why cant something have a negative velocity?

Question

PLEASE explain

im only in 8th grade

it sais that in my homework

ppl say it does, so what do i write down??!?!?

Answer 1

I'll repeat my answer below. don't be afraid to say something CAN have a negative velocity if you can argue it. As I said, it's just semantics. Don't sweat it. You have more important things to learn in physics than whether a particular convention allows velocities to be negative.
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It can. If you define positive as north, then something going south has a negative velocity.

Now when it comes to describing a vector quantity in terms of a magnitude and direction, then it is true that we don't generally use negative magnitudes. A vector with magnitude -5 and a direction of north would customarily be described as magnitude +5 and direction south.

But this is just a semantics question really. There's no physics in it to be worried about.

Answer 2

Objects CAN have a negative velocity. Velocity is by definition gives a magnitude(Speed) and direction (+/-) on a coordinate system.
Speed cannot be negative since it only gives the magnitude.
In laymans terms: the difference between speed and velocity is that you could desribe and object moving 10 ft/1sec as a speed, but if you were describing the object's velocity you would have to include a direction as well: Assuming left is negative and right is positive an object moving left 10 feet in a second would have a speed of 10ft/sec and a velocity of -10ft/sec.
Make sense? Velocity is magnitude with direction (again, the +/-) whereas speed is merely the magnitude.

Answer 3

your book says something can't have a negative velocity????? What kind of book is this?
Don't confuse yourself with speed and velocity. In Physics, speed and velocity are two different things. speed has only a magnitude and no direction, thus it can only be positive or zero. Velocity has a magnitude and a direction, thus it can have a negative value.

Answer 4

You cannot have negative speed.
It is possible to have negative velocity (speed + direction).

speed is distance over time. Time flows only one way and distance is a mathematical construct which, by definition, must always be positive (or zero). Distance cannot be negative.

However, velocity can be signed.
Radial velocity is the component of the object's velocity that is along the line joining the observer and the object. For example, a galaxy as seen from Earth (the other component, sideways, is called "proper motion").

Radial velocity is determined by observing the spectral lines of a known gas (e.g.. hydrogen) and seeing how much their frequency has been lowered by the speed at which the galaxy is moving away from us (Doppler effect). For visible light, a lower frequency means that the spectral lines are moved to the red side of the spectrum (as opposed to the blue side). The result is called: redshift.

You take the observed frequency and the standard frequency (found in labs), enter that into an equation, and out comes the radial velocity.

In some rare cases, the galaxy is actually moving towards us and its lines are blueshifted. When we enter the frequencies into the equation, we get a negative radial velocity (this tells us that the direction is the reverse of the usual recession).

However, negative velocities are only used in one dimension. For example, if you are using only the x-axis.

If you are using a two-dimension graph, the velocity is kept as its two elements: speed and direction. For example, 27 km/s towards direction angle 47 degrees. (The "velocity" is the combination of the two elements; it is not only the "27 km/s" part).

Therefore, the "speed" part of the velocity must follow the rules for speeds (never negative).

Answer 5

You say it can have a negative velocity.

Argue your position. That is the point of Science

When you are reversing a car, you are going in the negative
x-direction. You will have a negative velocity

Velocity has a direction

- 10 m/s or 10 m/s

Your speed is 10 m/s, but which way are you going?

Answer 6

You can have a negative acceleration ,if you are slowing down.
Acceleration is a change in velocity
Velocity is speed in a given direction.
You set the direction, so change in the direction is a change in the velocity, but not negative velocity.
If you set up a number scale -5,-4,-3,-2,-1,0,1,2,3,4,5
You could show velocity in an east or west direction,
E<------------- * -------------->W
But the opposite direction is not a negative velocity.

Answer 7

Since velocity is the measurement of speed over distance, an object that isn't moving can't have it.

Answer 8

This Site Might Help You.

RE:
why cant something have a negative velocity?
PLEASE explain

im only in 8th grade

it sais that in my homework

ppl say it does, so what do i write down??!?!?

Answer 9

Either you're moving at a positive speed FROM zero, or you're AT zero.