# B Can any physical quantity be vectorless?

1. Jul 20, 2017

Go easy on me please as I am just delving into the world of physics and the likes :D

I may have this completely misunderstood, so bear with me and correct me where I'm wrong please.

There are 2 types of currents, DC and AC. Correct?

AC stands for Alternating Current and DC stands for Direct Current.

In a Direct Current (DC) battery for instance, the electricity flows from a + (positive) to a - (negative) source, or in other words it flows in one direction from one place to another. With an Alternating Current (AC), the electricity flows back and forth reversing its direction periodically.

A vector is something that has magnitude and direction. Magnitude is another word for 'size' and direction is the motion of an object in relation to where it is traveling. So a DC current has a vector from + to -, but what about an AC current, if it is alternating back and forth? Does it have a vector? Not only that, but in relation to the Heisenberg Uncertainty Principle, it is impossible to know the exact location of anything at any given point in time, so does anything physical in the universe have a vector?

Basically what I'm trying to say is if something is alternating back and forth, does it have a vector or magnitude of direction? If so, is it only temporary until it reverses its course and changes direction? Say for example my vector (or direction of travel) is south at 2 MPH - then I travel north at 2 MPH, and repeat this infinitesimally, does my 'Alternating Current' (or better put Alternating Direction) have a vector? If so, does it only occur temporarily? If not, than I am vectorless, or I possess no magnitude of direction in spacetime permanently, right? How can this be possible? Seems rather self-contradictory to me.

In order for something to exist, it has to have a location in space as-well as time. Right? Otherwise it has no vector or location and magnitude of direction. Hope what I'm saying makes sense and I spark some interesting conversations! :)

Last edited by a moderator: Jul 20, 2017
2. Jul 20, 2017

### Staff: Mentor

That's not such a bad question.

We usually depict AC as a rotating vector, like the hand of a clock.

Some things, like fields are spread out over lots of space and time. Yet they exist.

3. Jul 20, 2017

So was my conclusion or idea completely wrong since an AC current is a rotating vector? >.<

If so, would a non-rotating alternating current or direction be vectorless? Is it even possible for something to be vectorless?

4. Jul 20, 2017

### Khashishi

Not all physical quantities are vectors. For example, the rest mass of an object is just a value with no direction. It's a scalar.

5. Jul 20, 2017

### phinds

What direction is green? OK, maybe that's not fair since green is a characteristic, not an object. How about the charge on an electron, or better still, the charge on a sphere?

Last edited: Jul 20, 2017
6. Jul 20, 2017

### Staff: Mentor

Temperature is a common example of a field with no direction.

7. Jul 21, 2017

### HelioGeo

Is a sphere directionless? Anyway most of, if not all of the physical constants, dimensional or dimensionless, seems are presented vectorless.

8. Jul 21, 2017

### HelioGeo

Are you sure? What happens when you put a piece of ice on a hot pan?

9. Jul 21, 2017

### HelioGeo

To arrange this "rest" frame of reference, don't you refer to a direction?

10. Jul 21, 2017

### Staff: Mentor

Nice try. Heat flows from hot to cold, but that does not make a vector.

Consider the temperature of where you are right now. Does it have an up, down, north, south. East, west direction? The temperature is not the same every place but it has no direction.

Compare that with the wind field. Like temperature, wind has magnitude that varies from place to place. But wind also has direction.

11. Jul 21, 2017

### phinds

No.

12. Jul 21, 2017

### HelioGeo

Great, you are nearly saying flow doesn't make a vector? I'm in 39 C tropical area, I 'm cooling the airs around me, am I not making cold wind?

13. Jul 21, 2017

### HelioGeo

How?

14. Jul 21, 2017

### phinds

What does that have to do with vectors ?

15. Jul 21, 2017

### phinds

You misunderstand how PF works. If you make an unsubstantiable claim, it is not up to me to refute it, it is up to you to support it.

16. Jul 21, 2017

### HelioGeo

Temperatures are measures of energy state, energy flow has directions but not the state of the energy, if I interpreted correctly.

17. Jul 21, 2017

### HelioGeo

To confess, I have difficulties in understanding mass, especially rest mass and mass in general. Why should mass, an energy equivalent, has no direction?

18. Jul 21, 2017

### phinds

HUH ? You are conflating two different posts that have nothing to do with each other. Look back. My "no" was in answer to your question about frames of reference, nothing to do with mass even though you mentioned mass in your earlier post. Mass ALSO has no vector but that's a separate issue.

Look, a frame of reference is just a set of arbitrarily defined coordinates. You may choose, for example to assign your chair as a frame of reference. If you wanted to fully explicate it, you would say perhaps that your personal forward direction was the X axis and your up direction was the Z axis and off to your left was the Y axis. Now, in the rest frame of the chair, which is also your rest frame, assuming that you are not fidgeting too much, you are at rest and your mass in that frame of reference is your rest mass. What does that have to do with vectors?

If you think that the XYZ coordinate system is a set of vectors as regards the point of this thread then you are completely missing the point of the thread. Your rest mass has no vector.

19. Jul 21, 2017

### phinds

You are getting too far afield. Think simply of a sold body with a steady temperature, the same as that of its surroundings. Where's the vector? There IS a value for the temperature but there is no vector associated with it.

20. Jul 21, 2017

### phinds

@HelioGeo you may think we are being rough on you, but this is a serious science forum and poor arguments are jumped on. It's nothing personal. Attacks are only against statements/arguments, not people.

21. Jul 21, 2017

### HelioGeo

I would not associate physics to personal. Personal opinion does not change Physics!

22. Jul 21, 2017

### Khashishi

You are thinking about the gradient of the temperature. The gradient of the temperature is a vector field. The temperature itself is not.

23. Jul 21, 2017

### Staff: Mentor

You are confusing the temperature with the gradient of the temperature. The first is a scalar, the second is a vector.

One way of telling the scalars and the vectors apart is to ask yourself "How many numbers does it take to specify the value at a single given point?"; the answer will be "one" for a scalar and "three" for a vector. For example: The temperature at a single point is given by a single number, whatever a thermometer placed at that point reads; this is a scalar. The velocity of an airplane requires three numbers: rate at which the latitude is changing, rate at which the longitude is changing, rate at which the altitude is changing; this is a vector.

Last edited: Jul 21, 2017
24. Jul 26, 2017

### FrankL

Kinetic energy is an example of a physical quantity with no direction. A 1kg ball travelling right at 10 metres per second will have the same KE if it was travelling left at 10 metres per second (or any other direction for that matter). As others have said, charge is not a vector; the same can be applied to other fundamental properties, like mass, quark colour, and perhaps strangeness.

Angular displacement is not a vector because it does not obey the commutative law of vector addition. That is, you cannot add angular displacements the same way you add vectors (or natural numbers for that matter); the order makes all the difference!

25. Jul 27, 2017