Kinematic Concepts of Human Movement (Chapter 4) Flashcards
Kinetics
Studies motion and the forces that underlie this motion.
kinematics
is solely focused on the study of motion not taking into account forces that may be acting upon the body in motion.
General motion
Combination of linear and angular motion, nearly all human movement is an example of general motion
Linear motion
movement where all body parts move at the same speed in the same direction.
Angular motion
rotation around the central axis or a fixed point
projectile motion
an object or body being acted upon when airborne
rectilinear
movement is along a straight path
curvilinear
Movement is along a curved path
Distance vs displacement
Both measure how far a body has travelled and can be used to describe motion, depending on which will provide the most useful information
- distance: measures the path travelled from start to finish (400m=400)
- displacement: is the change in position (how far it is from initial to final position)
Speed
distance (length of path) divided by time
velocity
displacement divided by time
Acceleration
a change in velocity in a given period of time.
A= final velocity-initial velocity / time
measured in m/s2
Acceleration can be either positive or negative (speeding up or down)
positive acceleration- sprinter out of the blocks
negative acceleration - bike rider maintaining balance around a corner
if acceleration equals 0, this doesnt mean the subkect is stationary, there is just no change in velocity. cross country through middle part of race trying to maintain pace.
angular motion
involves the rotation of a body around a central axis or a fixed point.
this can be seen in humans limbs around joints.
e.g running, leg rotates around hip axis (angular motion of the limbs results in linear motion of the whole body)
the axis rotation can be real or imaginary, internal/external depending on the positioning of the body.
AN external axis could be the centre of gravity when performing a tuck roll or the bar in gymnastics
Torque (what is it and how can it be increased)
Angular motion is created by a force that does not act through an objects centre of gravity that causes rotation.
torque can be calculated by multiplying the force applied by the lever. (force x lever arm)
how can it be increased:
- size of force applied (greater = increased torque)
- length of lever arm- longer lever arm = greater torque.
Angular motion- distance and displacement
angular distance: measures the path travelled from start to finish
Angular displacement: measures change in position how far from the start position is the finish
e.g gymnast completed 1 1/2 giant on the bar, distance would be 540C and displacement would only be 180
Angular speed
angular distance covered divided by the time taken.
900/4sec= 225/sec
Angular velocity
angular displacement divided by the time taken
e.g
180/4sec= 45/sec
Angular acceleration
a change in angular velocity in a given period of time
final velocity- initial velocity/time
can either be pos/neg/0
measured in degrees
300-100/s/0.5sec= 400 per sec
Newton’s laws of Angular motion
First law: angular momentum of a body remains constant unless acted upon by an external torque
Second law: a torque applied to an object will produce a change in angular motion in the direction of the applied torque that is directly proportional to the size of the torque and inversely proportional to the moment of inertia of the object.
Third: for every torque, there is an opposite and equal torque
Newton’s laws of Angular motion
First law: angular momentum of a body remains constant unless acted upon by an external torque
Second law: a torque applied to an object will produce a change in angular motion in the direction of the applied torque that is directly proportional to the size of the torque and inversely proportional to the moment of inertia of the object.
Third: for every torque, there is an opposite and equal torque
Angular momentum
the amount of angular motion possessed by an object is known as its angular momentum
Angular momentum is the product of the moment of inertia and the angular velocity (moi x av)
it is dependent on both:
- the mass of the rotating object or body (increased mass=increased moi)
- the distance the weight is distributed from the axis of rotation (mass further away from axis= increased moi)
moi
is a measure of an object’s resistance to change in its rate of rotation.
how to increase angular velocity
reduce moment of inertia (diver tucking in)
layout of pike (increasing moi) to slow down
Conservation of angular momentum
Conserved when body is in flight and can be best observed through diving, gym and trampolining
when angular momentum is being conserved there is a trade off between angular velocity and moi.
-decreased moment of inertia results in reater angular velocity
-an increased moi results in a decreased angular velocity
