How to Estimate Your Car's Coefficient of Rolling Resistance
When two objects in contact with each other slide, a friction force develops resisting the motion. In classical physics, we distinguish between static friction (which resists the onset of motion as some force is applied) and kinetic friction (which resists movement after it has begun). You’ve noticed this before: the last time you tried to push a heavy box across the floor, say, you had to give it a push to get started and overcome the static friction (and if the static friction was great enough, it perhaps tipped over instead of sliding). When you stopped pushing, it didn’t continue sliding indefinitely; it gradually slowed and required some force to keep moving (although not as much as it took to get started). In both scenarios, your pushing on the box was required to overcome its static or kinetic friction. Upright, the fluid-filled can slides when pushed but as energy is dissipated due to friction with the table surface, it quickly comes to a stop. Cars are a bit more complicated b...