# Can't we say vector or scalar quantity is relative thing

1. May 27, 2010

### samieee

Can't we say vector or scalar quantity is relative thing!!

We all know that physical quantities are expressed as vector or scalar quantities.Now let consider 'area',if I say my house is 2000 sq.feet in that sense area may be called scalar but area of a surface is a vector quantity[either upward or downward direction].Now another example is pressure.It is much debatable whether pressure is scalar or vector.So we can solve the dilemma by saying that the whole thing is relative,don't we?

2. May 27, 2010

### JDługosz

Re: Can't we say vector or scalar quantity is relative thing!!

The 'area' is a scalar. The specific shape of some square is a vector. Saying "2000 square feet" loses information as to whether it is long or skinny, or golden ratio, or square; as well as which direction is normal to that floor plan.

3. May 27, 2010

### samieee

Re: Can't we say vector or scalar quantity is relative thing!!

yes area is scalar but some specific cases it is vector[area of surface or plane] so can't we call it relative thing?

4. May 27, 2010

### Nabeshin

Re: Can't we say vector or scalar quantity is relative thing!!

Ever heard of tensors? The world is not completely described by scalars and vectors alone.

Your point is somewhat moot, because the same applies with speed and velocity. When we don't care about direction, it suffices to simply use speed, as in 1/2 m v^2. Similarly, when we don't care about the orientation of a given surface, we can simply use its area, without a specified normal vector. The exact same thing applies for pressure. It's not relative, and in a sense you could argue that these quantities are fully described by a vector and we merely chop off the unnecessary information (make them scalars) when it is convenient for us. But it's certainly not relative. What it is is arbitrary, since for a given surface the choice of normals is completely by convention. It's really not a dilemma at all.

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