The Science Behind a Bicycle: Wheels and Axels
Although they typically go unnoticed in everyday life, many tools we use to survive would not be possible without simple machines. The six simple machines, identified by Renaissance scientists, are the wheel and axle, pulley, lever, wedge, screw, and inclined plane. These machines are used to apply force to a single load. When two or more simple machines are used together, the result is called a compound machine.
One example of a common compound machine is the bicycle, which uses a system of wheels, levers, and pulleys. A bicycle is a compound machine used to transport one or more people using a frame attached to two wheels. When force is applied to its pedals, the energy is converted with a series of machines to forward motion. The most prominent element of a bicycle are its wheels. The word "bicycle" actually means "two wheels," and without these two wheels, a bike would remain motionless.
The wheel and axle is a simple machine that works by reducing friction in trying to move a load. The first wheel was believed to have been using around 7,000 years ago in Mesopotamia, although it would be another 1,000 years before the wheel was used in transportation. Before the use of wheels, large loads were transported on carts that slid along the ground, often dragged by animals. This was inefficient, as the friction created between the sled and the ground would absorb some of the pulling force, slowing it down. When a cart is attached to a wheel and axle, the friction is reduced. Friction still remains between the wheels and the ground as well as between the wheels and the axle, but the reduced friction makes moving the load easier.
Although the wheels on a bicycle reduce friction, a force still needs to be applied to the wheels of a bicycle to create motion. This force is applied to the wheels using a pulley. A pulley is a simple machine that creates a mechanical advantage and supports the changing of direction for a rope or cable. The pulley system used in a bicycle is referred to as a chain drive. Using force provided from the pedals, the chain drive pulley system transfers mechanical energy to the wheels. Once this energy is transferred to the wheels, the bicycle can move forward.
The force applied to the chain drive comes from the pedals of the bicycle. These pedals act as levers. A lever is a simple machine made of a flat bar, and it often rests on a pivot point called a fulcrum. In the case of a bicycle, the levers attached to the bike's pedals are pushed down to direct force into the pulley system.
Other simple machines are present on a bike as well. Screws are vital in its assembly, and without them, the bike would fall apart. A screw is an inclined plane wrapped around a central shaft. The inclined plane works as a wedge and assists in holding two separate pieces of the (bicycle) together. Screws are used in many other applications, such as construction, as a method to fasten two separate objects together.
The teeth on the gears that drive the chain through the pulley system act as wedges. Although wedges are often used to separate two items, in this case, they are used to apply force to the openings in the bicycle's chain. Another example of a wedge is an ax. The metal head of an ax is actually a wedge that is used to separate wood into smaller pieces.
The final simple machine is the inclined plane. Inclined planes are present on a bicycle as parts of other simple machines, such as the screw and wedge. Inclined planes are used to lift heavy objects. An inclined plane is a flat surface raised at an angle to reduce the amount of force needed to lift an object. Inclined planes are often seen on the backs of delivery trucks and used to help lift items into the back of the truck.
Simple machines are essential tools in modern life. By reducing the amount of force needed to move a load, simple machines make common tasks possible and in many cases much easier. Without these machines, we wouldn't have many of our common necessities. Even though many other machines have been discovered and invented in the time since the six simple machines were defined, the wheel and axle, lever, pulley, screw, wedge, and inclined plane are still the building blocks on which all other machines have been based.