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?

让我们骑自行车吧!自行车的各个部件是如何协同工作使其移动和停止的?

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!

今天的自行车很复杂。 它们有齿轮、滑轮、轮子、轴和杠杆。 自行车针对不同的路面设计。 自行车又快又舒服，但自行车并不总是这样的!你知道第一辆自行车是没有踏板的吗? 骑车人必须跨在上面走路。 它被称为行走机器。 后来出现了“velocipede (vuh-LOSS-uh)”。 前轮有一根连接在踏板上的轴。 骑车人踩踏板使车轴和车轮转动。 这种自行车的另一个名字是摇骨机。 它的木轮使它的行驶很颠簸!

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.

高轮自行车一辆外形奇特的自行车取代了自行车。 它有一个巨大的前轮。 和一个小后轮这被称为高轮自行车。 骑起来很困难，也很危险。 最小的碰撞都可能让骑手头朝下飞到地上。 然而，它比自行车更受欢迎。 为什么人们这么喜欢它? 高轮自行车上较大的前轮比自行车上较小的前轮工作得更好。 每踩一圈踏板，越大的轮子走得越远。 这使得高轮自行车比自行车快。 在同样的工作量下，骑行者可以走得更远。 当有人使物体移动时，他们是在做功。

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.

驱动链使它走!你注意到早期的自行车没有链条吗? 当时很多链子都是用重金属做的。 到了19世纪晚期，人们制造出了更坚固、更轻的金属。 这种较轻的金属被用来改进自行车。 驱动链创建完成。 传动链是一种带链的滑轮系统，它缠绕在齿轮上。 齿轮，称为链轮，有齿，以保持链条转动。

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.

驱动链将能量从踏板转移到车轴和后轮。 下面是它的工作原理。踏板带动传动链前面的链轮。 这个大链轮推动链条。 链条带动连接到后轴的一个较小的链轮。 后轴转动，后轮转动。 整个自行车向前滚动。 大链轮类似于高轮自行车的大轮子。 大链轮每转一圈，后链轮就转得更快，因为后链轮更小。

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.

利用!杠杆是一根硬棒，它围绕一个叫做支点的点转动。 支架是支撑自行车的杠杆。 车把是操纵自行车的杠杆。 自行车的踏板也是杠杆。 通过使用杠杆获得的额外力被称为杠杆(LEV-ur-ij)。 杠杆、齿轮、轮子和车轴共同作用使自行车运动。 当骑自行车的人踩踏板时，能量会通过自行车传递。 它从踏板移动到前链轮，到链条，到后链轮，然后到后轮。 后轮带动自行车，前轮也跟着动。