Question

If a ball is thrown straight up and at its highest point what would the balls acceleration be

Answer 1

-9.8m/s^2 downward if the positive y-axis is set to be upward..

Answer 2

In simple words the acceleration downward is 9.8m/s...

As @k142 the acceleration can also be described by -9.8 m/s but what does it imply?

This implies that acceleration is in opposite direction or against something

This can also be called retardation or deceleration

Ball is accelerating downward by 9.8 m/s due to the gravity or in other words ball is accelerating upwards negatively by -9.8 m/s second until the acceleration of the ball is 0 and ball comes at rest and then falls down on the EArth(It's acceleration is decreasing by 9.8 ms/(or -9.8)

Answer 3

@adjax your statements seem completely incorrect. I strongly recommend looking at an elementary physics book before coming here to give help.

First, you said "Ball is accelerating downward by 9.8 m/s due to the gravity or in other words ball is accelerating upwards negatively by -9.8 m/s "

It is not true because the ball is always accelerating by the same acceleration 9.8m/s^2 either downward or upward depending on the direction of the the positive y axis: it never changes, irrespective of whether the ball is moving upward or downward.

Second, you said "... until the acceleration of the ball is 0 and ..."

When it comes to a rest it doesn't mean it has a 0 acceleration. The acceleration is still -9.8m/s^2 but what happens is just the change in the direction but not decreasing the acceleration down to zero. It is a false statement made too often by every, sometimes advanced, student.

Third, the figure you sketched is utterly false.

Answer 4

I haven't gave my answer according to graph-based perspective of yours but more of a layman way..the rigors behind a concept can be told later.

1.) "Ball is accelerating downward by 9.8 m/s due to the gravity or in other words ball is accelerating upwards negatively by -9.8 m/s "

By This I meant (again in layman terms)..that ball do is going upwards and it do posseses all the properties of motion such as acceleration,velocity(all interlinked with each other)...

But due to the gravitational attraction it's acceleration is decreasing by 9.8 m/s^2(due to the to-the-rigor perspective all terms are properly aligned[until there's a spell mistake] in this answer)

or it's slowing down in simple words.....

And by the way by -9.8m/s^2 I referred to your graph-based perspective

And yes as you said acceleration is still -9.8 m/s or can we say it as gravitational
constant of the earth g

\[g = 9.8m/s^2\]

I

And by decrease in acceleration I mean the acceleration of the rigid body which is constantly getting decreased due to the attraction of the gravity...Otherwise the ball should always go up(why should it fall down then?..remember:the mass has a tendency to remain in its stat either moving or at rest[According to the newtonian mechanics])

"When it comes to a rest it doesn't mean it has a 0 acceleration"

I also doesn't mean that it come to 0 acceleration literally .SInce anybody/anything can't have 0 acceleration on the earth(or any thing which have suffiecient gravity in layman terms but (rigors-now) everything accelerates bodies towards itslef but that's neglible for very small bodies[bodies which have low mass..clarified otherwise you'll put up an arguement of the blackhole]) all of us are being accelerated towards the earth by the rate of 9.8 m/s^2 all times(even when we are on the land)..


IN CONCLUSION:

I just only tried to explain why there's a minus(or '-') sign there [-9.8m/s^2]....which is the same thing you told from the graph-based perspective(the direction)...

I only tried to explain it more easily in a layman view...I think all of your rigors are satisfied now...

My diagram only tried to convey that while body is accelerating upwards it at the same time is also getting decelerating or slowing down due to the gravity of the earth

AT LAST:

I know what you meant and you are right but:

"...ball is always accelerating by the same acceleration 9.8m/s^2 either downward or upward depending on the direction of the the positive y axis: it never changes, irrespective of whether the ball is moving upward or downward..."

Can I also put up a to-the-rigor question here?

:HAPPY JUG-FILLING CURIOSITY: :)
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Answer 5

@k142: Thank you for pointing out some irregularities in my analogies :)

Answer 6

I think that there are still things you should explain since I can't seem to get them all as why everything on the Earth can't have a zero acceleration. Whether any object can have a zero acceleration or not would definitely depend on which reference frame you are referring to @adjax.. you should explain this.