large inertia, smaller angular velocity
pike = middle one
tucked= small inertia, large velocity
equation for momentum in free fall
momentum is conserved
IsWs=ItWt
how can u combat roational movement to conserve angular momentum
swing arms the opposite way to the way youre rotating
easier in tucked position as inertia is smaller so esier to create movement
how can u change angular momentum
by an external force acting on it
what positions does a force acting cause rotation
wont rotate if force acts through the centre of mass
but by force being opposite to direction of rotation causes rotation
swing arms forward to stop rotating forward
whats aperture
size of the hole at the front of the camera
reffered to as f/stop number and its the ratio of focal length to aperture diameter
meaning of small and large f/stop
small f/stop= larger the hole, larger aperture, mall depth of field, small shutter speed
large f/stop= small hole, small aperture, large depth of field, large shutter speed
what do u need for 2d analysis
a camera
plane of movement
place camera perpendicular to movement plane
record scale info
scale info
put an object of known dimensions in plane of movement
digitise object
calculate scale factor(done by dividing pixels/meters)
avoid perspective and parallax error
perspective and parallax error
move camera further away to minimise persectve error
parallax error dpeneds where u place your headso reduce parallax error by placing camera perpendicular to movement
