Linear Kinetics & Angular Kinetics Flashcards
What are the two branches of kinetics?
Static - a condition in which a body/object is at rest.
Dynamic - a condition in which a body/ object is in motion.
Define force.
The pushing or pulling action this body has (Newtons).
Define net force
The resultant of all forces affecting an object.
When does equilibrium exist?
- the net force on a body is zero.
- the resultant of all forces acting upon the object is zero.
Define an internal force.
Force acting within the system under investigation.
Define external force.
Force acting on a system due to the interaction with its environment.
What 5 things is force characterised by?
- magnitude
- rate of development
- contact time
- frequency of application
- location of application
Define mass.
Amount of matter in a body (constant value).
Measure of the inertia of a body (measured in kg).
Define inertia.
The resistance of a body to change motion.
Define weight.
- the gravitational force attracting a body towards the earth.
- measured in Newtons.
- different to mass (varies).
- weight is a force and is directly related to mass.
- weight (W) = mass (m) x gravity (g)
What is the force exerted by gravity?
9.81 m/s2
Define momentum.
The quantity of motion (linear or angular)
Give the equation of linear momentum.
Linear momentum = Mass (m) x Linear Velocity (v)
What is force application affected by?
Mass and weight of a performer.
Define impulse.
The product of force and the time over which force is applied.
Give the equation for impulse.
Impulse = Force (F) x time (t)
Define kinetics.
- The branch of mechanics that deals with the causes of motion.
- Concerned with the forces that act on a system.
- Basis for understanding kinetics is the concept of force.
Why investigate kinetics?
- explains underlying cause of the movement pattern of technique.
- provides an explanation of the musculoskeletal demand of movement
Application of kinetics.
Informs the coach in terms of overload AND specificity.
- key for effective skill development.
- key for effective strength and conditioning.
What does net magnitude depend on?
Horizontal and vertical force
Name and explain Newton’s 1st law.
Law of inertia.
Every body continues in its state of rest or motion in a straight line unless compelled to change that by forces exerted upon it.
Name and explain Newton’s 2nd Law.
Law of acceleration.
The rate of change of momentum of a body is directly proportional to the force causing it and the change takes place in the direction in which the force acts.
Name and explain Newton’s 3rd law.
Law of action-reaction.
To every action there is an equal and opposite reaction.
Define work.
- Product of a force applied on a body and the distance the body moves in that direction in that time.
- Work = force x distance
- measured in Joules (J)
Define power.
- The rate at which a force does work.
- power = work/time
- power = force x velocity
- measured in Watts (W)
Define energy.
The capacity to do work.
Measured in Joules (J).
What is used to measure external forces?
Dynamometers e.g load cells, force plates, instrumented equipment.
Define load cell.
A transducer that is used to create an electrical signal whose magnitude is directly proportional to the force being measured.
What are the 3 phases of the counter-movement jump?
- Preparation for take off
- Flight
- Impact/landing
When does max GRF occur?
Early in the push off phase
What is the formula for the rate of force development (RFD)?
RFD = Fp/t Fp = peak force
What is the formula for jump height (m)?
h=1/2gt2
During a penalty kick, a footballer applies an average force of 102N to a 0.4kg ball for a duration of 0.12s. What is the impulse applied to a ball and the velocity of the ball?
Impulse = 12.24 N/s Velocity = 30.6 N/kg/s
Define angular kinetics.
Branch of mechanics that deals with the causes of angular motion
Define torque.
A tendency of a force to cause a rotation about an axis.
Define eccentric force.
A force that does not act through the pivot point.
Define moment (torque) arm.
The perpendicular distance between the force and pivot.
What is the formula for torque?
T=F•d
Give examples of moments of force in sport.
Muscle force.
GRF.
Gravitational force.
What is a force couple?
- a pair of forces
- equal in magnitude
- opposite in direction
- cause rotation but not translation
Define equilibrium.
Sum of the clockwise moments = sum of the anti-clockwise moments
Define Moment of inertia.
The resistance of a body to change in angular motion.
Dependant on mass distribution about an axis of rotation.
What is the formula for moment of inertia?
I=m•r2
What is angular impulse?
Angular Impulse = rate of change in angular momentum
