Two words that mean something specific in physics
In everyday language, “work” means your job and “energy” means how awake you feel. In physics, both words have precise definitions.
Work is done when a force moves something over a distance: W = F × d. If you push a wall as hard as you can but it doesn’t move, you’ve technically done zero work — even though you’re exhausted.
Energy is the capacity to do work. It comes in many forms: kinetic (motion), potential (stored, like a stretched spring or something held up high), thermal, chemical, and more.
The big rule: energy is never created or destroyed
This is the law of conservation of energy — one of the most important ideas in all of physics. Energy just changes form. A ball dropped from a height converts stored (potential) energy into motion (kinetic) energy as it falls.
Why this matters
Every engine, every meal you eat, every phone battery is really just a story about energy changing from one form into another, a little less useful each time (some is always “lost” as heat).