Kinematics & Kinetics Flashcards
What is kinetics?
The study of the action of forces
The study of the motion with respect to time and forces
What are the types of general motion?
Linear motion
Angular motion
What is linear motion?
Motion along a line that may be curved or straight with all parts of the body moving in the SAME DIRECTION at the SAME SPEED
What is angular motion?
Motion that involves rotation around a central line or point
What are the types of linear motion?
Translation
Rectilinear
Curvilinear
Define “Translation”
PURE Linear motion
When a body experiences translation, it moves as a unit and portions of the body do not move relative to each other
Define “Rectilinear” motion
Motion along a straight line
Define “Curvilinear” motion
Motion along a curved line
In angular motion, what is the axis of rotation?
The imaginary line perpendicular to the plane of rotation and passing through the centre of rotation
What is general motion?
Motion that involves both linear and angular motion simultaneously
What are movements in the sagittal plane?
Elbow flexion/extension Wrist flexion/extension Finger flexion/extension Knee flexion/extension Ankle dorsi/plantar flexion
What are coronal plane movements?
ABduction & Adduction
What are transverse plane movements?
Medial rotation
Lateral rotation
Define speed, with equation.
Speed = distance covered with respect to time
Speed = distance % time
Define velocity with equation.
Velocity = time rate change of displacement
- velocity is the change of distance in a specific direction
Average velocity = displacement (distance in a direction) % time
Define acceleration with an equation.
Acceleration = the time rate of change of velocity
- Velocity varies therefore so does acceleration
Average Acceleration = change in velocity % change in time
What is a vector?
A vector is a quantity that has both MAGNITUDE and DIRECTION
Therefore both VELOCITY and ACCELERATION are vector quantities
What is vector resolution?
Vector resolution replaces a single vector with 2 perpendicular vectors so that the vector composition of the original vector yields the original vector
Solved using tip-to-toe method (forming right angled triangle)
Therefore solved using Pythagoras theorem
- c^2 = a^2 + b^2
What are the trigonometric solutions to vectors?
Sin(angle)= opposite % hypotenuse [SOH]
Cos(angle)= adjacent % hypotenuse [CAH]
Tan(angle)= opposite % adjacent [TOA]
What is angular distance?
The angle through which an object rotates from one position to another about an axis of rotation
What is angular displacement?
The smaller of two angles (with respect to a scale of 360degrees) between initial and final positions following a period of rotation
Define angular speed with an equation
Angular speed = the rate of change in angular distance
Average angular speed = angular distance % time taken to cover
Define angular velocity with an equation
Angular velocity = the rate of change of angular displacement
Average velocity = angular displacement % time
Define angular acceleration with equation
Angular acceleration = the rate of change of angular velocity
Average angular acceleration = change in angular velocity % time
What is the unit of measurement in angles used in rotational movement?
Radians
Define radian
The length of an arc divided by its radius
1 radian = 360degrees % 2pie = 57.3 degrees
Define linear kinetics
The relationship between force and change in linear kinematics
Define angular kinetics
The relationship between force and change in angular kinematics
Define Inertia
Resistance of an object to action or to change
Inertia is the tendency of a body to maintain its current state of motion, whether it is motionless or moving with a constant velocity
It has no units of measurement
What is the mechanical definition of inertia
Resistance to acceleration
How is inertia related to mass?
The amount of inertia the body possesses is directly proportional to its mass
The more massive an object is, the more it tends to maintain its current state of motion and the more difficult it is to disrupt that state
Define mass
The quantity of matter contained in an object
Common unit kg
Dependent on density and volume
Define force
A push or pull acting of a body- the product of mass and acceleration
Each force is characterised by its magnitude, direction and point of application to a given body
Measured in Newtons
1 N is the amount of force required to accelerate 1kg at 1m/s^2
What are the two types of force?
Explain these types of force
Contact force
- result from physical contact between objects eg collision
- eg impulse - is the product of the magnitude and duration of a force
Attraction force
- forces that tend to attract objects towards each other
- eg body weight = attraction du to gravity
Define momentum
The product of a mass of an object and its linear velocity
What are Newtons 3 laws?
First law = law of inertia
Second Law = law of acceleration
Third Law = law of reaction
What is Newtons First Law of inertia?
A body remains at rest or in a state of constant motion in a straight line unless it is acted upon by an applied force
The state of motion is described by the body’s momentum (p), defined as the product of its mass and linear velocity
P=MV
If no force is applied to a body, it’s momentum will remain constant
Define Newtons Second Law of acceleration
- The time rate of change of the linear momentum of a body is equal to the force applied to it
- Force will cause the body to accelerate in direct proportion to the magnitude of the force and the same direction of the force
- Describes how a rigid body moves when external forces are applied to it
What is the equation of Newtons Second law of acceleration?
F=ma
Can also be a = f%m
(When a force acts on an object, acceleration is inversely proportional to the objects mass and directly proportional to the magnitude of the force)
Define Newtons Third Law of reaction
When one body applies a force to another, the second body responds with an equal and opposite reaction force to the first body
What is Newtons Law of gravitation states
Force is directly proportional to the product of the masses of the two objects
and
inversely proportional to the square of the distance between the two objects
Bodyweight is the product of mass and acceleration due to gravity
What is a centre of gravity?
- A body’s centre of gravity is the point around which the body’s weight is equally balanced, no matter how the body is positioned
- It is the point of which the line of action of the weight of an object acts irrespective of the position of the object
- From a kinetic perspective, the location of the centre of mass determines the way in which the body responds to external forces
What is Centric force?
When force is applied through the centre of a body and then the body will be translated in the direction of the applied force
What is eccentric force?
If a force is applied through a point other than the centre of the body, the body will undergo both translation and rotation
What is the rotary effect created by eccentric force?
Torque
What is torque?
Rotary effect created by eccentric force
It is the angular equivalent of linear force
Torque is the product of force (F) and the perpendicular distance (d)
T=Fd
The greater the amount of torque acting at the axis of rotation, the greater the tendency for rotation to occur
Define a lever
A lever is a rigid free bar which is free to rotate around a fixed pint called the FULCRUM
The position of the fulcrum is fixed so that it is not free to move with respect to the bar
Levers are used to lift loads in an advantageous way and to transfer movement from one point to another
What are the 3 classes of lever?
- The fulcrum located between the applied force and the load
- The fulcrum is at one end, the force is at the other end and the load is in between
- The fulcrum is at one end, the load is at the other end and the force is in between
What is a free body diagram?
A sketch that shows a defined system in isolation with all of the force vectors acting on the system
Means of presenting the forces, moments of force and geometry of mechanical systems
What are the steps in solving mechanics problems?
Step 1 = free body diagram
Step 2 = use the free body diagram to derive the equations of motion of the object
Step 3 = know the numerical values are submitted and equations are solved for the unknown terms
How do you construct a free body diagram?
- draw object of interest in minimalist form
- write out the coordinates of the object to specify its position
- indicate the objects centre of mass with a marker; draw accelerations from here
- draw and label all external reaction forces, basing directions on how the object experiences them
- draw all Unknown forces and moments with positive coordinate system, Unknown forces must be applied wherever the body is in contact with the environment or other bodies
- draw and label global coordinate system axes off to the side of the diagram indicating which are the positive directions
Define compression as a mechanical load on the human body
- Compressive force can be thought of as a squeezing force
- the amount a tissue can tolerate without rupture
Define tension as a mechanical load on the human body
- tension is the opposite of compressive force - tensile force
- tensile force is a pulling force that creates tension in the object to which it is applied
- ## muscles produce tensile force that pulls on the attached bones
What is Youngs Modulus?
It is the ratio of stress to strain
What is Hookes Law?
It is as stress increases, strain increases in proportion to it
Define Shear as a mechanical load on the human body
- Shear force acts parallel or tangent to a surface
- Shear force tends to cause one portion of the object to slide, displace or shear with respect to another portion of the object
Define mechanical stress as a load on the human body
Stress = the distribution of force within a body, quantified as force divided by the area over which the force acts
Pressure represents the distribution of force external to a solid body, STRESS, represents the resulting force distribution inside a solid body when an external force acts
Define bending as a mechanical load on the human body
Asymmetric loading that produces tension on one side of a body’s longitudinal axis and compression on the other side
Common in vertebral disc injury
Define torsion as a mechanical load on the human body
TORSION occurs when a structure is caused to twist about its longitudinal axis, typically when one end of the structure is fixed
TORSION is load producing twisting of a body around its longitudinal axis
Torsional fractures of the tibia are common in football and skiing
What is it called when more than one mechanical load is applied to the human body?
Combined loading
What is kinematics?
- The study of motion
- without reference to force
