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“Acceleration is defined as the rate of change of velocity of a body.”In many cases the velocity of a body changes due to a change either in its magnitude or direction or both.The change in the velocity of a body causes acceleration in it.If an object is moving at a constant speed but changes its direction as it moves (such as whirling a stone attached to a string or if an object is moving in a straight line but changes its speed as its moves (such as in a 100 m sprint),both objects are accelerating.

### Acceleration formula

Taking **a **as a acceleration ,initial velocity as Vi ,final velocity as Vf and t is time interval ,SI unit of acceleration is meter per second per second ms^{-2 }

## What is average acceleration in physics?

The average acceleration of a body given in the above equation is a during time t.Let the time t is divided into many smaller intervals of time.If the rate of change of velocity during all these intervals remains constant then the acceleration a also remains constant.Such a body is said to possess uniform acceleration.

## average acceleration formula

**Uniform acceleration in physics**

“A body has uniform acceleration if it has equal changes in velocity in equal intervals of time however short the interval may be.”

## Difference between positive and negative acceleration

**What is positive acceleration?**

Acceleration of a body is positive if its velocity increases with time.The direction of this acceleration is the same in which the body is moving without change in its direction.

## Examples of positive acceleration

- When the train leave the station its velocity increases with increasing of time,this is the example of positive acceleration.
- When we start a vehicle its velocity increases with time,this is positive acceleration.

**What is negative acceleration?**

Acceleration of a body is negative if velocity of the body decreases.The direction of negative acceleration is opposite to the direction in which the body is moving. Negative acceleration is also called deceleration or retardation.

## Examples of negative acceleration

- When a train reaches at station its velocity decreases with time,this type of acceleration is called negative acceleration.

similarly:

In example,an elevator moving upward (which we take to be the direction of positive velocity ) cane accelerate upward with positive acceleration and move faster or accelerate downward with negative acceleration and move slower.When it is moving downward with negative velocity ,it can accelerate downward with negative acceleration and move slower.When the acceleration and velocity have positive signs ,so that the speed (the magnitude of the velocity) is decreasing,we refer to a deceleration.

**How do you calculate the Acceleration due to gravity?**

“The acceleration of freely falling bodies is called gravitational acceleration.”Drop an object from some height and observe its motion.Does its velocity increase,decrease or remain constant as it approaches the ground?Galileo was the first scientist to notice that all the freely falling objects have the same acceleration independent of their masses.

External sources

- http://formulas.tutorvista.com/physics/acceleration-formula
- http://www.physicsclassroom.com/class/1DKin/Lesson-1/Acceleration

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