Defining Acceleration

Rate of change of velocity

Suppose you are travelling in a bus. The bus is driven by two kind of drivers. One driver slowly picks up the speed, and applies brakes gently whereas the other bus driver quickly picks up the speed and applies brakes very abruptly.

Which bus driver would you prefer to travel with and why?

When you are riding in a bus and there is a sudden change in velocity, you can feel this because you will fall forwards or backwards. Do you agree?
 

Do you feel the same while riding a bicycle? Can you recall at which moments do you feel such changes?

You have defined speed and velocity in previous lessons. Now let us explore acceleration.
 

Given below is the Velocity versus Time graph of a bus travelling in straight line in the same direction. Look at it carefully and try to answer the following questions:
 

     


                           

1. Is this a uniform motion or non-uniform?

2. Is the velocity of the bus changing every second?

3. What is the velocity at 1st second and at 4th second?

4. How many times has the bus changed its velocity from 0-15 meter/second?

Do not forget to fill in your reflections in the assessment box given below;

Motion is accelerated if the velocity changes.

In an accelerated motion, if the object gains speed we call it positive acceleration or simply acceleration. If the object loses speed, we say that the object has negative acceleration or retardation or deceleration. 

In the graph, there are two instances when the bus has positive acceleration. Can you identify them?