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 ...

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Friction is a force that exists when two surfaces rub up against each other. For example, this cup on ...

Wear has major impacts on everything from the bearing of a wind power plant to an artificial hip joint. However, the exact cause of wear is still unclear. Scientists now show that the effect occurs at ...

Some forces are called contact forces because they require objects to touch. One is tension force, found in stretched wires. Another is the force found in a spring. And last are resistive forces: ...