Measuring Motion

Chapter 1 Section 1

Observing motion by using a reference point

• Reference point – an object that appears to be stationary or mobile. An object used to compare another object in motion.

• Reference direction – Used to describe the direction of an object’s motion.– Up, down, north, south, east and west

• Motion – an object’s change in position relative to a reference point.

Speed Depends on Distance and Time

• Speed – is the distance traveled by an object divided by time taken to travel that distance

• The SI unit for measuring speed is meters per second (m/s), or kilometers per hour km/h.

Determining Average Speed

• Most of the time objects do not travel at a constant speed. It is useful to calculate average speed.

Average speed = total distance

total time

Let’s Graph IT!

A Graph Showing Speed

0

100

200

300

400

1 2 3 4

Time (h)

Dis

tan

ce (

km)

Velocity – Direction matters

• Velocity – the speed of an object in a particular direction.

• Velocity must include a reference direction.

Velocity Changes

• Velocity changes only if one of the following two factors that make up velocity changes– Speed– Direction

• Constant velocity is motion in a straight line.