81 Let's Ride a Bike!-Mid

Let's Ride a Bike! FOCUS Question How do the parts of a bicycle work together to make it move and stop?

Early Bicycles Today's bicycles are complicated. They have gears, pulleys, wheels and axles, and levers. Bikes are designed for different surfaces. They are fast and comfortable, but bicycles were not always this way! Did you know that the first bike had no pedals? The rider had to straddle it and walk. It was called a walking machine. The velocipede (vuh-LOSS-uh) pead came later. The front wheel had an axle attached to the pedals. The rider pushed on the pedals to make the axle and wheels turn. Another name for this bike was the boneshaker. Its wooden wheels made for a bumpy ride!

The High-Wheel Bike A strange-looking bike replaced the velocipede. It had a gigantic front wheel. and a tiny rear wheel This was called the high-wheel bike. It was hard to ride and dangerous, too. The smallest bump could send riders flying headfirst onto the ground. Yet it was more popular than the velocipede. Why did people like it so much? The larger front wheel on the high-wheel bike worked better than the smaller front wheel on the velocipede. For each turn of the pedals, the larger wheel went farther. This made the high-wheel bike faster than the velocipede. Riders could go farther with the same amount of work. When someone makes an object move they are doing work.

The Drive Chain Makes It Go! Have you noticed that early bikes did not have chains? Many chains at that time were made of heavy metals. By the late 1800s, stronger and lighter metals had been made. This lighter metal was used to make an improvement to the bicycle. The drive chain was created. A drive chain is a pulley system with a chain that wraps around a gear. The gear, called a sprocket, has teeth to hold the chain as it turns.

The drive chain transfers energy from the pedals to the axle and rear wheel. Here is how it works. The pedals turn the sprocket at the front of the drive chain. This large sprocket moves the chain. The chain moves a smaller sprocket connected to the rear axle. The rear axle rotates, and the back wheel turns. The whole bike rolls forward. The large sprocket is similar to the high-wheel bike's large wheel. For every turn of the large sprocket, the rear sprocket turns faster because it is smaller.

Leverage! A lever is a stiff bar that turns around a point called the fulcrum. A kickstand is a lever that props up the bike. A handlebar is a lever that steers the bike. The pedals on a bike are also levers. The extra force gained by using a lever is called leverage (LEV-ur-ij). Levers, gears, wheels, and axles work together to make the bicycle move. When a rider pedals, energy moves through the bike. It moves from the pedals to the front sprocket, to the chain, to the rear sprocket, and to the rear wheel. The rear wheel moves the bike, which also makes the front wheel move.