Final answer:
The concept of relative motion explains how different observers perceive the motion of objects differently, such as a bicyclist seeing a stationary observer as moving in the opposite direction, and a sidewalk observer perceiving someone running alongside an ambulance as moving quickly.
Step-by-step explanation:
When passing bicyclists at speeds greater than 35 mph, it's important to understand the concept of relative motion in physics. If you were standing on a sidewalk and observed a bicyclist passing by, the bicyclist would perceive you as moving in the direction opposite to their motion. This is because from the bicyclist's frame of reference, they are stationary, and everything else is moving relative to them.
Similarly, when you're running alongside a moving object, such as an ambulance, you're stationary with respect to the ambulance but moving at a greater pace to an observer on the sidewalk due to the fact that you are moving at the sum of your velocity and the ambulance's velocity. When driving and attempting to overtake a slower vehicle, which is going below the speed limit, this same principle of relative motion applies. The vehicle you're passing is at rest relative to your own vehicle once you match its speed just before the overtake; it will then appear to move backward relative to you as you speed up to pass.