Biomechanics Flashcards
Mechanics
a branch of maths dealing with motion and forces producing motion.
Biomechanics
Study of mechanics in biological systems like humans.
Force=
Mass x Acceleration
Distance =
Speed x Time
Momentum=
Mass x Velocity
Pythagoras=
A squared + B squared = C squared
Velocity=
change in displacement/change in time
Speed=
Distance/Time
Mass=
Force/Acceleration
Acceleration=
Force/Mass
SOH Sine=
Opposite/Hypotenuse
CAH Cosine=
Adjacent/Hypotenuse
TOA Tan=
Opposite/Adjacent
Distance
- Distance is measured along the path of motion.
- refers to the sum of all movements in whatever direction
- 1 lap of the track = 400m
- distance is a scalar quantity.
Scalar
a simple measure of magnitude (how big, fast, long… something is)
Displacement
- Linear displacement is measured in a straight line from the initial position to the final position.
- when a runner completes a lap of the track, linear displacement is 0m.
Displacement is a vector
Vector
A vector quantity has a magnitude and direction. Displacement is 21m right for example.
Angular Distance
length of the angular path that an object travels
Angular Displacement
The angle between the final position and the initial position
Angular Speed/Velocity
Rate of change, over time, in angular distance/displacement
Angular Acceleration
Rate of change, over time, in angular velocity
Converting Radians to Degrees
Multiply by 180 and divide by Pi
Converting Degrees to Radians
Multiply by Pi and divide by 180
Converting degrees into revolutions
Divide by 360
Clockwise and Anticlockwise positive or negative
Clockwise is negative
Anticlockwise is positive
Right hand rule
What is important about our calibration object
size, shape, number of points, location in the field of view
Considerations when recording videos
Capture area, Camera set-up and Calibration
Force
- A force can be thought of as a push or pull acting on the body.
- Each force is characterised by its magnitude, direction and point of application
Examples of Force
Body Weight, Gravity, Air/Water resistance, Friction
Friction
Friction is a force acting parallel to the interface of 2 surfaces that are contacted during the motion or impeding motion of 1 surface as it moves over the other.
Newtons First Law (of inertia)
- a body will continue in its state of rest or motion in a straight line unless acted upon by external forces.
- Thus, unless a net force is exerted on an object, the object will remain stationary or move uniformly.
- This is the law of inertia
Newtons Second Law (of acceleration)
- if a ball is hit, it will travel in the direction of the line of action of the force applied and the resulting speed is dependent upon the amount of force applied.
- the 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.
- thus, if the force is constant, acceleration or deceleration will be constant
Newtons Third Law
- when one body exerts a force on a second, the second exerts a reaction force that is equal in magnitude and opposite in direction on the first body.
- for every action there is an equal and opposite reaction.
Moment of Inertia
- Moment of inertia is the inertial (tendency of a body to resist its state of motion) property for rotating bodies, that increases with both mass and the distance the mass is distributed from the axis of rotation.
How to Measure: Weight- Muscle Strength- Impact Force- Ground Reaction Force Acceleration-
Weight= Scales Muscle Strength= Dynamometer Impact Force= Load Cells Ground Reaction Force= Force Plates Acceleration= Accelerometers
Force Plates
- A force plate is an electronic device that can measure ground reaction force.
- A voltage is produced that is directly related to the amount of force applied
Accelerometers
- An accelerometer is an electronic device that can measure linear acceleration.
- A voltage is produced that is directly related to the amount of force applied.
Diverging and Converging Streamlines
Diverging Streamlines = Slowing Down
Converging Streamlines = Speeding Up
Total Drag
- Form/Profile Drag
- Skin/Surface Drag
- Wave Drag
Centre of Mass
- is the point of an object around which the mass is equally distributed.
- is the point of an object which the line of action of the weight force can be assumed to act.
- is the point of an object, gravity is considered to act through.
Location of COM
- in symmetrical, homogenous objects, the COM is at the centre (ball or solid cube)
- in objects with unequal mass distribution, COM shifts in the direction of the greater mass.
- COM doesn’t always lie within the physical constraints of the body.
- since humans are multisegmental, COM is not fixed.
COM applied to high jump
- COM is determined at take-off.
- COM travels in a parabolic trajectory
- Reposition segments so that the body clears the bar, whilst COM may pass under the bar.
COM applied to long jump
- better athletes lower their COM in the penultimate/last strides before take-off.
- allows for longer time to generate take off velocity during final ground contact
Balance method (finding COM)
- because COM is the point about which mass is equally distributed, it is the point around which the body is balanced.
- determine the balance point in all planes and locate the intersection.
- fine for regular shaped, single segment objects, but for humans, multiple segments means COM is not fixed.
Reaction Board method (finding COM)
- uses the principles of resultant torques and equilibrium.
- rigid board with 2 sharp supports (one on a block and the other on a set of scales)
- because the system is in equilibrium, by taking a few measurements, we can locate the COM.
Segmentation method (finding COM)
- an indirect method
- based on inertia modelling
- COM location for different segments is obtained by using photos/videos of movement combined with average segment characteristics.
Equilibrium
- a state of balanced forces and torques
- all forces and torques in all directions must equal zero
what governs stability
- base of support
- centre of mass position
Base of Support
- not necessarily in contact with the ground
- close to the edge of the BoS is less stable
- wider base of support generally increases stability and is direction dependent
Height of COM
- lowering the COM increases stability
Unstable
if pushed, a body will move and continue to move, until it reaches a stable position.
Neutrally Stable
if pushed, a body will move into a new position where it will remain.
Stable
if pushed, a body will move then return to its original position
mass in relation to stability
- measure of resistance to linear acceleration
- mass increases = greater stability
what 3 systems combine to produce balance
vestibular, visual and somatosensory systems
