Final answer:
Gravity causes acceleration downhill due to the force component directed along the slope, similar to a perception of weight change when quickly descending in an elevator.
Step-by-step explanation:
When you are going downhill, gravity's pull will make you accelerate. This phenomenon occurs because gravity provides a component of force in the direction of the slope, which, when combined with any additional pushing force and surpassing the opposing force of friction, causes an object to accelerate downhill. This effect is similar to the sensation of weight change you might feel in a high-speed elevator when it accelerates downward, as described by Einstein. Additionally, as per Newton's first law, without sufficient opposing forces, an object in motion continues in motion along the same path unless acted upon by an external force.