A slow-rolling steel ball can launch another ball fast enough to blur in a photo. The trick is a magnetic chain reaction, where each step adds energy to the next. Tape four strong magnets along a grooved ruler and place two steel balls to the right of each magnet. Roll one ball slowly toward the first magnet. It snaps in, transferring energy through the group — and the last ball shoots toward the next magnet even faster. Each magnet in the line adds energy to the next ball, so speed builds at every stage. The final ball fires off the end of the ruler and hits a target hard.

The spacing between dominoes controls how fast a topple travels — and closer is not always faster. Line up 100 dominoes at seven different gaps ranging from 10 mm to 40 mm, knock over the first tile, and time the full chain. Speed peaks at a 30 mm gap and drops on both sides. Too close, and each falling tile barely reaches the next. Too far apart, and each tile loses too much energy before triggering the one ahead. When each step needs just the right distance to trigger the next one, the chain runs fastest.