Px = P cos θx equation question.

[AcousticBruce]

$$P_x = P cos θ_x$$

is Px always the adjacent line of the triangle?

 

[RTW69]

Yes, if the adjacent side is of a right triangle, where P is the hypotenuse and θ is the angle between the Hypotenuse and adjacent side.

 

[AcousticBruce]

Thank you. And a new question.

Why would it be Px for adjacent and on the other side be P without a subscript?

 

[gneill]

Thank you. And a new question.

Why would it be Px for adjacent and on the other side be P without a subscript?

Presumably a vector of magnitude P is being decomposed into its X and Y components, with θ_x being the angle between P and the X axis. Thus:

Px = P cos(θx)

and

Py = P sin(θx)

 

[RTW69]

Your problem tells me that P_x is the component of P in the x-direction. The component of P in the y-direction would be labeled P_y. P is the hypotenuse. P might be a force at some angle θ from the x-axis and you are trying to find the component of that force in the x-direction which utilizes the Cosine trig function. If you were trying to find component of the force in the y-direction, P_y you would use the sine trig function.

 

[AcousticBruce]

So would you ever really have the θy?

 

[RTW69]

Yes, look at gneil's image. θ_x is measured from the x-axis. θ_y would be the angle measured from the y-axis and would equal 90 degrees- θ_x.

 

[gneill]

So would you ever really have the θy?

Sure. You never know which angle may be given to you or which one might be determined by some other factor in the problem. Example: problems that specify angles for pendulum strings which reference the vertical direction, not the horizontal.

 

[AcousticBruce]

Thanks a lot guys. Really! I am in a self study of physics and trigonometry. I am studying electronics and it seems that physics and trig would be a good thing to learn. :)