ASK YOUR SCIENCE TEACHER

May 20, 2023

QUESTION: How does a zipper work?

ANSWER: The zipper is so common and has been around for so long, we don't give much thought to where it came from or how it works. It is one of those devices that is not absolutely necessary but is one of the most useful devices in everyday life. It's much easier and faster to close a suitcase, back of a dress, coats, pants fly and sleeping bags compared to using buttons or cords. The zipper is so effective and reliable it has been the standard fastener for over 100 years.

The zipper was patented in 1893 by Whitcomb Judson as a method to fasten boots. The Navy bought Judson's patent in 1918 to secure flying suits. His invention was given the name zipper in 1926.

The zipper is an excellent example of a simple machine. All machines, implements, tools, and instruments, are made up of six simple machines: lever, pulley, wheel and axle, inclined plane, wedge and screw. The zipper makes use of the wedge plus a hook. A wedge is an object with an inclined surface. If you push a wedge forward, it will push an object to the side, perpendicular to the direction the wedge is moving. A door stop and plow are examples of a wedge. A wedge is used to split wood.

A hook is a curved piece of material that can be used to grab onto another piece of material. Think of a crochet hook. A zipper is made of dozens of teeth, and each has a hook and a hollow. The job is to latch every hook on each of the two tracts into a hollow on the opposite side. That latching mechanism is the slide that contains wedges that either force the interlocking teeth together or force them apart.

Each tooth has a small knob or protrusion on its top face and a hollow on its bottom. Teeth on the opposite sides of the zipper are staggered so that the protrusion of one fits into the hollow of the opposite tooth on the adjoining side. Some plastic zippers use two intermeshing spirals instead of two rows of teeth.

The teeth are built so that they can only be opened or closed one at a time. The slide is necessary to pull the teeth apart or put them together. When the zipper is opened, the upper wedge forces the teeth apart one at a time. When the zipper is closed, the interlocking teeth are forced together so they intermesh.

Whitcomb Judson (1843-1909) led a full and interesting life. Born in Chicago, Judson enlisted in the Union Army in 1861 and served in the 42nd Illinois Infantry Regiment. After the Civil War, Judson attended Knox College in Galesburg, Illinois, and became a salesman for agriculture equipment.

Judson began concentrating on railway systems that ran on urban streets. The first 14 of his 30 patents were for the railroad/streetcar. The first application for his newly invented zipper was as a shoe fastener to relieve the tedium of fastening high button boots that were fashionable at the time. Soon after, zippers were put on rubber galoshes, gloves, and tobacco pouches.

Judson married Annie Martin in 1874 and they had three children. In 1906, he and his wife moved from New York City to Muskegon, Michigan, to retire.

Scheckel

Larry Scheckel is a retired Tomah High School physics teacher.

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