# The Naked Scientists Forum

### Author Topic: How do force vector diagrams work?  (Read 2015 times)

#### 1w2e3r4

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##### How do force vector diagrams work?
« on: 12/08/2012 13:00:33 »
Q: a force P acts on a body at an angle theta to a horizontal line OX. P, together with a pull of 1.5kN at 30 degrees to, and below, OX, has the same effect as a force of 5kN at 45 degrees to, and above, OX.

The following picture that I have drawn, it is corresponding to the questions?
« Last Edit: 13/08/2012 08:52:56 by chris »

#### CliffordK

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##### Re: Simple parallelogram of forces problems, help
« Reply #1 on: 12/08/2012 20:07:30 »
Unfortunately you don't seem to have any questions here.

TheNakedScientists isn't a place to have your homework done for you.

You did mention a parallelogram in the title.  When summing vectors, you can essentially redraw the vectors head to tail and the resultant vector is from the beginning of the first to the end of the last one.  It doesn't make any difference which order you draw the vectors, and thus you get a parallelogram.

I am a bit rusty on my Polar coordinate math

One option might be to convert your problem into Cartesian coordinates by considering the vectors as right triangles with the axes, then using the old
SOH CAH TOA
Sin(θ) = opposite over hypotenuse

In Cartesian coordinates, you can simply add all of the X components, and add all the Y components of the vectors.

#### imatfaal

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##### Re: How do force vector diagrams work?
« Reply #2 on: 14/08/2012 13:12:52 »
Further to Clifford's comments.  Arrows must point in the right direction - I am not sure from you description if this is the case. Normally we would draw the first stage diagram with all arrows leading from the object (remember push on one direction is pull from 180degrees around).   Importantly, the length of arrows should approximate the magnitude of the force - yours do not.

Then try rearranging the arrows such that forces which act together are linked head to tail.  So the two forces that act together should when added together lok like the third
« Last Edit: 14/08/2012 14:20:44 by imatfaal »

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##### Re: How do force vector diagrams work?
« Reply #2 on: 14/08/2012 13:12:52 »