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This is probably a very simple question to all of you, but I have never taken a physics class, so I am lost for what I need to do for a programming problem. I will need to specify a force by inputting the newtons x, newtons y, and newtons z.

How can I calculate these 3 forces based on the desired angle and desired force for that direction?

Thank you for your time, this project is important to me.

Mike Spivey
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    @MattBell: Why don't you try physics.stackexchange.com –  Sep 30 '10 at 18:59
  • Thank you, I looked for a Physics stack but I guess I missed it. –  Sep 30 '10 at 19:00
  • How would the angle/direction for the force in three dimensions be given? – Isaac Sep 30 '10 at 19:07
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    @MattBell: So you mean to say that if there are no physics forums available you will post them into math... Common! –  Sep 30 '10 at 19:07
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    @MattBell: You can even try physics help forums. Moreover for your problem, i think Lami's theorem may help. Look at a good book on statics. –  Sep 30 '10 at 19:08
  • @MattBell: (1) Is your $x,y,z$ referential orthonormal? (2) Is the force given by let's say $\mathbf{F}=\frac{\left\vert \mathbf{F}\right\vert }{\left\vert \mathbf{v}\right\vert }\mathbf{v}$, where $\mathbf{v}$ is the vector $\mathbf{v}=v_{x}\mathbf{i}+v_{y}\mathbf{j}+v_{z}\mathbf{k}$ ? – Américo Tavares Sep 30 '10 at 20:37
  • If you are just given a magnitude and 1 angle that is enough information to uniquely specify a vector in 2 dimensions, but not 3. If you have 2 angles and a magnitude, you may want to look up spherical coordinates. – WWright Sep 30 '10 at 22:02
  • @MattBell: Further to my comment "(2) Is the force given by let's say $\mathbf{F}=\frac{\left\vert \mathbf{F}\right\vert }{\left\vert \mathbf{v}\right\vert }\mathbf{v}$, where $\mathbf{v}$ is the vector $\mathbf{v}=v_{x}\mathbf{i}+v_{y}\mathbf{j}+v_{z}\mathbf{k}$ ?" I would like to add that you can change from rectangular to cylindrical or spherical co-ordinates or vice-versa. – Américo Tavares Sep 30 '10 at 22:15

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Isaac's comment asking how the angles are given is a good one. If you specify that and the coordinate system the problem will be well posed. Guessing that it is in azimuth $(\phi )$ and elevation $(\theta )$, with $\phi =\theta =0$ along the positive x axis and positive z up, $F_x=F\cos(\theta )*\cos(\phi ), F_y=F\cos(\theta )*\sin(\phi ), F_z=F\sin(\theta )$

Ross Millikan
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