Need a better definition of anticlockwise

  • #1
198
4

Main Question or Discussion Point

Dictionary says it is the opposite of clockwise. But if a clock is transparent and you look at it from behind, the same direction that was anticlockwise before is now clockwise. So it seems to depend on the point of view. But there are some electromagnetic equations that depend on clockwise versus anticlockwise. So it is not just a mathematical concept that depends where you're looking at it from, but the universe has it hard-wired in its laws. What would be a more profound definition of anticlockwise?
 
Last edited:

Answers and Replies

  • #2
13,252
10,211
You are asking about an orientation in a rotation motion. Hence you will need a coordinate system, especially an angle ##\varphi##. Then ##\varphi \longmapsto e^{i\varphi}## is anticlockwise and ##\varphi \longmapsto e^{-i\varphi}## clockwise.
 
  • #3
198
4
The coordinate system too is drawn in a certain... wiseness which is by convention. Or is it not by convention but there is a fundamental reason to put the x axis to the right, the y to the top and the z towards the viewer?
 
  • #5
13,252
10,211
These things are conventions. You cannot distinguish between left and right if you have no orientation. And an orientation is by definition related to something given, the coordinate system.

The cross product orientation is defined by left and right hand. So the coordinate system is given by the person's position to the experiment.

In any case you need a gauge.
 
  • #6
828
293
Stepping back from clever math, you have 'Faraday's Thumb'. If electrons travel 'thus', the magnetic field wraps 'so'...

Still gotta choose a sign convention, though, which is why us kids were bemused by 'Conventional Current'. Which, in turn, had its little joke of showing up as 'holes' in eg NPN silicon devices...
 
  • #7
Klystron
Gold Member
691
944
Stepping back even further, an anthropology professor referred to clockwise as "sunwise" (North America). Old lore defines counter-clockwise as "widdershins" (Northern Europe).
 
  • #8
13,252
10,211
Stepping back even further, an anthropology professor referred to clockwise as "sunwise" (North America). Old lore defines counter-clockwise as "widdershins" (Northern Europe).
IIRC the maps the ancient Greek and Romans used had Africa in the north and the Alps in the south. So from an anthropological point of view ...
 
  • Like
Likes Klystron
  • #9
Klystron
Gold Member
691
944
With the advent of digital clocks I visualize the rotation of the Earth as viewed from the north for counter-clockwise. So, earthwise?
 
  • #10
198
4
You cannot distinguish between left and right if you have no orientation. And an orientation is by definition related to something given, the coordinate system.
You cannot but nature can apparently. It has laws such that the one that generates the Lorentz force on a particle. This force distinguishes clockwise and counter-clockwise, see #5.

EDIT: or maybe B's direction (towards the north pole) is purely a convention. Introduced by people on the hemisphere where Europe lies. But I'm sure there are other laws that have the cross product in them and they do not apply to arbitrary directions like that of B.
 
  • #11
13,252
10,211
Whether you all a certain orientation clockwise or counter-clockwise, left handed or right handed, left or right, up or down, positive or negative has not the least to do with nature.
 
  • #12
198
4
Look, there is a law of nature that includes a cross product. Don't you think you should account for it too.
 
  • #13
13,252
10,211
Your thread title has asked for a definition of clockwise. This is a deliberate human name for a certain rotation. A rotation which depends from which side you look at it. There have been several helpful comments given to you.

Nature might have processes which are oriented, but how you call this orientation, and a definition is nothing else, has nothing to do with nature.

I have the impression what you really want to know is, why certain physical quantities behave according to the left hand rule and not the other way around. But this cannot be answered. Have a look at:
 
  • Like
Likes Klystron
  • #14
198
4
So if there is a separate civilization on Australia that has not had any contact with us up until the middle ages, and develops its own science where they draw maps upside down (and their campuses point to their version of north, the Antarctic), and they make their clocks run like their version of sunwise, then when this civilization discovers the motion of charged particles in a magnetic field, would they make different predictions for their motion or would they derive the same law but with a negative sign in front of their cross product and that's ok, different cultures different laws of nature?
 
  • #15
13,252
10,211
... would they make different predictions for their motion ...
No.
... or would they derive the same law but with a negative sign in front of their cross product and that's ok, ...
Yes.
... different cultures different laws of nature?
No.

The same laws, different names, different conventions.
 
  • #16
1,599
960
No discussion of "clockwise" is complete without a discussion of nonconservation of parity. I will simply recommend the master Richard Phillips Feynman:

 
  • Like
Likes pinball1970
  • #18
198
4
Alright try this. We stick a negative sign in some laws NOT by convention but to say that an opposition takes place, here's one such law:

https://en.wikipedia.org/wiki/Lenz's_law
We don't stick a negative sign wherever convention requires it. Name a law of physics where a negative sign is the result of convention!
 
  • #19
13,252
10,211
Of course this is a convention. Physics won't change if we substituted ##\Phi_B## by ##-\Phi_B##. You simply moved the point of convention to another place.
 
  • #20
198
4
Lenz law's negative sign is a result of convention? It relates to RATE of change, it would be the same for the hypothetical Australian civilization.
 
  • #21
13,252
10,211
Why is one rate called negative and the other one positive? What's a negative rate for ##\Phi_B## is a positive rate for ##-\Phi_B##.
 
  • #23
13,252
10,211
This thread is running in circles.

Thread closed.
 
  • Like
Likes YoungPhysicist and weirdoguy

Related Threads on Need a better definition of anticlockwise

  • Last Post
2
Replies
41
Views
3K
Replies
5
Views
13K
Replies
4
Views
2K
Replies
4
Views
615
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
2
Views
963
  • Last Post
Replies
7
Views
713
  • Last Post
Replies
2
Views
2K
Top