# Quick Simple Physics Question

godkills
When a car starts up from rest and then 4 seconds later it comes to a rest again; is there motion after the 4 seconds? Is there Distance if so can it be calculated and how graphically?

Well my common sense is telling me no because when a car starts up there is motion and while there is motion it is making a distance because it is traveling.

So when a car stops it is not making any distance at all and it has no motion.

Homework Helper
That sounds perfectly correct. Do you have any reason to think that is incorrect?

That is the meaning of "motion" in English, changing position.

godkills
No, I am just starting to learn physics in school also one more question, Is velocity speed?

I am getting some conflicts when I am doing problems in the textbook where some times you use the speed as velocity in some equations. Where you use the term v as speed? And I may know that sometimes using x can sometimes define velocity. Or all the letters are just representing something more specific meaning that sometimes it can be defined as (y) and then sometimes it can be defined as (z)

My instructor explained on the first day saying that speed is a scalar and velocity is a vector.

And when I Google by definition it defines velocity as speed?

also just to ensure my understanding v subscript 0 and v itself defines as velocity always?

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koyalsiteribo
vectors have magnitude and direction, whereas scalars only have direction, so velocity is speed with direction

v0 is initial velocity

godkills
So speed is a vector and it is velocity correct?

koyalsiteribo
no -- speed is a scalar and velocity is a vector

speed does not equal velocity though

examples of speed could be: 1 m/s, 8 m/s
examples of velocity could be: +1 m/s, -8 m/s

in terms of physics, it's incorrect to say that speed is velocity, just as it is incorrect to say that 8 m/s = -8 m/s

the magnitude of velocity, however, is speed
ie, the magnitude of -8 m/s is its absolute value, which is just 8 m/s

godkills
Ahh you have caught me, So magnitude is speed and magnitude belongs to the scalar category.

Magnitude in measurements is always positive because speed is never negative.

That sound correct?

godkills
bump?

gamma5772
As stated, velocity is a vector quantity -- it has magnitude and direction. Speed is the magnitude of velocity, and is therefore a non-negative scalar.