# Motion

## What does the syllabus say?

· motion

- the application of linear motion, velocity, speed, acceleration, momentum in movement and performance contexts

Students learn to:

· apply principles of motion to enhance performance through participation in practical workshops

Basic biomechanics part 1

## Video

This video talks about motion. in the video you learn about linear motion, angular motion, and general motion until around the 3 minute mark of the video

## Study/Summary Notes

Acceleration

Acceleration is defined as the rate at which velocity changes with respect to time.
• average acceleration = (final velocity - initial velocity) ÷ elapsed time
From Newton's 2nd law:
• Force = Mass x Acceleration
• Acceleration = Force ÷ Mass

Speed and velocity

Speed and velocity describe the rate at which a body moves from one location to another. Average speed of a body is obtained by dividing the distance by the time taken and average velocity is obtained by dividing the displacement by the time taken e.g. a swimmer in a 50m race in a 25m length pool who completes the race in 71 seconds - distance is 50m and displacement is 0m (swimmer is back where they started) so speed is 50/71= 0.70m/s and velocity is 0/71=0 m/s
• Speed and Velocity = distance travelled ÷ time taken

Momentum

Momentum is a vector describing a "quantity of motion" or in mathematical terms p (momentum) = mass (m) times velocity (v).
p=mv

Conservation of Momentum

In a closed system, such as when two objects collide, the total momentum remains the same, though some may transfer from one object to the other. Momentum is always conserved in a closed system, but most sporting situations in the real world are not a closed system. For example, when a baseball bat hits the ball, the ball will be squished to a certain degree. After few milliseconds, it rebounds back. This contraction and rebound action is causes the release of heat energy, and some momentum is lost, or transferred elsewhere.

Maximising Momentum

As momentum is the product of mass and the velocity, you can increase momentum by increase either of these elements. In sport, examples include using a heavier bat or racquet and increasing running speed or hand speed.

Angular Momentum

Angular momentum is the product of Moment of Inertia and Angular Velocity. Moment of Inertia is the angular counterpart to mass - it is the measure of the resistance of an object to changing its angular speed.
A good example of angular momentum in action is with figure skaters. A figure skater starts a spin by pulling in his arms to lessen his Moment of Inertia. By the Conservation of Momentum Principles, the angular speed must then increase. To come out of the spin, a skater simply extends her arms to increase angular momentum and decrease angular velocity.

## Practise Questions

1. Outline the key points associated with the biomechanical principles influencing movement

2.Describe the difference between speed and velocity

3. Explain the application of acceleration and momentum in relation to swinging a basketball