a classmate in physics states that a negative acceleration always means that a moving object is decelerating?

Question

is this true?
please explain..

Answer 1

Yes!(most of the time so its partially true) But it depends upon the frame of reference and what you treat as positive or negative!

Acceleration is defined as the rate of change (or derivative with respect to time) of velocity. It is thus a vector quantity with dimension length/time². In SI units, acceleration is measured in meters/second² using an accelerometer.

Consider an object(lets say yourself) with velocity 'v' m/s
Since velocity is a vector , assume its direction along X-axis of the coordinate system(which is suppose a conveyor belt!).

If the frame of reference is fixed ( the conveyor belt in this case), then when your speed decreases due to some reason.........your acceleration is negative and your are decelerating.

Now to prove the counter point :
Let the conveyor belt be very smooth and your are holding on to some solid support which is fixed. When someone starts the belt yu remain at that spot with reference to the ground but the conveyor belt is moving ahead! In short you are decelerating with reference to the belt( - ve acceleration) but 0 acceleration with respect to the ground!!

Answer 2

It is not true. It means that the object MIGHT be decelerating but not "always" (as your friend says). Instead, think of it this way...

We start by clarifying that there is no such thing as "negative acceleration" per se. That is, that acceleration is a vector composed of an absolute value scalar and a direction. So "negative acceleration" actually refers to an acceleration which just happens to be in the negative direction of whatever coordinate system you've chosen to define for the particular problem.

We define a coordinate system (for a two dimensional universe to keep things simple) with positve/negative x and y. If the object starts out already moving in the positive X direction, then to apply an acceleration in the negative direction would mean there is deceleration. If the object is stationary or moving in the negative X direction, then applying an acceleration in the negative X direction would actually be accelerating the object. In other words, the reference from has to stay constant for there to be meaningful discourse on the subject. By the same note, even moving in the positive X direction, if the object is acclerated in the negative Y direction then the object is actually accelerating.

Answer 3

It depends on how you interpret the phrase "negative acceleration". When dealing with vectors, don't forget that direction is important!

If we look at the behaviour of an object moving in one dimension, for instance along the x-axis of a coordinate system, it can move in one of two directions: in the positive x direction, or in the negative x direction. In this system, negative acceleration would accelerate the object in the negative x direction. So, if the object was initially moving in the positive x direction, its speed would be decreasing, i.e. the object would be decelerating. However, if the object was initially moving in the negative x direction, then the negative acceleration would cause its speed to increase, and the object would not be decelerating.

OTOH, if by "negative acceleration" you mean that the acceleration is in the opposite direction to the direction of motion of the object then, at least initially, the object will always decelerate.

Answer 4

An object starts from rest and attains a speed of 10m/s in 5 second.

The acceleration is (10 -0) / 5 = 2m/s^2.

In another 5 second the car comes to rest.

The acceleration is (0-10) / 5 = MINUS 2m/s^2.

In the FIRST case, the car moves with an acceleration of 2m/s^2.

It can as well be said that the car moves with
A DECELERATION OF MINUS 2m/s^2.

In the SECOND case, the car moves with an acceleration of MINUS 2m/s^2.

It can as well be said that the car moves with A DECELERATION OF Plus 2m/s^2.

Answer 5

not true..

depends on what do you mean by "negative" acceleration and "decelerating"

an object moving at constant speed of v along a circle with centripetal force F= m * v^2/R....where R is the radius..

Answer 6

That depends on what "you" think as deceleration.
Negative acceleration would imply that the direction of acceleration is opposite to the direction of motion.
Let us assume that the object is moving east at 5 meters per second has an acceleration of 2 meters per second per second to the west. With this acceleration to the west the "speed' of the object moving east will go on decreasing until it stops. Then it will start moving west starting at zero meters per second and accelerating at 2 meters per second per second and the "speed" will go on increasing.

Answer 7

gained't get you the total mark.a extra useful thanks to placed it truly is,acceleration is in the different route(if and presented that the article is slowing down or in physics words,decelerating). for instance,your initial heading might want to properly be in the unfavourable route besides the undeniable fact that the prompt you start up decelerate,you deceleration vector factors to the effective route.this can properly be opposite direction.