How a shaduf works · OakCrest Academy

🏺 How a shaduf works

A shaduf is a lever (a rigid bar that turns about a fixed point, the pivot). A long pole rests on a pivot pin high on two mud-brick pillars: a heavy lump of dried mud sits on the short end, and a bucket hangs from the long end on a rope.
Each side turns the pole with its weight multiplied by its distance from the pivot, a quantity called torque. In this model the 60 kg counterweight, 1 m from the pivot, gives 60 kg·m; the empty bucket and the pole together give only 14.1 kg·m.
So the operator must pull the empty bucket down, a pull of about 16 kg. The bucket sinks into the Nile and fills with 16 liters of water, and 16 liters of water weigh 16 kg.
Now the bucket side gives 58.9 kg·m, just less than the counterweight's 60. The counterweight wins, so it lifts the full bucket; the operator only guides it and tips it into the basin on the bank.
The water runs along a channel, through a sluice gate, into flat field basins. Egyptians of the New Kingdom painted this scene; the tomb of the sculptor Ipuy at Deir el-Medina (about 1250 BC) shows a shaduf watering a garden, and a Mesopotamian seal of roughly 2200 BC already shows one.

New words

lever: a rigid bar that turns about a fixed point; a seesaw is one
pivot (fulcrum): the fixed point about which a lever turns
counterweight: a weight placed to balance another weight
torque: the turning effect of a force: force multiplied by its distance from the pivot. Here weights are counted in kilograms to keep the arithmetic simple; scientists measure force in newtons (1 kg weighs about 9.8 newtons)
irrigation: bringing water to land by channels or machines, so that crops can grow
first-class lever: a lever with the pivot between the effort and the load

🏠 Try it for real

With a grown-up, balance a ruler on a pencil. Put two coins 5 cm from the pencil on one side; find where one coin must go on the other side to balance them. Predict first, then test: does weight × distance match on both sides?

💭 Talk about it

Explain it: why does the operator pull the empty bucket down rather than lift the full bucket up, when the total work is the same? In 2–4 sentences, say what the counterweight does and why that arrangement suits a human body. Then test a claim: someone says "a heavier counterweight is always better". Is that true? Use the counterweight slider as evidence.

Now explain it back: point at each part and say what it does.