ROSENFELD IMAGES LTD / SCIENCE PHOTO LIBRARY ROSENFELD IMAGES LTD / SCIENCE PHOTO LIBRARY
Cogs. Cogs in a gearing system. A cog with its teeth cut parallel to its axis is also known as a spur gear. 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. In the gear shown here, the central cog will rotate more quickly than the outer one because it has fewer teeth.
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