i have seen the acceleration due to gravity expressed using a negative sign. -9.8m/s/s

can someone explain if this could be a correct way to express g...

thank you

It's all about defining your directions. Once you pick one as positive, the opposite direction must be negative.

Up is usually defined as positive. In this set of coordinates, since gravity is a downwards force, g is -9.8 m/s

There's nothing to stop you from defining down as the positive direction. In this case, since gravity now acts in the same direction as you have defined as positive, it would have to be +9.8 m/s²

so expressing g as a negative integer isn't necessarily wrong, depending on how the directions are defined.

for example a rocket (or anything else for that matter that is traveling in a positive direction relative to the ground) would have a -9.8m/s/s acceleration due to g.

where as a sky diver (or anything traveling in a negative direction relative to the ground) would have a +9.8m/s/s acceleration due to g.

therefore, g can be expressed both as a negative and positive rate of acceleration, correct?

quote:

Originally posted by ChrisWaTm:
so expressing g as a negative integer isn't necessarily wrong, depending on how the directions are defined.

Correct. As for your examples, however, it is not the direction of travel that is important. It is just how you define your directions.

A skydiver would experience a 9.8 m/s² acceleration downward. It's up to you whether you define up as positive (in which case both the skydiver's acceleration and his velocity are negative) or down as positive (in which case both the skydiver's acceleration and his velocity are negative).

Likewise for the upwards moving rocket, except that now (assuming something hasn't gone wrong) the velocity and acceleration have opposite directions. If you define up as positive, the rocket will have a positive velocity but a negative acceleration. If you define up as negative the rocket will have a negative velocity but a positive acceleration.

It is more typical to define up as positive and down as negative, but there is nothing fundamental about that. Either way of looking at the problem gives you the same final result.

quote:

Originally posted by ChrisWaTm:
for example a rocket ... would have a -9.8m/s/s acceleration due to g.

A rocket, that is, with its engine off, and not far enough from the earth's surface to feel a pull of gravity less than g.

God, Devil and physicists.
=================
In 1906, Rutherford studied internal structure of atoms,
bombarding them with high energy a- particles.
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But the clever Devil interfered and gave advice to physicists to enlarge the target.
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But this, he has withheld from man.
He has not explained that the Vacuum is infinite and inexhaustible.
And in infinity there is contained an infinite variety of particles.
And by bombing the vacuum, one can find centaurs and sphinxes.
But my God, save us from their presence on Earth.
=================.
Rutherford was right.
His followers are mistaken.
Why?
Imagine, that I want to plant a small apple- tree.
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It is normal.
But if to plant a small apple- tree, I shall begin to dig
a base for a huge building (skyscraper),
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will you call me a normal man?
=========================.
Imagine a man who breaks watches on the wall.
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As many as the scientists have who aspire to understand
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If not take into account the initial conditions of Genesis,
the fantasies of the scientists may be unlimited.
================== .
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The science can not eternally develop to “mad infinity.”
==========================.

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