To understand what is acceleration we need to first understand what is acceleration.

In scientific terms rate of change of velocity with respect to time is known as acceleration, i know you didn’t get it. In Human terms when speed of something is increasing then we can say it is accelerating. But it’s not just about increasing speed , it’s about increasing velocity with time. Velocity is a vector because displacement is also a vector which means that it has both magnitude and direction.

Now lets talk about Positive and negative acceleration.

Positive acceleration doesn’t mean object is speeding up in the same way negative acceleration doesn’t mean object is slowing down. A object with negative acceleration could be speeding up. Suppose a car is trying to climb a hill and instead of moving up it is going down due to gravity but still car engine is on and it trying. This is the example of negative acceleration where car may speed up in opposite direction due to slope. When acceleration acts in opposite direction of velocity it is called as negative acceleration.

As i told you earlier that acceleration is a vector that points in same direction of velocity.

If you think of this from Mathematics perspective then if you add to current value of velocity then it is positive acceleration but if you subtract from current value of velocity then it is negative acceleration.

Subtracting from velocity which is already negative could increase the speed of an object.

When you car is moving in x direction with some speed and you press the accelerator then it is called positive acceleration because acceleration is in the same direction as velocity so it will add.

Now suppose car is moving in x direction with some speed and you press the break then in order to stop the car acceleration must act on it from opposite direction (Newton’s First law) , therefore acceleration is in negative x direction. It will subtract form the velocity. This is negative acceleration.

## can acceleration be zero

Yes acceleration can be zero, when all the forces acting on a object cancel out each other then the net force acting is zero.

If rate of change of velocity with time is zero **( a = dv/dt = 0 )** then acceleration is zero.

When can we achieve zero acceleration – When velocity becomes constant means when velocity is not changing with time then net acceleration is zero.

In simple terms we can say an object is moving with constant speed in a same direction as displacement with net zero acceleration.