How long did it last?

This lesson asks you to use units of time, such as seconds, minutes, hours and units you make up, to say how long different events last. The museum offers one old clock that marked time in half hours; the clocks, the timings and the units you make up your class brings. ¹

Think of a clap, a lunch and a school day. Say whether each is best told in seconds, minutes or hours, and why.

Count how many times you can bounce a ball before a minute passes, and use "one bounce" as a unit to tell how long something lasted.

Imagine a machine that tells you a half hour has passed. The Met's catalogue describes the elephant clock in al-Jazari's book: every half hour figures move, a ball drops and a sound is heard ². A ball passes from falcon to dragon to a vessel containing a gong, and counting accumulated balls indicates elapsed time ². The record adds that the elephant is a machine's shape in al-Jazari's book, and the picture a later copy, not a living animal or a photograph of his original clock ³.

This clock gives a signal that can be seen and heard every half hour. Why might that help someone who is busy with other work?

• The elephant clock: how its figures, balls and gong show a half hour.
• Al-Jazari: the author of the book in which the clock is described.

Read the record on the elephant clock. Drop a counter into a cup every time a half minute passes, and use the counters to say how long a short song lasts.