When an object sits on a frictionless incline plane, the two forces acting on the object are the gravitational pull of the earth, its weight, **mg**, and the supporting force supplied by the surface of the incline, the normal, . These forces are shown in blue.
Since the object slides along the surface of the incline, we need to use the components of its weight, **mg**, when working problems. The formula used to calculate the component of the weight which acts parallel to the incline's surface is
F_{d} = mg sin(θ)
In this formula, you can use the mnemonic that the "d" represents "down" which is parallel to the incline.
While the formula used to calculate the component of the weight that acts
perpendicular to the incline's surface is
F_{n} = mg cos(θ)
In this formula, you can use the mnemonic that the "n" represents "normal" which is perpendicular to the incline. Let's take a moment and practice using these two preliminary formulas. |