Question

Can an object have zero velocity but nonzero acceleration? can it have zero acceleration and nonzero velocity? WHY?

Answer 1

Think about gravity acting on a ball going up. There is a negative acceleration slowing the ball down. Does the ball reach zero velocity at some time?

Answer 2

The ball will keep slowing down until it has zero velocity and then after that it will start speeding up again but in a downward direction. All the time the acceleration is a non-zero constant.

Answer 3

So for instance, when the ball goes up it reaches a point where its initial velocity reaches 0. So it's acceleration and velocity are zero? Im a bit confused with that. Im guessing that the ball does reach zero velocity at some point when it comes down and stops...

Answer 4

The acceleration never goes to zero.

If I throw a ball that goes 10 m/s and it decelerates at 2 m/s^2 in 1 second the new velocity will be 10-2=8 m/s
In 2 seconds it will be 10-2(2)= 6 m/s
at 5 seconds it will be 10-2(5)= 0 m/s
at 6 seconds it will be 10-2(6) = -2 m/s, the negative sign means it is going in the opposite direction.
At 5 seconds the speed was zero, but the acceleration was stil 2 m/s^2

Answer 5

speed or velocity is the rate something changes distance per unit of time
acceleration is the rate that speed or velocity changes per unit of time
If something is decelerating or slowing down, eventually it will stop and if the acceleration continues it will speed up in the opposite direction.

Answer 6

The second part can be explained with Newtons first law of motion which says that an object will stay still or move a constant speed unless a force makes it accelerate. That means if an object is going 5 m/s and the acceleration is zero, it will always go 5 m/s a non-zero velocity with zero acceleration

Answer 7

Oh okay. Thank you so much! I understand it more clear now.

Answer 8

Not quite agreeing with @plainntall
acceleration never goes to zero?!?!?!
you have to consider some cases
let's say net external force go to zero. F=ma so a=0
imagine a person jumping off the sky from a jet. He will reach terminal verlocity, which means after some time the velocity would reach a constant value. this is zero acceleration, I believe

in order to understand the relationship between accecleration, I think getting through the definition is quite a nice way. In this sense I appreciate your comment on the definition ;)

Answer 9

to be in short I give 2 cases where the mentioned can be fulffilled.
case A is when you drop a ball down (free fall). Initially the velocity is zero because it was at rest. But by gravity the acceleration will be non-zero and downwards.
case B is newton's first law. If there is no net external force on the body, it will either stay at rest for ever or go at constant velocity.
Well, I think seeing the physics in every case and understanding the forces will do much good.

Answer 10

And duh.... From definition, zero acceleration means constant velocity, where v=c and c may not nessacerily be identical to zero at all case. (see v1 and v2)
And zero velocity is only a point on a v-t graph. the instantaneous acceleration cannot be determined to be identical to zero as well. (see v2 and v3)

Answer 11

I am not sure what you mean. The question asked if the acceleration can be non-zero and have a velocity of zero. I gave an example for such a case much like you did where the acceleration is constant such as the acceleration due to gravity and just for an instant the velocity is zero at the maximum height of freefall motion with an initial upward velocity.

Usually people try to understand kinematics, the mathematical description of motion, before they delve into Force and Newton's laws of motion. I tried to stick to as qualitative a description as I could so as not to exacerbate the confusion.