# Resolving Force-M1Watch

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#1
How do you know when to use sin instead of cos?
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2 years ago
#2
Sin vertical and cos horizontal.
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2 years ago
#3
(Original post by geography1294)
How do you know when to use sin instead of cos?
Well that is a massively ambiguous question. Do you mean in terms of right-angled triangles? In which case, I just look at the hypotenuse and see whether I have an angle between the hypotenuse and the side I want to find. If I do, then it's cosine, if I don't then it's sine. If I have two side lengths of the triangle, then it's tan.
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2 years ago
#4
Sin vertical and cos horizontal.
You can find vertical using cosine, and horizontal using sine as well. That's not much of an explanation.
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#5
(Original post by RDKGames)
Well that is a massively ambiguous question. Do you mean in terms of right-angled triangles? In which case, I just look at the hypotenuse and see whether I have an angle between the hypotenuse and the side I want to find. If I do, then it's cosine, if I don't then it's sine. If I have two side lengths of the triangle, then it's tan.
When you resolve forces, do you resolve in one direction and take whatever goes against the motion to be negative?
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2 years ago
#6
(Original post by RDKGames)
You can find vertical using cosine, and horizontal using sine as well. That's not much of an explanation.
I assumed he was asking when to use cos and sine when finding the horizontal and vertical components
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2 years ago
#7
(Original post by geography1294)
When you resolve forces, do you resolve in one direction and take whatever goes against the motion to be negative?
When you resolve forces, you are aiming to resolve them in 2 dimensions only (as far as M1 is concerned) such that they are perpendicular to each other - so no, you do not resolve in one direction. Why perpendicular? Because then they do not affect each other and you can treat them individually. And yes, you may take any forces going against the direction of motion as negative and then add that onto the driving force which would give the resultant forward force (assuming no external forces)
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#8
(Original post by RDKGames)
When you resolve forces, you are aiming to resolve them in 2 dimensions only (as far as M1 is concerned) such that they are perpendicular to each other - so no, you do not resolve in one direction. And yes, you may take any forces going against the direction of motion as negative and then add that onto the driving force which would give the resultant forward force (assuming no external forces)
So for a x and y coordinate grid, you would be resolving left to right and everything on the side of the negative coordinates would be against the motion?
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2 years ago
#9
(Original post by geography1294)
So for a x and y coordinate grid, you would be resolving left to right and everything on the side of the negative coordinates would be against the motion?
No, that isn't quite how it works. It also depends in which direction your object is moving. When an object is moving in 2 dimensions, you first resolve all the forces into the 2 perpendicular components, let's say horizontal and vertical. Now considering the motion horizontally, if it is moving to the right, then any forces acting to the left would be counted as negative if you wish, it just depends how you personally prefer it. I, for example, just take them as positive forces and simply subtract them from the driving force which is no different.
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2 years ago
#10
I assumed he was asking when to use cos and sine when finding the horizontal and vertical components
It's not always about finding horizontal and vertical components. Parallel and perpendicular force components to the plane would be a much more accurate saying.
1
2 years ago
#11
(Original post by RDKGames)
It's not always about finding horizontal and vertical components. Parallel and perpendicular force components to the plane would be a much more accurate saying.
True, would it be better if I used i and j instead of horizontal and vertical?
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#12
(Original post by RDKGames)
When you resolve forces, you are aiming to resolve them in 2 dimensions only (as far as M1 is concerned) such that they are perpendicular to each other - so no, you do not resolve in one direction. Why perpendicular? Because then they do not affect each other and you can treat them individually. And yes, you may take any forces going against the direction of motion as negative and then add that onto the driving force which would give the resultant forward force (assuming no external forces)
Also for resultant forces, how do you know which way to draw the force on the diagram?
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2 years ago
#13
(Original post by geography1294)
Also for resultant forces, how do you know which way to draw the force on the diagram?
The resultant force is always the one in the direction of motion.

If there is no motion, then the forces balance.
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2 years ago
#14
True, would it be better if I used i and j instead of horizontal and vertical?
The notion of and is that they are simply perpendicular vectors, but they do not specify how they are perpendicular. So you could indeed use them if you explain that is parallel to the plane, and that is perpendicular to it, or vice versa if you wish. Or you can say that one if horizontal and the other is vertical.
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2 years ago
#15
(Original post by RDKGames)
The notion of and is that they are simply perpendicular vectors, but they do not specify how they are perpendicular. So you could indeed use them if you explain that is parallel to the plane, and that is perpendicular to it, or vice versa if you wish. Or you can say that one if horizontal and the other is vertical.
Cool, thank you.
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