negative acceleration?

Question

i know what it is but how do i explain it?

ok i said this negative acceleration is when the final speed is less than the initial speed.
does that sound understandable?

ok wow i am soooooooo confused! i like to put very general answers that are not so detailed that way i would have a less likey chance to get them wrong but thanks to all of you that were corect even thought i dont know who is because im still soooo confused by this....

Answer 1

In terms of vectors, it's acceleration in the opposite direction
OR
In terms of how you and I normally think, it's just deceleration.

Slowing down = negative acceleration.

Answer 2

To a point, yes. But what if you accelerated for 10 minutes and then decelerated for 1 minute? Your final speed is still higher than your initial speed, in this sense you accelerated in the larger sense, but in terms of derivatives, acceleration and deceleration are instantaneous. It would be more correct to say that negative acceleration is when you velocity is decreasing (a=dv/dt => a is negative if your velocity is decreasing) and positive acceleration is when your velocity is increasing. This is completely separate from talking about intial or final speed. Also note that even if your speed is increasing your velocity might not be in the mathematical sense. If you have a negative velocity and apply a negative acceleration, then your velocity will decrease (i.e. get more negative) but this could be perceived as an increase since the magntitude (not sign) of the velocity is increasing. You have to ignore this, because the sign on everything matters.

Answer 3

It is an increase in velocity in the negative direction.

If velocity is in the positive direction, you are slowing down. If velocity is zero or in the negative direction, you are speeding up.

EDIT

Your explanation is partially correct. Generally, I would state that negative acceleration is when final velocity is less than initial velocity. This would take into account the fact that velocity is a vector (depends on direction) where speed is only a scalar. Your explanation only holds true if and only if your velocity is positive, which is not always the case.

Answer 4

WHOA WHOA WHOA!!!

Slow down. Negative acceleration is NOT decceleration (aka acceleration in the opposite from the "direction of motion") and if you use that as your basis you're going to have some pretty serious sign errors in any calculations youd.

When you diagram a problem you begin by choosing reference frames INCLUDING which directions are positive or negative. therefore ANY velocity in the positive direction is positive and in the negative direction is negative. ANY acceleration in the positive direction is ALWAYS positive whether you are speeding up or slowing down. (for example, an object moves in the negative direction... it's velocity is - 5 m/s, a force is applied to in the positive direction. It LOSES velocity, but you MUST calculate with a POSITIVE acceleration or the problem doesn't work)

People tend to think of negative acceleration being simply DECELERATION because they fail to remember that in physics you don't change your frame of reference halfway through a problem.

Summary: negative acceleration is any acceleration that is in the opposite direction (NOT of motion but rather) from what you have chosen to consider the positive direction of travel.

Answer 5

There is no such thing as deceleration.

Negative acceleration is acceleration opposite to the direction of motion.

Answer 6

Deceleration

Answer 7

Explain it in terms of what?
It's deceleration.
It's the opposite of acceleration.
It's a change in velocity where the velocity is decreasing.

You should ask your teacher what exactly he's looking for in this explanation.