The inside of old analog clocks is full of small cogs and gears that work with each other to turn the hands of the clock on the outside.

A cog is almost useless by itself, since it must have another cog to turn with in order to perform its main function.

A rollercoaster is often pulled up the first steep hill of its track with a cog, which pulls it forward by the metal protrusions on the bottom of the cars themselves.

A cog is sometimes referred to as a ‘cog-wheel,’ since cogs are really just wheels with teeth so they can grab and turn other cogs.

If you’ve ever seen the inside of a giant clock, such as Big Ben, then you have likely seen how a cog functions, and understand that it needs other cogs to do anything at all.