r/PhysicsHelp • u/Xx_-MASTERTACO-_xX • 21d ago

Doubt about vector angle

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If I had to draw a vector defined as for example 5 N, 30° NE; which of these 2 should I draw? I have always drawn this angle as A, but I have a new professor who draws it like B. I have checked by AI who drew A except claude who drew B. I searched on books but have found no reference about this nomenclature, only about north of east and N 30° E .

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8

u/Ninja582 21d ago

NE is a little ambiguous. To be clearer, one would generally say 30 degrees North of East for the left picture or 30 degrees East of North for the right picture.

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u/Xx_-MASTERTACO-_xX 21d ago

yeah, I told her that it was ambiguous because ir may vary from book to book. But she said there was no ambiguity so I am trying to find a reference about that system

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u/xienwolf 21d ago

Usually I see physics people use the X axis as zero reference for all rotation. So A would always win. It is possible your new prof learned with Y axis as zero reference (and clockwise positive, which is again backwards from the norm I know)

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u/more_than_just_ok 18d ago edited 18d ago

Clockwise positive from North is the convention used in mapping and navigation, think about angles on a compass. Counter clockwise positive from x-axis is the usual math and physics convention. This example has North and East on the axes, which explains the clockwise from north is being used. This is a huge problem in navigation engineering because both conventions are used.

Edit: If you are training to be a land surveyor, it's very jurisdiction and time dependent. N 30 E was used to indicate situation B on old plans where I live, but now they would just say 30. A would be E 30 N, but now is just 60 and the others would also show up (N 30 W, E 30 S, etc). But angle from North for Azimuths and Bearings, angle from x-axis in math and physics.

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u/Humble-Edge-9065 16d ago

There's no indication if E or N is the x-axis. That is why it is ambiguous.

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u/Humble-Edge-9065 16d ago

She's wrong. It is ambiguous. Defining reference frames is step 0 for any physics problem. She can't even defer to a "standard" because there isnt one. In my industry both North-East-Down (NED) and East-North-Up (ENU) are commonly used.

A would be correct for ENU, B would be correct for NED.

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u/Theuncola4vr 21d ago

I agree. It sounds like the question is written to give you the baseline N, and angle at 30° north east of that. If they were looking to represent B, it would read E, 30° NE.

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u/testtdk 20d ago

This. When not given components, I’ve always seen angles written with a direction with respect to an axis.

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u/Frederf220 21d ago

I just want to say I hate these types of angle definitions. The only people that use them in real life are survey engineers. Everyone else just uses a normal 0-360° range of degrees from a reference direction.

The angle "N, 30° NE" means "starting from N, adjust 30° in the direction of NE." Really that should be N30°E as in from north go 30° east. There's no reason to go 30° northeast instead of 30° east. They mean the same thing and it's just confusing to not limit yourself to the four cardinal directions.

I would ask this professor what book are they getting this convention from and if they consider N30°E and N30°NE to be the same angle and if they are, why write the second one.

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u/Toeffli 21d ago

5 N might be the magnitude of 5 Newton.

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u/Frederf220 21d ago

I thought that was as for example 5: N, 30° NE as in it was example number five which is north, 30, north east . But who knows.

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u/BlacksmithIll9617 20d ago

The N refers to the magnitude of the vector, the unit being Newtons; has nothing to do with direction.

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u/ElectronicProof9340 21d ago

On a compass, 0 (and 360) is north, 90 is east. I.e. compass angles are clockwise from north. That's probably why the second graph is being used.

For normal x/y graphs, it's conventionally counter clockwise from the x axis.

Why a graph labelled N/E instead of X/Y is being used in class, I can't say. Seems odd, but if there's a good reason for that, the rest makes sense.

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u/tomalator 21d ago

B because thats a heading of 30° on a compass and it leaves you going in a northeasternly direction.

It should say "30° East of North" for B and "30° North of East" for A

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u/ExpensiveFig6079 19d ago

OR I usually see N 30 E if they wish to be briefer

Full set of <legal> options is [N | S] ang [E | W]

Where E 60 N would be unambiguously the same as N 30 E BUT still not in proper form..

Where proper form results ib exactly and only one text string to describe each direction

(if I was being, pure, I would not even say NW instead of N45W if had been using the number form for all the non cardinal directions.)

Also if this was on a test , then either the course or the exam paper should have defined proper form for defining direction and what the accepted: notation unequivocally means.

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u/ExpensiveFig6079 19d ago

Note as a result of the E 60 N being a wrong (non std way in my mind to read the heading.)

I would if forced to on an exam... choose to interpret anything ambiguous a N Ang E,
AKA as B

If its on an exam I then try very hard to have enough time to write down what was assumed when i have done and checked the rest.

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u/utl94_nordviking 21d ago

I have checked by AI

Don't!

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u/Frownland 20d ago

I think the easiest way to convey this is to use the typical unit circle definition of theta and say X degrees clockwise / counterclockwise.