Newton's Third Law
Forces come in pairs. When one object pushes or pulls another, the second object pushes or pulls back with the same size and the opposite direction. The pair always lives on two different bodies, which is the part most people get wrong on test day.
Two failure modes will trip you up. The first is mass asymmetry: students give the heavier or more active object the bigger force. They get the same force, every time. The second is treating an action-reaction pair as if it cancels out: it can't, because the two forces act on different bodies, never the same one.
The work
3 ways in · any order
Lesson
Newton's Third Law
›
Five sections of reading and worked examples (the on-by syntax, the swap test, the horse-and-cart paradox), then a ten-scenario applet that drills pair identification across collisions, contact, tension, and gravity at a distance.
Diagnostic
10-item topic check
›
Ten multiple-choice items that probe the partner-pair confusions: mass asymmetry, action-reaction misread as cancellation, gravity-and-normal mistaken for a third-law pair, and tension-pair errors at rope ends.
Targeted Practice
Drill a single misconception
›
Pick one of the failure modes you've missed and grind it on its own. The round is adaptive: two correct in a row clears the misconception and you move on.