Chapter 7 Motion & Forces 7.1 Describing Motion 7.2 Forces

7.1 Describing Motion

Motion Motion is the process of changing position in relation to a reference point. Reference point Motion

Reference Point and Position Reference Point and Position A reference point is the starting point we use to describe the location or position of an object. Position describes an object’s distance and direction from a reference point.

Example: Sports fields use markings to show the reference point of a player or object

Direction Direction is which way you should travel to arrive at the new position. examples: Left, right, over, under, north, south, east, west

Distance And Displacement

Distance Distance is the entire path from start to finish. Example: red path point A to B (4m) point B to C (3m) = 7m

Displacement Displacement is the difference from the starting point to the final position. It is the most direct route between two points. Example: black path point A directly to point C is 5m

Speed and Velocity

Speed & Velocity Speed & Velocity Speed is the distance an object travels in a unit of time

Example A cyclist travels 50m in 25 seconds. What is his speed? Speed = distance/time 50m / 25s = 2m/s

Types of speed Constant speed An object moves the same distance over a given unit of time Changing speed T he distance an object covers increases or decreases over a given time

The stick figure represents a person’s movement over time Which shows a constant speed ? Answer : b Which shows a changing speed ? Answer : c and d

Average Speed Most things in motion do not travel at exactly the same speed during the entire trip Example : cars stop and go regularly runners go slower uphill than downhill It is more accurate to use average speed.

Velocity Velocity describes the speed and direction of an object

Types of Velocity Constant velocity An object moves with a constant speed and it’s direction does not change. Changing velocity Velocity changes when either the speed or direction of motion changes

Showing Velocity The length of the arrow = speed The head of the arrow = direction

A. C. B. D. Which arrow shows the slowest speed? D Which arrow indicates an object moving quickly to the west? A Which arrow represents an object moving slowly south? B

Acceleration Acceleration is a change in speed or direction Positive acceleration speeding up or changing direction Negative acceleration or deceleration slowing down or changing direction

Rollercoaster Physics A rollercoaster is speeding up, slowing down, and changing direction. It has a changing velocity. Since the velocity is changing, so is the acceleration