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Biomechanical Kinematic Concepts (Newton's Laws of Angular Motion (#2 …
Biomechanical Kinematic Concepts
Motion
Linear motion
occurs when the body moves in a straight or curved path where all body parts move in the same direction at the same speed. If the line is straight, it's called
retilinear motion
. If the line is curved, it's called
curvilinear motion
.
Angular motion
occurs when there is no movement around a central axis.
General motion
is the combination of linear and angular motion.
Angular Distance and Displacement
Angular distance
is the sum of all angular changes the body undergoes while rotating.
Angular displacement
is the difference between the initial and final angular position
Linear Speed and Velocity
Speed = distance/time
and
Velocity = displacement/time
. Speed and velocity are measured in metres per second (m/s) but can also be measured in km/hr or mile/hr
Linear Distance and Displacement
Distance
measures how far the body has travelled from start to finish.
Displacement
measures the change of position from the starting position
Linear Acceleration
Acceleration = change in velocity/change in time
. Can be +ve or -ve. An acceleration of 0 means that they are not increasing or decreasing speed but are still moving
Angular Motion
Involves
rotation
around an axis. The axis can be imaginary, internal or external
Torque
Any action that causes an object to change its rotary motion. Angular motion occurs because an unbalanced force is applied outside the body's axis of rotation which causes a change (
TORQUE
). Angular motion responds to torque in the same way linear motion responds to force
Angular Momentum
The amount of angular motion possessed by a rotating body. The smaller the MOI and greater the velocity, the harder it is to stop an object's angular motion
Conservation of Angular Momentum
The total momentum of a body stays constant until an unbalanced torque acts on the object. Divers are able to move from an open position into a tuck position which decreases MOI and increases velocity which conserves angular momentum
Newton's Laws of Angular Motion
#2 - Law of
The angular accleration of a body is determined by the torque and takes place in the direction that the force acts on it
#3 - Law of action and reaction
For every torque there is an equal and opposite torque
#1 - Law of inertia
A rotating body wil continue to turn on its axis of rotation unless torque is applied
Moment of Inertia
The greater the amount of inertia, the more difficult to change the rotation. (
e.g. in surfing, short and light boards are easier to change rotation than long and heavy boards
)
Short application of moment in inertia:
Equipment is modified for kids to reduce the MOI (smaller and lighter tennis racquets); equipment is modified to distribute weight; human body can alter its position and distribution of mass
Angular Speed and Velocity
Speed = angular distance/time
and
Velocity = angular displacement/time
. Angular speed and velocity are measured in degrees per second
Angular Acceleration
The rate of change of angular velocity. Can be +ve, -ve and zero