Biomechanics + Kinesiology Flashcards
What do the terms kinematic and kinetics refer not?
Kinematics = motion of bodies without considering the forces that caused the motion
Kinetics = relationship between motion and its causes
What does translation and rotation mean?
Translation = a motion that moves all points of a body in a straight line, the same direction
Rotation = change in orientation of a body or segment
Define scalar, vector + magnitude
Scaler = magnitude (single number) e.g. distance, speed, time
Vector = magnitude + direction e.g. displacement, velocity, acceleration
Magnitude = Pythagoras theorem (square root of x2+y2)
What is the equation for velocity and acceleration?
Velocity = displacement / change in time
Acceleration = change in velocity / change in time
- gravity is always -9.81 m/s2
What do the letters in SUVAT stand for?
S = displacement
U = initial velocity
V = final velocity
A = acceleration
T = time
What are the 4 key SUVAT equations?
S = ut + 1/2at2
S = 1/2 (u+v)t
V = u + at
V2 = u2 + 2a
What does inertia mean?
Reluctance of a body to change its state of motion
What is the equation for linear momentum?
Linear momentum (kg ms-1) = mass x velocity
What is force?
The pushing or pulling action that an object exerts on another
- a force of 1N is the force that will produce an acceleration of 1 ms-2 in a 1kg mass
What are the internal and external forces causing translational movement?
Internal - muscle forces, joint forces
External - gravity, ground, air drag
Explain Newtons First Law
An object remains at rest or continues to move with a constant momentum unless acted upon by a net force
Explain Newtons Second Law
Rate of change of momentum of a body is proportional to the force causing it and the change takes place in the direction in which the force acts
- F = ma
Explain Newtons Third Law
Every action force has an equal and opposite reaction force
What is the equation linking to friction?
Ff = uN
Ff = limiting friction force
u = coefficient of friction
N = normal reaction force
What does centre of mass mean and the effects of…
- push through CoM
- Push outside CoM
CoM = conceptual point where all mass of a body can be considered to be concentrated
- push through CoM = only linear movement
- push outside CoM = rotational movement
What is the centre of gravity of a body?
Talking about weight rather than mass
- distribution of weight is equal in all directions
How can CoG/ CoM be found for…
- geometric shapes
- rigid bodies
- Geometric shapes = calculated as we know distribution of all points making it up
- Rigid bodies = balance or knife edge method can be used
What does equilibrium mean?
A balanced set of forces and moments resulting in no acceleration of the body
When a system is in equilibrium…. [2]
- sum of forces on body are 0
- sum of moments about a point are 0
What does moment/ torque mean and what is the equation?
Moment / torque is the product of a force and the perpendicular distance from the line of action of the force to the pivot joint
Moment (Nm) = force (N) x perpendicular distance (m)
Torque = moment of inertia x angular acceleration
What 2 pieces of equipment can be used to determine CoG?
- Statograph = a device for finding CoG by summing moments about one axis
- Reaction board = by summing moments about two axis
What does balance and stability mean?
Balance = ability to control equilibrium (state of 0 acceleration)
- CoG over base of support
Stability = tendency of a body to remain in or return to its initial position following application of a force
What does passive stability depend on?
- weight
- area of a base
- horizontal distance from CoG to pivot point
- height of CoG above base of support
What are the 3 kinds of equilibrium?
Stable equilibrium
Unstable equilibrium
Neutral equilibrium
Explain stable equilibrium
Potential energy is at a minimum
Work must be done to change
Tendency to turn to original posture
Explain unstable equilibrium
Potential energy at it near a maximum
Very little if any work must be done to change
Small movement takes the gravity line outside the base
Explain neutral equilibrium
Object moves but no change in potential energy
Base of support is small, but doesn’t matter
List some modifiable factors to increase stability
- keeping CoG over base of support
- lowering CoG
- increase mass
- extend base of support towards oncoming force
- shift CoG towards oncoming force
What are some common reflex balance mechanisms?
- ankle strategy
- hip strategy
- stepping response
- arm circle
How is impulse calculated?
Impulse = force x time
BUT
As Force = mass x acceleration
It is also = m (v-u) / t
So Ft = mv - mu
(Impulse is change in momentum)
How is the area of a trapezium calculated - IMPULSE GRAPHS?
(H1 + H2) / 2
Where H = height
What are the effects on momentum and velocity when impulse is 0?
If +ive impulse = -ive impulse
- change in momentum = 0
- change in velocity = 0
What are the effects on momentum and velocity when impulse is positive?
If +ive impulse > -ive impulse
- change in momentum > 0
- change in velocity > 0
What is energy?
Quantitative property that must be transferred to a body or physical system to perform work on a body
- one joule is the energy required to accelerate 1kg of mass at 1m/s2 through a distance of 1m
What are the 2 subcategories of mechanical energy?
Potential energy
Kinetic energy
What is potential energy?
The energy that a body possesses due to its position relative to the earths surface
PE = mass x gravity x height
What is kinetic energy?
The energy that a body possesses due to its movement
KE = 1/2 mass x velocity2
What is projectile motion?
How a point or body moves when airborne
Describe a parabola flight path
- the lines (time intervals) are the same distance apart horizontally
- but the vertical lines become closer due to gravity speeding the body up
What are the factors affecting projectile range?
- Release speed
- Release angle
- 45 degrees is optimal angle if landing height is same as release height - Release height
What is tangential release?
If a body is moving in a circle and is released, the release angle equals the tangent to the circle
What is angular displacement + what is it measured in?
It is the change in angular position
- degrees (360)
- revolutions (1 rev)
- radians (2 pi)
What’s the conversion between…
1. Degrees to revs
2. Degrees to radians
- Divide by 360
- Divide by 360 and then x by 2pi
What is angular velocity and what is it measured in?
Angular displacement / change in time
- degrees per second
- revolutions per second
- radians per second
What is angular acceleration + what is it measured in?
Change in angular velocity/ change in time
- degrees per second (squared)
- revolutions per second (squared)
- radians per second (squared)
What is circular motion + how is it calculated?
Com rotates at a constant distance from a fixed axis of rotation
Angle = arc of segment / radius of circle
Therefore…
Arc of segment = radius of circle x angle
How is tangential velocity calculated?
Linear velocity = radius x angular velocity
How is tangential acceleration calculated?
Radius x angular acceleration
How is radial acceleration calculated?
Radial velocity = 0
Radial acceleration =
1. Tangential velocity2 / radius
2. Angular Velocity2 x radius
We know that F = ma, however what is the other equation with the new equation for radial acceleration?
Force = mass x (v2 / r)
What’s the difference between linear and angular motion?
Linear = a body will remain at rest or continue in a state of constant linear motion unless it is acted upon by an external force
Angular = a body will remain at rest or continue in a state of constant angular motion unless it is acted upon by an external torque
What is angular momentum + how is it calculated?
How is linear momentum calculated?
The measure of the quantity of rotation
= moment of inertia x angular velocity
Linear momentum = mass x velocity
What is moment of inertia?
How is it calculated for a point mass and a real mass?
It is the rotational equivalent to mass - the resistance of a body to change its state of angular motion
Point mass = mass x distance2
Real mass = sum of (mass x distance2)
Is angular momentum constant in flight?
YES
Inertia (straight) x angular velocity (straight) = inertia (tucked) x angular velocity (tucked)
How can angular momentum be referenced to Newton’s second law?
The rate of change of angular momentum of a body is proportional to the torque causing it and takes place only in the direction in which the torque acts
How is torque calculated (rotational)?
Torque = moment of inertia x angular acceleration
OR
Force x distance
How is rotational energy calculated?
Rotational energy = 1/2 angular momentum x angular velocity
How is the release window for timing of release calculated?
T1 - T0
T1 = last time you can release successfully
T0 = first time can release successfully
- the greater the window, the easier the release to time is
How can a twist be produced?
Uses newtons 3rd law = for every action force there is an equal and opposite reaction force
Contact twist
- in contact with the floor so when you push off, you spin in opposite direction
Aerial twist
- the use of folding + hula motion can initiate twist after takeoff
How can tilt be produced?
By using asymmetrical limbs…
- bringing one arm down midair = tilt in opposite direction (towards that arm)
- also therefore used to correct instability (motor control)
