The One Speed Everyone Agrees On
▶ DRILLThrow a ball from Vika's flying spaceship and George, on the ground, measures it going faster — the ship's speed adds to the throw, exactly like the skateboard drill. But when Vika shines a light, George measures it at exactly light-speedno matter how fast the ship is moving — the ship's speed simply does not add on. Light has one speed everyone agrees on, and that single stubborn fact is the rock the whole rest of relativity is built on. Use the Explain it for a kid / a grown-up switch to set the depth.
The big idea — light has one speed everyone agrees on, no matter who is moving or how fast. Balls (and everything else) pick up the speed of whatever throws them; light flat-out refuses. This one stubborn fact is the rock the rest of relativity stands on. (We drew the ball impossibly fast so you could see it — real balls are far, far slower than light.) How can light ignore the ship's speed? Speeds combine in a sneaky way — that's another drill. And because light won't bend, space and time have to instead — that's what the next drills show.