Have you ever seen someone riding a unicycle? If you have, you probably remember it. A unicycle looks similar to a bicycle except that there's only one wheel and no handlebar. Although it's a skill that can take a while to master, anyone can learn to ride a unicycle.

No one knows for sure who invented the unicycle or when. Experts generally agree that the unicycle came about as a result of an early type of bicycle known as a “penny-farthing" (so-called because of its resemblance to the relative size difference between the British penny and farthing coins).

These early bicycles contained a rather large front wheel connected to a much smaller rear wheel. Legend has it that people riding penny-farthings eventually learned that they could lean forward and ride only on the front wheel.

Eventually someone removed the rear wheel and the unicycle was born.

Modern unicycles are like basic, less-complex bicycles. With only one wheel, unicycles have a seat, called a "saddle," which is connected via the seat post to the frame.

The frame sits atop the axle bearings, and the pedals directly control the movement of the wheel. This is different than regular bicycles that use a chain to transfer the energy of the pedals' motion to the wheels.

Unicycles are more difficult to ride than bicycles. Riders must maintain their balance from front to back, as well as side to side.

To get moving, riders must learn to “fall" in the direction they wish to go before correcting the fall by pedaling the unicycle to bring the single wheel back under their center of gravity.

As they move, riders must learn to control their center of gravity. If they “fall" forward, they can accelerate, while falling backward will enable them to decelerate as they correct their fall by once again bringing the wheel back directly under their center of gravity.

While this sounds simple enough, perfecting these techniques on a unicycle is another matter altogether! With only one wheel below you and no handlebars, learning the delicate balance required to ride a unicycle is a challenge for most people.

Although unicycles remain relatively rare, there are more unicycle riders today than ever before. Unicycles have even moved beyond the basic unicycle model most people have seen.

If you're into unicycle racing or unicycle basketball, you'll probably be interested in a sport unicycle. Of course, if you're a fan of rough, off-road terrain, then the mountain unicycle may be for you.

If you're a clown or a circus performer, a comical unicycle with a really small wheel may be just the ticket. Or, you could always go for the comic effect of the giraffe unicycle!

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Tomorrow in Wonderopolis we’ll find out what baseball cards, stamps, and dolls have in common!