# Motion

### Body In Motion - Critical Enquiry Question 3

## What does the syllabus say?

Students learn about:

· 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

- 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

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