Gravity: The force that attracts objects towards each other, specifically towards the center of mass. On an incline, gravity pulls objects downwards.
Angle of inclination: The measure of how steeply an incline is angled in relation to the horizontal plane.
Normal force: The perpendicular force exerted by a surface to support the weight of an object resting on it. On an inclined plane, this force acts perpendicular to the plane's surface.