help with physics?

M

mattman

Well-Known Member
Anyone? how the hell do you know when to use sin or cosine when looking at vectors... like I know if they clearly show a 90 degree angle in there I can figure it out, but if not.. lost as fuck
 
MountainManGanjaGrower

MountainManGanjaGrower

Active Member
magnitude.jpgplease elaborate i might be able to help

like do you mean how can you use sine and cosine to find stuff? or just how is it related to vectors?


Like lets say the give you a vector with the Magnitude(length of hypotenuse normally), the x and y coordinate and no angle. To find the angle you would look at the definition of Sine and Cosine. You can use either. If x=4 and y=7 then the magnitude(length) will be the square root of 4^2+7^2 which is the square root of (65), lets just say ~8

with this information you can find the angle, the If you take the opposite over the hypotenuse- 7/8 you will get your sine representaion. Take the Sine^-1 of 7/8 and you will find your angle.

You could also take the adjacent over the hypotenuse for the cosine- 4/8 which is about 1/2. Since the unit circle has the cosine as the x coordinate you would look at 1/2 in the x direction of the unit circle and you would find this is about a 60 degree angle and the sine(Ycoordinate) would be (sqrt(3))/2 radians.

it's all about ratios...

haha sounds weird but if you have a certain problem you need help with its a lot easier just explaining it that way than trying to explain the relationships, mainly because there are a shit load of relationships between vectors and the unit circle(which is used to define sine, cosine, ets...).

haha St. Verde had it right with putting up a picture haha it's hard to write out.
 
Stride

Stride

Active Member
Use this. SOH CAH TOA

Use Sin when you have the measurements of Opposite and Hypotnuse. Use Cosine when you have the measurements of Adjacent and Hypotnuse. Then use Tangent if you have measurements of Opposite and Adjacent. All measurements are relative to the angle you are using to find the Vector. Does that make sense?
 
Sr. Verde

Sr. Verde

Well-Known Member
Stride said:
Use this. SOH CAH TOA

Use Sin when you have the measurements of Opposite and Hypotnuse. Use Cosine when you have the measurements of Adjacent and Hypotnuse. Then use Tangent if you have measurements of Opposite and Adjacent. All measurements are relative to the angle you are using to find the Vector. Does that make sense?
Click to expand...
This guy beat me to it.

Sine
opposite hypotenuse

Cosine
Adjacent Hypotenuse

Tangent
Opposite Adjacent



You basically determine what information you have, and according to the placement of that information in the triangle, you use sine,cosine, or tangent equations to find the missing information.



example
 
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