Theory Flashcards
Scalar
Has magnitude only
Mass, energy, power, work.
Vector
Has magnitude and direction.
Force, moment, velocity, acceleration.
What are the characteristics of a cross product of two vectors?
- Magnitude equal to the product of magnitudes of the two vectors multiplied by sine of the smaller angle between the two.
- Direction perpendicular to the plane defined by the two vectors.
- Sense: Right hand rule
Kinesiological Analysis
Data integration and correlation. Anthropometry Kinematics Kinetics/Dynamometry Electromyography
Anthropometry
- Body
Bone and segments (structure, proportions)
Kinematics
- Movements
Distance
Angle
Velocity and acceleration
Kinetics/Dynamometry
- Forces
Linear forces
Moment/torque
Pressure distribution
Electromyography
- Muscle activation
Muscle action
Potentials
Function
In mathematics, it is a relation from a set of inputs to a set of possible outputs, where each input is related to exactly one output.
CoP - Center of foot pressure
The neuromuscular response to the imbalance of the body’s center of mass CoM. CoP controls the position of CoM.
EMG
Electro myography
EMG signal
Based upon action potentials at the muscle fiber membrane resulting from depolarization and repolarization process.
Motor unit
Functional unit of a motor system.
- Motoneuron actin on a skeletal muscle fiber.
Motor unit action potential
sum of action potential which differs in form and size depending on geometrical fiber orientation in ratio to the electrode site.
Raw EMG signal
Unfiltered and unprocessed signal detecting the superposed MUAP.
Recording EMG (Exam)
- Locate
- Clean
- Place
- Connect
- Visualize
Raw EMG range
Can between +/- 5000 microvolts (athletes).
EMG frequency contests ranges between 6-500 Hz, showing most frequency power between 20 and 150 Hz.
Nyquist-Shannon sampling theorem
Establishes a sufficient condition for a sample rate that permits a discrete sequence of samples to capture all the info from a continuous time signal.
F sampling ≥ F max
Frequency of a measuring device needs to be twice as much as the frequency being measured.
Frequency
Number of occurrences of a repeating event per unit of time. Nr. of actions in a second.
Derivative of functions
Used to determine slopes, maximums, minimums etc.
Represents the slope of the graph of a function.
Represents the instantaneous rate of chance.
Integration of functions
Opposite of differentiation.
Used to calculate areas, volume, amount of work or energy etc.
Represents the area under a curve.
Can be definite or indefinite.
Force
A vector
A push or a pull exerted by objects on other objects.
Come in pairs.
Accelerates or deforms an object.
Torque
Related to rotational and twisting action of applied force. Newton’s 3rd law, action / reaction.
Moment
Related to the bending effect.
Moment of force.
Forces producing rotation/bending.
Newtons 1st law of motion (Exam)
Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
Expresses the concept of inertia of a body: it’s reluctancy to start moving, or stop moving once it has started.
Newtons 2nd law of motion (Exam)
The relationship between an object’s mass (m), it’s acceleration (a) and the applied force is F=m*a. The direction of the force vector is the same as the direction of the acceleration vector.
Forces are unbalanced ∑𝐹≠0 𝑁
There is an acceleration
-> The acceleration depends directly upon the “net force”
-> The acceleration depends inversely upon the object’s mass
Newtons 3rd law of motion (Exam)
For every action there is an equal and opposite reaction.
Uniform motion
Constant speed, constant direction
Centripetal motion
Constant speed, changing direction.
When turning.
Internal forces
Forces that are generated by muscle contractions.
Normal force
Perpendicular to the surface.
Tangential force
Parallel to the surface (friction force).
Compressive force
Shrink the body.
Together with tensile force result in bending.
Tensile force
Stretch or elongate the body (muscle force).
Together with compressive force result in bending.
Colinear force
All the forces have a common line of action.
Coplanar force
All forces are on the same plane (2D).
Concurrent force
Lines of action have a common point of intersection.
Parallel force
The line of action of the forces are parallel to each other.
Gravitational force
Force exerted by earth on an object.
Weight is the force of gravity acting on the mass of the body.
Pressure
The larger the surface the smaller the pressure.
How much load in percentage is on the L3 while laying, standing, sitting, leaning forward and sitting and leaning forward?
Laying: approx. 25% Standing: 100% Sitting: approx. 140% Leaning forward: approx. 150% Sitting and leaning forward: approx. 190%
Mechanical stress
Distribution of force within a body, quantified as force divided by the area over which the force acts.
Amount of mechanical stress is inversely related to the size of the area on which the force is spread.
How much force is sustained every time a foot hits the pavement while running? (Exam?)
Two to three times the body weight.
Frictional forces
Two surfaces in contact when one slides over the other. Depends on the nature of the sliding surfaces and material.
Does not depend on surface area.
Static force
Proportional to the normal force (N) and always act in a direction tangent to the contact surface.
Equilibrium.
The force applied before the object starts moving.
Tops at Fmax.
Linear.
Kinetic force
Proportional to the normal force (N) and always act in a direction tangent to the contact surface.
Motion.
From when the object starts moving.
Constant.
Moment
Measure of the ability of a force to produce a turning effect around an axis.
The axis is perpendicular to the line of action of the force.
The bigger the d the greater the moment.
If the line of action of a force passes through the axis of rotation (O), that force generates no moment (d=0).
Net movement - Mnet
Sum of the vectors of moment of force around the same axis.
Clockwise moment +
Counter-clockwise moment -
Magnitude of vector always positive, just when we calculate Mnet we put +/-.
First class lever
Fulcrum(center of rotation) located between the effort (muscle pull) and the load (weight).
Advantageous and disadvantageous.
Second class lever
Load (weight) is between the fulcrum (center of rotation) and effort (muscle pull).
Advantageous.
Third class lever
The effort (muscle pull) is between fulcrum (center of rotation) and load (weight). Disadvantageous.
Rule of levers
If the effort is closer to the fulcrum than the load, it is disadvantageous and vice versa.
Systems in equilibrium
When the acceleration of a body is 0, the body is in equilibrium.
When the velocity of a body is 0, the body is in static equilibrium or rest.
Free body diagram
- Constructed to help identify the forces and moments acting on individual parts of a system.
- The parts constituting a system are isolated from their surroundings.
- The effects of the surroundings are replaced by proper forces and moments.
Active Forces
Externally applied loads and gravitational forces.
Reactive forces
Constraining forces and moments acting on a body (usually unknown). Exerted by the ground supporting elements.
Pulley
Perfectly transfer forces in any direction around it (frictionless system).
Same force magnitude but changes direction.
Statics in equilibrium
Area of applied mechanics, which is concerned with the analysis of rigid bodies in equilibrium.
You have moment always when there is a rotating movement.
Static and kinetic friction forces
If object is: Resting at equilibrium -> Fs = F applied About to move -> Fs = μs * N = Fmax Moving at a constant velocity -> Fk = μk * N = F applied
