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3.1 Speeding up and slowing down:

Non-uniform motion

Imagine you are What happens when an object changes its speed?
sledging down a hill … When an object changes its speed, it can either increase it (speed up) or

and then going down decrease it (slow down). This means that the initial speed of the object is
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an escalator in the different from its final speed. The motion is no longer uniform because
underground. How are the speed is no longer constant. When we have different speeds for a
moving object, we are able to calculate the average speed.
these types of motion
different? average speed (m/s) = total distance travelled (m) / total time elapsed (s)
Also, if we know the initial speed and the final speed of the object, we
can calculate the average speed as:

v average = (v final + v initial) / 2

ACT Consider the motion of a car. It covers distance d at a speed of
1
60 km/h, distance d at 75 km/h, and distance d at 65 km/h. What is the
2 3
car’s average speed?

1 The speed camera is
mounted next to the road.

2 The infrared camera, linked to a
computer, records the vehicle’s
registration number.

3 The camera records the exact time the vehicle crosses 2 chosen
points on the road. The computer calculates the time the vehicle
takes to cover this distance, and then the vehicle’s speed.
How a speed camera works

DID YOU KNOW?

Often, to control the traffic, the police use speed cameras to check
if drivers are speeding. The camera takes two photographs of the
vehicle at two different time intervals. The road markings allow the
camera to calculate the distance travelled and thus calculate the
average speed.

REMEMBER! When an object covers non-equal distances per equal
time intervals, this is called non-uniform motion.
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