Question

Is acceleration upward has positive or negative acceleration?

Answer 1

Using up and down is many times not that useful: Consider the gravitational attraction between two planets, each with an inhabitant asking your question....and say one throws a ball up in the air.....he sees it deccelerating away from him while she sees it decelerating towards her on the distant planet.

Another way to get a perspective on "positive" and "negative" is to realize that gravitational potential is taken to be zero at infinite separation and negative when objects are closer...in other words, positive work must be done to separate the objects. You have to do positive work to move a balls upwards. This is in fact the convention used in physics and is why it is said that the total energy in the universe is zero...gravity offsets everything else.

Answer 2

whether you call something positive or negative depends entirely on what direction you've assigned as "positive".

a FRAME OF REFERENCE is imperative in physics so that you can keep track of directions more easily

Answer 3

Just to add to @JFraser

You can choose any direction as positive - the key thing is that you remain consistent.

If you measure distance as positive in a given direction , then velocity and acceleration must also be positive in that same direction.

Answer 4

The acceleration of a body moving in the upward direction from the earth, only under the influence of force of gravity, is taken as negative since the velocity decreases with respect to time

Answer 5

The velocity decreases in the direction that YOU have chosen to define as positive.

Any consistent frame of reference will be OK.

Answer 6

Is the acceleration increasing or decreasing ie is the velocity increasing or decreasing in the upward direction?