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Grades K–2 · Machines

How does a matched toy key release a latch?

A little toy box can stay shut even when its lid is pulled. A small catch, called a latch, rests across the opening and blocks the lid's movement. Moving that catch out of the way lets the lid open.

A turning toy key draws a latch out of its catchTwo cutaways show a toy latch before and after a half-turn. The fitted key turns a short blue arm around the same fixed center. A pin on the arm fits inside a vertical slot in the orange latch. Turning the arm moves the pin left, drawing the guided latch out of the gray catch. The slot allows the pin's up-and-down movement during the turn. Both the joined mechanism and the released catch are visible.A small turn releases a lidThe key fits the turning part.Toy key1 The latch holdsTurning armCatchLatchThe key turns the blue arm.Its pin moves the latch left.2 The latch draws backTurning armCatchLatchThe latch is clear of the catch.Now the toy lid can open.Cutaway: one toy mechanism
The matched key turns an arm whose pin draws the sliding latch back. The two cutaways show the latch inside its catch and then clear of it.

In this toy mechanism, a shaped key fits a matching guide. Turning the key turns a small connected arm. A pin on the arm fits inside a long hole in the latch. As the arm turns, the pin draws the latch back, away from the catch.

The key does not pull the whole lid open. It moves the part that stops the lid from opening. Once the latch is clear, the lid can move.

This explains why a small turn can release a much larger moving part. The shapes must fit and the connected parts must be able to move. This is one simple toy latch; other kinds of locks use different arrangements inside.

About this explanation

Starting knowledge: Match simple shapes and recognize a part that holds a toy lid shut.

Sources

  • Science Museum Group — Iron lock, key and bolt, English, 18th century
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