Mechanics 1: Resolving Forces - When to use Sin / Cos?

I'm currently doing Further maths - mechanics.

In the resolving forces part of the module, I just can't get my head around the idea of resolving forces.

MG Sin Feta (maybe spelt Theta, not sure)
or
MG Cos Feta?

Under what situation should i use sin, and what situation should i use Cos?

Cheers

//Andy

Reply 1

Tibbles168

Perpendicular to the plane : COS
Parallel to the plane : SIN

Reply 2

madsporkmurderer

The way I always remember it is if theta was 0 then would the force be acting entirely in the direction that you're resolving in (cos) or entirely perpendicular (sin)

Reply 3

Prokaryotic_crap

if the angle is inbetween 2 sides you use cos otherwise sin but havent done mechanics in a long time and wont do it ever again thank Allah

Reply 4

_lynx_

Um it depends if you are resolving forces vertically/perpenciular or horizontally/parallel to the plane. If you want to find the vertical component of the force, then you would use Mg sin theta. Horizontal- then Mg cos theta.

There may be exceptions, but i can't think of any at the moment.

Reply 5

Dr Salt

Just use soh cah toa. Actually, just use soh cah.

Reply 6

_lynx_

Ahha! like this. but i haven't come across this as I have not finished the exercise at school yet.

Reply 7

fieryiceissweet

i always remember it as cos horizontals better
then you know cos=horizontal and sin must be vertical
(thats about as good a mathematical sex joke youre going to get)