ROSENFELD IMAGES LTD / SCIENCE PHOTO LIBRARY ROSENFELD IMAGES LTD / SCIENCE PHOTO LIBRARY
Cogs. Two large, steel cogs or gear wheels after manufacture. The cog at left has been attached to the chain of a pulley so that it can be lifted. The teeth of the cogs are spiralled around the rim. This type of cog is known as a helical gear and the design is particularly suitable for handling heavy loads. Cogs are used to transmit rotational motion from one shaft in a machine to another. The speed of rotation can be changed by connecting cogs with different numbers of teeth. If the driven cog has more teeth than the driving cog the speed will reduce. Photograph of a cog built for use in the gears of rolling mill machinery. Photographed in Germany.
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