#1 - Machines big and small 机器大小

1.Machines are everywhere!
They help us do things or make doing them easier. Every time you play on a see-saw, you are using a machine! A lever is a stiff bar that tilts at a point called the pivot or fulcrum. The pivot of the see-saw is in the middle. Using the see-saw as a lever a small person can lift a big person by sitting further from the pivot.

V A Pivot highlighted for you to see in the see-saw. V

2.The screw is another simple but useful scientific machine.
It is a ridge or thread wrapped around a bar or pole. It changes a small turning motion into a powerful pulling or lifting movement. Wood screws hold together furniture or shelves. A carjack lets you lift up a whole car.

V This is a screw! V

3.Where would you be without wheels?
Not going very far. The wheel is a simple machine, a circular disc that turns around its center on a bar called an axle. Wheels carry heavy weights easily. There are giant wheels on big trucks and trains and small wheels on rollerblades.

V That's a wheel right there. V

4.A pulley turns around, like a wheel.
It has a groove around its edge or a cable or rope. Lots of pulleys allow us to lift heavy weights easily. The pulleys on a tower crane can lift huge steel girders to the top of a skyscraper.

V This is a basic Pulley. V

5.A ramp is a simple machine called an inclined plane.
It is easier to walk up a ramp than to jump straight to the top.

V A ramp. V

6.Gears are like wheels, with pointed teeth around the edges.
They change a fast, weak turning force into slow, powerful one - or the other way around. On a bicycle, you can pedal the steepest hill in bottom (lowest) gear, then speed down the other side in top (highest) gear.

V These are gears in a bicycle. V

机器无处不在！
他们帮助我们做事情或使他们更容易。每次在跷跷板上玩耍时，都使用机器！杠杆是一个刚性杆，在称为枢轴或支点的点处倾斜。跷跷板的枢轴在中间。使用跷跷板作为一个杠杆，一个小人可以通过从枢轴坐下来抬起一个大个子。

V突出显示一个枢轴，让您在跷跷板上看到。 V

螺丝是另一种简单但有用的科学机器。
它是围绕酒吧或杆子的脊或线。它将一个小的转动运动变成一个强大的拉动或提升运动。木螺丝固定在家具或货架上。一辆劫车让你举起一辆整车。

V这是一个螺丝！ V

你会在哪里没有车轮？
不会很远车轮是一个简单的机器，一个圆盘，在一个称为车轴的酒吧中转。车轮轻松携带重物。大型卡车和火车上有巨大的轮子，以及溜冰鞋上的小轮子。

V那是一个轮子。 V

滑轮像车轮一样转动。
它的边缘有一个凹槽或一根电缆或绳索。许多滑轮允许我们轻松地提起重物。塔式起重机上的滑轮可以将巨大的钢梁提升到摩天大楼的顶部。

V这是一个基本的滑轮。 V

斜坡是称为倾斜平面的简单机器。
沿着斜坡比直接跳到顶部更容易。

V斜坡V

几何像轮子，边缘有尖齿。
他们将快速，微弱的转弯力转变成缓慢，强大的一个或另一个方向。在自行车上，您可以在底部（最低）档位踩下最陡峭的山丘，然后在顶部（最高）档位下降。

V这些是自行车上的齿轮。 V