CBSE Class 11-science Answered

It is very important to notice that acceleration is defined in terms of a change in velocity - not speed. This may seem like a minor point, but it isn't. Since acceleration is the rate velocity changes,

You are accelerating whenever you:

• speed up - This is not difficult to grasp, since it is the common conception of acceleration.
  
  
• slow down - People commonly call this deceleration, as if it were physically different from the "speeding up" case - but to a physicist, it's all the same - if your velocity is changing, you are accelerating.
  
  
• change direction - This one can be tough to grasp. Since velocity is your speed and direction, your velocity changes if your direction changes (even if your speed stays the same). Since you are accelerating if your velocity is changing, you are accelerating when you are changing direction - even if your speed stays the same

Since acceleration is linked to changes in velocity - when your velocity is changing, you are accelerating, students often get the misconception that "acceleration is a change in velocity". NO!! Acceleration is the rate at which the velocity changes - there's an important difference!

To say that "acceleration is a change in velocity" is like saying "velocity is a change in position" (This does sound silly, doesn't it?). Velocity tells you how fast position is changing. Acceleration tells you how fast velocity is changing.

Acceleration is not a change in velocity!