How can: an accelerating object with a negative velocity have a positive acceleration?

explain to me how you define an accelerationg object as having a positive vs. negative acceleration, not direction.


how can


an accelerating object with a positive velocity have a positive acceleration...


BUT ALSO


an accelerating object with a negative velocity have a positive acceleration?


the tutorial im reading says:


The general RULE OF THUMB is:


If an object is slowing down, then its acceleration is in the opposite direction of its motion.


this RULE OF THUMB can be applied to determine whether the sign of the acceleration of an object is positive or negative, right or left, up or down, etc. Consider the two data tables below.


in Example A, the object is moving in the positive direction (i.e., has a positive velocity) and is speeding up. When an object is speeding up, the acceleration is in the same direction as the velocity. Thus, this object has a positive acceleration.


In Example B, the object is moving in the negative direction (i.e., has a negative velocity) and is slowing down. When an object is slowing down, the acceleration is in the opposite direction as the velocity. Thus, this object also has a positive acceleration.How can: an accelerating object with a negative velocity have a positive acceleration?
acceleration is changing the direction of motionHow can: an accelerating object with a negative velocity have a positive acceleration?
It's slowing down. A negative velocity can be interpreted as a motion from right to left, and a positive acceleration will bring it to a stop. A continuation of the positive acceleration will cause it to start moving to the right. Both the velocity and acceleration are positive to the right.
Acceleration is the rate of change of velocity over time.





Imagine yourself in a car traveling in reverse, lets say at 20 mph. Now imagine the car still going backwards, but going slower, now at 15 mph 5 seconds later. Your velocity is still negative at -15 mph but your acceleration is toward the front at 5 mph/ 1 seconds or one mph per second. This might seem counter-intuitive because of the signs. (It is easier to think of it as deceleration in a negative direction, but two negatives make a positive, right)


But think of it like this, if your acceleration remains constant then in another 5 seconds you will be going backwards at only 10 mph. 5 seconds more and you are only going 5 mph backward. Another 5 seconds later and you are at a dead stop for a second and now starting to travel forward instead of backward. Another 5 seconds and you are traveling forward at 5 mph and accelerating forward even faster. Our acceleration has not changed but now that the car has changed direction and is traveling forward, it might be easier to see that the acceleration is positive.


The object with negative velocity will probably not keep its negative velocity long with a positive acceleration. It will eventually slow to a stop and then develop positive velocity.





I hope this helps a little
Traditionally, an object moving along a graph from left to right is said to be moving in the positive direction, while an object moving from right to left is said to be moving in the negative direction.


This is merely a convenience - after all, an object can't really have a negative speed.


The sign merely indicates the direction of the motion.


The same convention applies to the object's acceleration.





Remember that the velocity and the acceleration of an object are two separate things.


The velocity is the rate of change of position, while acceleration is the rate of change of velocity.
Acceleration is the measure of the force applied - so an object slows down as a result of an accelerating force applied against the direction of motion.





Another way to say it is that the object in motion is not accelerating (either positively or negatively), it is being acted on by an outside agent (force) which has positive acceleration.