On a flat horizontal surface, such diagrams are pretty straightforward showing that:
- Gravity exerts a downward force
- The surface exerts an equal and opposite upward force (the Normal force)
For objects on a ramp, the diagram can become cluttered and confusing fairly quickly. The key is to understand the fundamental concepts of gravity, friction, and applied forces. Each type of force when exerted upon the object can result in movement up or down the hill, as well as stop the object altogether. Additionally, an object moving up or down the inclined plane at a constant speed might exhibit an overall Net Force of 0 Newtons, but that does not mean that an external force need not apply. Free-body diagrams for objects on an incline must (at the minimum) depict:
- Gravity’s downward force and the corresponding translated downhill force parallel to the surface.
- The surface exerts a Normal force that is perpendicular to the surface and both equal and opposite to gravity’s perpendicular surface component.
- An Applied Force acts uphill/against the gradient.
Optionally, if the conditions exist, the free body diagram can also show:
- Static friction acts uphill/against the gradient.
- Kinetic friction can act either way depending on the desired motion of the object.
This inclined plane force calculator and problem solver helps solve the problem, while showing all the steps in the various calculations and displaying a fully labeled free body diagram.