A child at a beach compares one sharp rock chip with one rounded grain through a magnifier.
a collision-history mystery

Which journey rounds a grain more?

mission started — follow each collision

Fresh chips are angular; many sand grains are rounded. Both the number of collisions and how hard they hit can change a grain.

clue 1

Many grains begin as sharp fragments

A sharp tan chip breaks from a rocky cliff and drops into a teal stream.

Weathering loosens fragments. Rivers and waves can carry them, and hard collisions knock off corners over time.

clue 2 · count contacts

Gentle knocks add up

Knocks0 gentle knocks
0 knocks4 knocks

Our made-up chip sheds one corner piece per gentle knock. Add contacts and count the loose pieces.

clue 3 · contact strength

One firm knock removes more

Contactgentle · 1 piece
gentlefirm

For this toy material, one gentle knock removes one piece; one firm knock removes two. Real grains do not follow fixed chip counts.

put the clues together

More knocks—or firmer knocks?

Identical toy chips travel equal distances. One meets five gentle contacts; the other meets three firm contacts. Their final chips are hidden.

Commit before the new setup runs.

Which journey removes more corner pieces?