Angle of rotation versus radius of rotation

trigo

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Mar 21, 2020
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I am working on a problem and I need to convert radius of rotation to angles of rotation. So there is a point moving on a line in R^2. The point will change trajectory by turning. There is a constraint to the turning. The point has a minimal radius of rotation to respect (let's call it r). I would like to obtain the maximum angle between the original trajectory and the new path. Of course I could choose a arbitrary close point on the circle and compute a slope and then the angle.

So for example. let the point be at P(-1,0) for t=0. It will start turning from that point (r=1). It was moving on the line x=-1 to the positives. It will "turn right" bounded by the circle (x-1)^2+y^2=^2. I don't see how calculus may help. The point was already running on the tangent line of the circle. So my idea was to choose a point on the circle and compute a slope. But later I will need to compare different angles with different speed. So the choosing can't be that arbitrary since I'll use the same every time. If I choose the point in function of the speed I may (or not) introduce a bias.

Do you know what people usually do to convert radius to angle? The angle is a simplification. Like a running football player can turn close to 90 degrees but a truck can't maybe the truck can turn at 15 degrees top. The football player has a smaller radius of rotation than the truck.

I could compute the angle one unit of time later (dependent of speed). I could normalize the speed first by computing the angle at a small distance (constant).

Please give your opinion
 
It is not at all clear what you want to do.

Is the point moving along a straight line, or a curved line (path)? You seem to be saying that the point is not really constrained to whatever "line" you refer to.

In your example, are you saying that the actual path of the point is the circle? (Your equation is missing something; did you mean (x-1)^2+y^2=2^2, which passes through (-1,0) but has radius 2 rather than 1 as you say?)

The quick answer to your question is that radius and angle are entirely independent. But without understanding the real nature of your problem, I can't be sure what radius and what angle you are trying to relate. Note that a truck can turn through any angle you can imagine -- it just takes longer to do it!
 
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