The Bicycle, Gears, and Fuel

The Bicycle

Before we start talking about Bicycles lets try an activity. I want you to take out a piece of paper and try and draw a working bicycle from memory. A bicycle is something we see all the time. It seems simple yet it is hard to draw.

The Evolution of the Bicycle

First we have the Dandy Horse

The Dandy Horse had no pedals. You simply pushed or walked with your feet. This seems simple to us now but before the invention of the bicycle this seemed like a good idea. It was a way to walk and sit down at the same time. And going down hill was fun.

Next we get the Velocipede

The velocipede had pedals on the front wheel. This was the first pedaled bicycle.

Then came the Penny Farthing also known as the Ordinary Bicycle

The Penny Farthing had a large front wheel and a small rear wheel. The large front wheel allowed a person to get a larger distance for their small pedal.

The Penny Farthing was dangerous because you sat so high off the ground

How to get on a Penny Farthing

Penny Farthing Crash

There were some safer designs by adding extra wheels but they became slow and hard to pedal

Eventually the Safety Bike was invented. It was called the Safety bike because it was comparing itself to the Penny farthing

By adding a gear and a chain both tires could be made the same size

In a penny-farthing bicycle, the pedals and the front wheel are directly connected just like they are on a kid's tricycle. That means that when you turn the pedals one time, the wheel goes around one time. That's an inexpensive way to build a bicycle, but it has a problem. Think about a kid's tricycle. The front wheel might be 16 inches (40 cm) in diameter, or 16 * 3.14 = 50 inches (127 cm) in circumference. That means that each time a kid on a tricycle pedals through one revolution of the front wheel, the tricycle moves forward 50 inches (127 cm). Let's say that the kid is turning the front wheel at 60 rpm, or one revolution per second. That means that the tricycle is moving forward 50 inches per second. That is only 2.8 miles per hour (4.5 kph). If the kid pedals twice as fast, at 120 rpm, the trike is moving at just over 5 miles per hour (9 kph), and the kid looks like his legs are about to spin off because 120 rpm is a lot of pedaling!

If an adult wants to ride a tricycle at a reasonable speed, maybe 15 mph (24 kph), and if the adult does not want his or her legs to fly off, then the tricycle's front wheel has to be pretty big. If the adult wants to pedal at 60 rpm, the front wheel needs to be 84 inches in diameter -- that's 7 feet (more than 2 meters) in diameter!

The first thing that causes bicycles to have gears is the fact that gears can reduce the wheel size from 7 feet in diameter to something reasonable. For example, if you put a gear with 42 teeth on the front chain wheel and a smaller gear with 14 teeth on the rear wheel, you have a 3-to-1 gear ratio. Now the back wheel can be 84 inches / 3 = 28 inches (71 cm) in diameter -- about the size of a normal bicycle wheel. This is a much safer approach.

The "lowest" gear ratio on the bike might be a front chain wheel with 22 teeth and a rear gear having 30 teeth. That means that the gear ratio is 0.73-to-1. For each pedal stroke, the rear wheel turns 0.73 times. In other words, for each pedal stroke, the bike moves forward about 60 inches (about 3.4 mph / 5.4 kph at a 60-rpm pedaling rate). The "highest" gear ratio on the bike might be a front chain wheel with 44 teeth and a rear gear having 11 teeth. That creates a 4-to-1 gear ratio. With 26-inch wheels, the bike moves forward 326 inches with each pedal stroke. At a 60-rpm pedaling rate, the speed of the bike is 18.5 mph (30 kph). By doubling the pedaling rate to 120 rpm, the bike has a maximum speed of 37 mph (60 kph). A range of 3.4 mph to 37 mph is fantastic, and it lets the rider climb the steepest hill very slowly or race almost as fast as a car! That is why a bike has gears.

History of a Bicycle

Parts of a bicycle

Fuel

Fuel is anything that can release energy

In groups of 4 I want you to write on post-its as many types of fuel you can think of.

Class Discussion:

Where does coal come from?

Where does oil come from?

Where does gasoline come from?