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

Linear Speed and Velocity

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

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 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

Newton's Laws of Angular Motion

#2 - Law of

#3 - Law of action and reaction

#1 - Law of inertia

A rotating body wil continue to turn on its axis of rotation unless torque is applied

The angular accleration of a body is determined by the torque and takes place in the direction that the force acts on it

For every torque there is an equal and opposite torque

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

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

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

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