  Common Misconceptions

## Motion In A Straight Line

- What you are getting from a statement might not be necessarily true. Let's burst some of the common misconceptions
1
The acceleration of a body travelling at constant velocity.
MYTH: For a body travelling at constant velocity, the acceleration is also constant.
FACT: The acceleration is zero for a body moving with constant velocity.
The velocity of a body is defined as the rate of change of displacement whereas the acceleration is the rate of change of velocity. If the body is moving with a constant velocity, then there will be no rate of change of velocity. Therefore the acceleration of the body remains zero.  2
The sign of acceleration can predict about speeding up or slowing down.
MYTH: Positive acceleration means speeding up and negative acceleration means slowing down.
FACT: The speeding or slowing of a body is decided by the sign of acceleration along with the velocity.
The direction of acceleration cannot alone decide whether a body is speeding or slowing. There is a possibility that a body having positive acceleration but velocity is negative. In that case, the body is slowing down. Also a body can have negative acceleration and negative velocity and in this case, the body will be speeding up. Thus, velocity also plays an important role in deciding the type of motion.  3
The magnitude of acceleration of a body depends on its velocity.
MYTH: Higher velocity means higher acceleration whereas lower velocity means lower acceleration.
FACT: The acceleration is not simply the velocity. It is the rate of change of velocity.
The acceleration of a body is given as the rate of change of velocity. It means how fast the velocity of a body changes. If a body A moving at 5 m/s goes to 15m/s in time span of 2 sec and the body B moving at 20 m/s goes to 25 m/s in same time, then the body A is considered to have higher acceleration. It is because the rate of change is higher for the body A.
4
The acceleration and velocity both can determine the direction of motion.
MYTH: The acceleration and velocity both being the vector quantities involve direction. Thus, the direction of motion is predicted using any of them.
FACT: Only the direction of velocity can predict the direction of motion. The acceleration has no role in deciding the direction of motion.
The acceleration of a body is only the measure of rate of change of velocity. A body having a positive speed is supposed to move in forward direction only even if it has negative acceleration. The body would move in backward direction only once the velocity changes to negative.