In this topic we are learning to: z Consider what it means for an object to accelerate. z Measure and calculate accelerations. z Predict the motion of objects experiencing accelerations.
Acceleration
Objects do not always move at a constant speed. They speed up and slow down.
When speed changes over time, it is called acceleration. The formula for acceleration is:
Acceleration = Change in speed (m/s) Time taken (s)
Unit of acceleration = m/s/s, or m/s2
Speeding up or slowing down
An acceleration that causes the speed of an object to increase is simply known as acceleration. An acceleration that causes the speed of an object to decrease is known as a deceleration.
Using this knowledge, what do you think the function of an accelerator in a car is?
For example, if the speed of a car changes from 15 m/s to 25 m/s in four seconds, then the acceleration of the car can be calculated as:
Acceleration = Change in speed Time
= (25 – 15) 4
= 10 4 = 2.5 m/s2
This means that every second, the speed of the car is increasing by 2.5 m/s: Four seconds later ...
15 m/s 25 m/s
Initial speed = 15 m/s Fig. 17.2.1
Acceleration = 2.5 m/s2 Final speed = 25 m/s
Acceleration is a vector quantity, so it takes place in certain directions. This means that acceleration can also be described as how quickly velocity changes.
