Re: How to calculate Angle of a rotating Vector?.


bm183 wrote:
If you use the standard orientation of the x axis and y axis so that x is positive to the right and y is positive upward, then a vector [a,b] is pointed downward if b < 0. For example the vector [ 1, -2] is pointed downward. The angle which it is pointed downward is arctan(-2/1) = -63.4 degrees.

--Lynn

lynn and randy This is the true result from my calculations and the error
occurred via my fault because I did not specify the y pointing downwards
nor calculate the angle properly

OK. These numbers now match up a *little* closer to your
verbal description, but still not completely.

... and now you can say the vectors are rotating clockwise
because the angles are getting smaller and larger

That would not be my description of something rotating
clockwise. Something rotating clockwise would be steadily
progressing in the same direction. There is no steady
progression here. Instead, there is an alternation in sign.

The hour hand on a clock moves clockwise. Does it
every once in a while start moving from 3 to 2 to 1
instead of from 1 to 2 to 3?

as the rotation progresses so there is a pattern of some type taking place.

Other than alternating in sign, I see no pattern here.

And I will pose my question in case you don't want to go through all
the posts again, given AB what is the angle of BC given BC
what is the angle of CD and so forth.

Unless you have left something out, there is no way to
predict what the angle of BC is given the angle of AB.

VECTOR X Y VECTOR TAN-ANGLE
AB 112.50 201.3 230.60 60.80
BC 131.00 -195.9 235.66 -56.23

Let's just start here. Is there any particular reason this
endpoint is where it is? Could it have equally likely been
at -70 or -40 or -32.7 or -65? I don't see any reason
why not, unless there's something special about the
point C you aren't telling us.

There is no apparent rule here. Your question has
no answer. Based on what you've told us, each
direction is (within some limits perhaps) random.
Perhaps it is randomly chosen between 45 and 75
degrees, for instance.

Also, I'll ask this question a third time since you've
chosen not to answer it the first two times: You say
these vectors are fixed in length, yet the table clearly
shows the length between points is not fixed in
length. Why do you describe them as "fixed in
length"?

I suspect there's a lot you aren't telling us about what
this process represents.

- Randy

.

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