A bicycle, or bike, is a human-powered, two-wheeled, steerable vehicle that millions of people worldwide ride for sport (called cycling), recreation, and transportation. It is the most efficient means yet devised of converting human energy into motion. A bicycle consists of a seat, handlebars for steering, and pedals attached to the frame by which a person rides. It is the most common mode of transportation in the world, and is used by people of all ages and from all walks of life.
The first bicycles were invented in the early 1800s. A German inventor named Karl Drais designed the first two-wheeled machine that could be steered by turning the handlebars. Drais’ machine was called a draisine, a lauf-maschine, or running machine, but later manufacturers gave it the more practical name of bicycle. Early models had solid iron wheels without treads, which made them noisy and difficult to ride on country roads. Later, metal hubs were fitted with rubber tires, and the resulting machines were quieter but still rough riders. The modern bicycle owes its smoother ride to the Scottish inventor John Boyd Dunlop’s re-invention of pneumatic or “air” tires in 1888.
By the late 1800s, inventors had developed many other improvements that made the bicycle more comfortable and practical to ride. These included a chain drive, which transmitted power from the rider’s feet to the bicycle’s rear wheel, making it possible to travel at up to 16-24 km (10-15 miles) per hour—about four to five times as fast as walking. In addition, gearing systems were created that enabled the bicycle to travel up hills with less effort than pedaling alone.
Safety features include hand brakes and a freewheel, which prevents the back wheel from spinning when the rider is not pushing on the pedals. More recently, suspension seat posts and springs have been added to make riding more comfortable. Despite these improvements, thousands of people are injured in bicycle accidents each year and hundreds die. Injuries are most frequent in competitive cyclists and people who use bicycles for long distances on a regular basis.
To write a literature review, it is important to understand what type of information you are trying to gather and to organize your sources accordingly. A good approach is to examine the major themes in your research and write your review according to those themes. For example, if you are writing about whaling, you might organize your sources into sections that cover specific eras in the history of whaling and then compare those eras to each other. This will help you develop your arguments more effectively and make your review easier to read. You can also organize your sources into categories based on their perspective or opinions. However you organize your sources, the literature review should present a balanced, critical analysis of the current state of knowledge on your subject area.