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  • 2 Post By FredWillpower
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September 17th, 2013, 04:45 AM   #1
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Resultant Force

I have a question I just cant seem to get my head around regarding resultant force using the triangle rule.

I donít know how to draw on this forum so I will try and explain

I have one force of 15n 35 deg from the horizontal pointing in a north east direction and another force 10n -20 from the horizontal pointing in at south west direction

hope that makes sense.

So how do I approach this?
has anyone got a method for resolving

Many thanks in anticipation
mrbronz is offline  
September 17th, 2013, 05:16 AM   #2
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Re: Resultant Force

You can approach this by resolving each force into its horizontal and vertical components using basic trigonometry. In this case, the horizontal forces will add together and the vertical forces will partially cancel out. In any case, this will leave you with net horizontal and vertical forces that can be combined into a net force at an angle again calculated by trig.

Alternatively, forces act like vectors, so you are effectively adding two vectors. Another approach, therefore, is to add one force/vector to the other by drawing the second force/vector beginning from the end of the first. The resulting sum of the two vectors represents the resulting force.
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September 17th, 2013, 05:27 AM   #3
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Re: Resultant Force

Hi there

Thanks for the reply.

Yes I got that and understand but still dont understand how to utilise the formula for this particula problem
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September 25th, 2015, 06:21 AM   #4
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RE: Resultant Force

OK, I'll try to explain this step by step:

First of all you need to draw a free-body diagram for the object you are studying.
In your case this means to draw an object subject to two forces:
The first of 15N making an angle of 35¬į with the horizontal (pointing north east)
The second of 10N making an angle of 20¬į with the horizontal (pointing south west)

The next step is to draw coordinate axes on your free-body diagram. In your case you can place the origin in the center of the object, the x axis horizontal and the y axis vertical.

Next you need to find the x and y components of the two forces (keep in mind that the components pointing in the negative directions of the x and y axes are negative)

As you have found the components of the two forces, you can find the x and y components of the resultant force by adding the x components, and the y components of the two forces.

After that, it is pretty simple to find the magnitude and direction of the resultant force:
For the magnitude you can apply Pythagoras' Theorem.

To find the direction, you first need to find the angle that the x component of the resultant force makes with the force itself, which you can easily do since the tangent of that angle is the ratio between the y and x component of the resultant force.

After you have found the angle that the x component makes with the force, it should be pretty simple to find the direction angle of the resultant force.

That's it!

Here's the full article that covers these steps in more detail, and gives you some examples: How to find the resultant force
Thanks from topsquark and mark eaton24

Last edited by FredWillpower; September 25th, 2015 at 06:39 AM.
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