More wheels and axle

How many wheels are there on a bicycle? Two . wrong! There are there.Apart from the two big wheels, there is the small toothed wheel to which the pedals are attached. It is called the chain wheel because it moves the chain when you pedal. The chain wheel and pedal system is another example of that simple machine, the wheel and axle. When you pedal your bike, the pedals (acting as the wheel) turn in a large circle, while the chain wheel (acting as the axle) turns in a small circle.  This means that the you apply to the pedals turned into a bigger force at the chain wheel.

wheel machines

wheel from part of  hundreds of different machines, but they are not machines in themselves. A wheel become a machines when it is mounted on an axle.It become a simple machine called a wheel and axle. It is a machine because it can do work. A windlass is a kind of wheel and axle used to lift loads. For centuries it has been used to raise buckets from water wells. In the windlass (right), a rope car- rying the buckets of the water passes over an axle. The axle is turned by a wheel with a handle. When you turn the handle, yours hand moves in a large  circle, while the axle turns in a small circle. This action turns the small force you apply to the handle into a bigger force at the axle. This bigger force winds up the rope with its heavy load.

Wheels and axles

Ask your friends what they think is humankind's greatest invention, and make a note of what they choose. They might say for example, the laser ,the spade rocket, the sili-con chip, the computer or the television. But arguably it is none of these. It is something much simpler- the wheel. The invention of the wheel is thought to have taken place about 5,500 years old. Today, wheels in one from or another are found is most vehicles and engines an in other machines and gadgets of all kinds, from wristwatch- es to locomotives.

Classes of Levers

In the seesaw, the effort is applied on one side of the pivot to lift a load on the other side. This arrangement is typical of one kind of lever, called the first-class lever. In other classes of levers, the effort, pivot,and load life in different relative positions. In a second-class lever, the picot is located at one end. The effort is applied at the other end to lift a load in the middle. The wheelbarrow is a second -class lever. It has the pivot at one end and the load in the middle. A bottle-open-er is another second-class lever. Your forearm is an example of a third kind of lever, the third-class lever. It has the pivot at one end- the elbow. The load is held in the hand at the other end. The effort,which is supplied by the muscle in the arm, acts between.

Lots of Levers

The Lever is one of the six simple machines. It is indeed simple being just a straight rigid pole. Yet, it can still per- form useful work. A seesaw is an example of the simplest kind of lever. It consists of a long plank, which rests on a pivot in the mid- dle. If you sit on one end of the seesaw ,you exert a down- ward force,or effort on this end. The seesaw converts this effort into a force acting  upward at the other end of the plank. This upward force ca lift a friend sitting on that end. His or her weight from the load on the seesaw. In general: a lever rests on a pivot, also called a fulcrum. A force called the effort is applied at on point on the lever in order to overcome another force, the, load, at another. Usually, a lever in some way magnifies the effort to move a bigger load. The ratio of load to effort called the mechan- ical advantage. 

   

Simple Machines

In the Introduction, we gave the spade as an example of a simple machine. It hardly seems to be a machine at all,but it does have something in common with all machines- it help you perform a task -digging- more easily than you could without it.More technically, the spade increases force you put into the digging action. To turn over the soil, you push down on the handle. We call this force the effort. The spade is designed so that it magnifies this effort into a more pow- erful force, which lifts up a spadeful of soil (a weight called the load).The spade is an example of a kind of simple machine called the lever. In this chapter we look at the principles behind the lever and the five other kinds of devices scien- tists recognize as simple machines. They they are the inclined plane, the wedge, the screw, the wheel and axle, and the pulley . We also look at gears which we can think of a use- ful modifications of th wheel.

machine

Today we live in a world that is dominated by machines. in the home,machines vacuum the carpet,wash the dishes and launder the clothes. On the farm, machines plow the land ,sow the seeds, and reap the harvest. In industry, machines spin cloth, hammer metal in to shape, hoist up heavy loads and dig minerals out  the ground. In transportation, vehicles of every kind-- from bikes and cars to trucks and locomotives- transport us and our goods from place to place. Exactly what is a machine ? Scientists tell us that a machine is a device that  performs work. In a more popular sanse ,a machine is a device that help us carry out a particular task more easily and usually much faster. For example, it is difficult for us to till the soil with only our hands . It is much easier if we use a spade,A spade is a simple machine. It is even easier to till the soil if we use powered digging machine, like a rototiller, which has an engine that drives rotating blades. Usually, when we use in the book , we investigate some of the pernici- ples behind the machines we use. We also look at engines- the machines that drive other machines, and some typical machines at work . You can checks answers to the questions features throughout this book on pages 60-61.