In Progress
Skill 1 of 11
In Progress


Mom throws an orange to the kid. He catches it and puts in the grocery basket dad is carrying. They are affecting the objects; creating, stopping and preventing motion.

That takes some effort. Let’s invent a name for such effort: force with the symbol $\vec F$, with an arrow because a force naturally has direction (you can push and pull in different directions).1

Many, many, many forces exist in our world. Forces in strings hold up lamps, friction forces stop the gliding football player, a bridge holds up cars with a force. If the forces were not strong enough, the string would break, the football player would glide much farther (as on ice) and the cars would fall through the bridge.

You can feel several forces at once, of course. In the library there might be a fight over a book, with people pulling towards either side to try to wrestle it free. We could draw a simple sketch over which forces the book feels:

Two pulling forces and also the book’s weight, which naturally pulls downwards. Let’s call this drawing with forces as arrows a force diagram.