It's perhaps the second week of your introductory physics course. Your instructor starts talking about friction and writes the following two formulas on the board. Then there is probably some sort of ...

I'll be honest—friction is pretty complicated. Imagine that I have a block of wood sliding on a table. In some way, the atoms on the surface of the wood block are interacting with the surface atoms on ...

A force is a push or a pull. For example, when you push open a door you must apply a force to the door. You also must apply a force to pull open a drawer. You cannot see a force but often you can see ...

Friction is a force that opposes motion. It is present whenever two surfaces rub over each other, such as when you rub your hands together, or when you apply the brakes on a bike or in a car. Friction ...