What does having negative of any of these mean? Thanks!
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The sign of the velocity tells you which direction the object is moving in. So, if the velocity is positive, you know the object is traveling in the positive direction. Note that which direction is positive is completely arbitrary. The physical reality is that the object is moving in some direction. Whether we call that direction positive or negative is completely up to us. So when I say the object is moving in the positive direction, I mean it is traveling in the direction I chose to be positive.
A negative velocity just means the object is traveling in the direction I chose to be negative.
The sign of the acceleration is similar, in that it tells you the direction of the acceleration (time rate of velocity change). So, if the acceleration is positive, it means the velocity is changing in the positive direction. Here's the tricky part: there are two ways for the velocity to change in the positive direction. If the velocity is positive, a positive change makes it even more positive (i.e., the object speeds up). But if the velocity is negative, a positive change still makes it more positive, but that's less negative, so the object slows down.
If the velocity is negative, it means the velocity is changing in the negative direction, and I'm sure you're not surprised that there are two ways for this to happen. If the velocity is negative, a negative change makes it even more negative (i.e., the object speeds up). But if the velocity is positive, a negative change still makes it more negative, but that's less positive, so the object slows down.
A negative velocity just means the object is traveling in the direction I chose to be negative.
The sign of the acceleration is similar, in that it tells you the direction of the acceleration (time rate of velocity change). So, if the acceleration is positive, it means the velocity is changing in the positive direction. Here's the tricky part: there are two ways for the velocity to change in the positive direction. If the velocity is positive, a positive change makes it even more positive (i.e., the object speeds up). But if the velocity is negative, a positive change still makes it more positive, but that's less negative, so the object slows down.
If the velocity is negative, it means the velocity is changing in the negative direction, and I'm sure you're not surprised that there are two ways for this to happen. If the velocity is negative, a negative change makes it even more negative (i.e., the object speeds up). But if the velocity is positive, a negative change still makes it more negative, but that's less positive, so the object slows down.
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It means the direction relative to some reference velocity and/or acceleration...typically the initial velocity and/or acceleration. See these examples:
V = U + AT; where U is the reference initial velocity, V is the end velocity, and A is the acceleration over time T. The plus means the acceleration is in the same direction as the initial velocity, which also has a plus sign (even though it's not shown here).
V = U - AT; the minus means the acceleration is in the direction opposite to the plus U velocity. It is slowing the speed down. And of course, we call an acceleration that is decrementing the speed deceleration. Also note that the final V will turn negative; it will have reversed from its initial direction.
V = - U - AT; the - A means the acceleration is in the direction of the initial velocity, which, as you see, is also negative. As this A is adding its negative value to the negative velocity, it's increasing the velocity in the negative direction; so this is not...not...deceleration, it's acceleration.
V = - U + AT; this is in fact, deceleration. As the acceleration is in opposition to the initial velocity that velocity is being slowed down. Its value is becoming more and more positive until, given enough time T, it will actually go positive.
V = U + AT; where U is the reference initial velocity, V is the end velocity, and A is the acceleration over time T. The plus means the acceleration is in the same direction as the initial velocity, which also has a plus sign (even though it's not shown here).
V = U - AT; the minus means the acceleration is in the direction opposite to the plus U velocity. It is slowing the speed down. And of course, we call an acceleration that is decrementing the speed deceleration. Also note that the final V will turn negative; it will have reversed from its initial direction.
V = - U - AT; the - A means the acceleration is in the direction of the initial velocity, which, as you see, is also negative. As this A is adding its negative value to the negative velocity, it's increasing the velocity in the negative direction; so this is not...not...deceleration, it's acceleration.
V = - U + AT; this is in fact, deceleration. As the acceleration is in opposition to the initial velocity that velocity is being slowed down. Its value is becoming more and more positive until, given enough time T, it will actually go positive.