I ain’t no Einstein. In terms of my smarts, I’m probably closer to Frankenstein.
While physicists discuss the speed of light, as a photographer I’m more comfortable discussing the speed of reflective light sources.
Reflective light sources such as cars moving, people walking/running, stuff moving in the wind. Even things that ain’t moving. When I’m the process of making a photograph, I view the speed of these reflective light sources as considerations of composition.
When considering the speed of reflective light sources, my shutter speed is the camera setting I’m paying attention to.