Whenever you move something, you are doing work. Lifting a pencil is a lot less work than lifting a desk. This is because you use less force, or strength, to lift the pencil.
            Force is not the only thing that is important in doing work. The distance, or how far, something is moved is also important.
            Some work needs a lot of force. And some work is done over a long distance. Because of these things, work can be hard for people to do. So, people may use machines. Machines are things which help make work easier.
            When people think of machines, they often think of cars or buses. But even a fork is a machine.

 

Simple Machines

            Machines are made up of just a few kinds of simple machines.
            One kind of simple machine is the inclined plane. Inclined planes let you use less force when you move something. One kind of inclined plane is a staircase. A hill is also a kind of inclined plane.
            The point on a tack is a simple machine. It is called a wedge. Wedges are used to push things apart. They may also be used to cut things. A knife is another kind of wedge. Other kinds of wedges are a fork, plow, and needle.
            A jar with a top you have to twist on and off is using another simple machine. The part of the top that holds it to the jar is a simple machine called a screw. Besides jar tops, there are other kinds of screws used to hold things together. Look at a door. Screws hold the door to the wall. The handle or knob is held on by screws. Screws can also be used to lift things. The seats of some chairs have screws. When the seat is turned, it may go up. Another way in which screws are used is to push or pull things. Propellers on boats are screws which push against the water. Propellers on airplanes are also screws.
            Imagine trying to lift a desk without even touching it. Do you think you can do it? You can, if you use a lever. A lever is another kind of simple machine. When using a lever, it is often helpful to think of it as having three parts. Somewhere between both ends of the lever is the fulcrum. The fulcrum is the point on which the lever rests. On both sides of the fulcrum, there is an “arm.” One arm has the load, or what you want to move. It is called the load arm. The other arm is the arm you force down. It is called the force arm. A seesaw is a type of lever, where the fulcrum is in between the force and the load. Some other levers have the load in between the force and the fulcrum. A wheelbarrow works like this. Another kind of lever has the force in between the fulcrum and the load. Tweezers work like this.
            Another simple machine is the wheel and axle. This machine is made up of a wheel and a rod. The rod is the axle. It is joined to the center of the wheel. The steering wheel on a car and handlebars on a bicycle are two kinds of wheel and axle machines. A doorknob is also a kind of wheel and axle. Sometimes the wheel on a wheel and axle has teeth. This kind of wheel is called a gear. A gear can also turn another gear. Gears are used this way inside of watches.
            When you use a lever, you use force in one direction. The load moves in another direction. Another simple machine works in this way. It is a pulley. A pulley is made up of a wheel and a rope. When you use a pulley, you use force in one direction. The load then moves in another direction. Many times it is hard to get at something to move it. For this reason, you might want to use a pulley. Pulleys can help raise flags on high poles. They can help lift things out of water. Most often, a pulley by itself cannot help you use less force to move something. But two pulleys can. Three, four, or even more pulleys can be used together to help make work still easier. Pulleys joined together in a certain way are known as a block and tackle.

 

Compound Machines

            All machines are made up of simple machines. Most machines you see and use every day are made up of two or more simple machines. These machines are called compound machines.
            One compound machine that you probably use is a pair of scissors. Scissors may seem simple. But one pair is made up of two levers. They are joined at the fulcrum. On each lever there is also a wedge used for cutting. Another compound machine is the pencil sharpener. It has wedges, screws, wheel and axles, and gears all working together.

 

Using Compound Machines

            Building and road workers have to dig down into the ground and move rocks and earth. They may use a bulldozer or a power shovel to do these things.
            Many compound machines are also used around homes and in parks. Each summer, grass is cut, trees are cut down, and bushes are moved and planted. In the fall, leaves may have to be taken away. In winter, snow and ice may have to be taken away from streets and sidewalks.
            Although compound machines can help people do work, they can also help people have fun. Machines are often used in sports. When people fish, they may use a fishing rod and reel. A fishing rod and reel is a compound machine. Bicycling and skiing are other sports in which compound machines are used.
            Many toys and games are also made of compound machines.

 

Lifting

            When you lift something, you use your force to lift against another force. That other force is called gravity. Gravity is the force which pulls things to the earth.
            When you drop your pencil, the force of gravity pulls it down. When you pick it up, you use your force to lift against gravity.
            People use many machines to work against gravity. Inclined planes, elevators, and even space rockets are such machines.

 

Pushing and Pulling

            One reason why you push and pull things is to start them moving. Things cannot move by themselves. All things will stay still until a force causes them to move.
            Just as a force is needed to start something moving, a force is needed to stop something from moving. So you may have to push or pull something to stop it from moving.
            Suppose you were to push or pull a box across the floor. The box would rub against the floor. This rubbing is called friction. It is friction which would make the box slow down and stop. To keep the box moving, you would have to keep pushing or pulling it.
            People have learned a way to get less friction when they push or pull things. They put loads on things that have wheels. Carts and wagons are such things.
            Friction can wear things away. Many machines have moving parts. As these parts move they rub against each other. Friction can wear away these parts of machines. People who use machines have learned another way to make less friction. They put oil on the moving parts of machines.
            Friction can be good. Riding a bicycle downhill and coming to a stop, you used your hand or foot to press the brakes. The brakes rubbed against the wheel. This rubbing caused friction which helped you stop. Pouring sand on icy roads causes friction when walking or driving a car.

 

Gasoline Engines

            Steam turbines are not used for driving a car or airplane. They are too heavy, and they take too long to “get up steam” and get ready to go. But there is another kind of engine that does not weight so much and that starts quickly. For cars and planes a gasoline engine works well. The energy of this engine comes from burning gasoline.
            When gasoline or any other fuel burns, it gives off hot gases and it heats up the air near it. If the fuel burns in some kind of container, the molecules of heated-up air and gases press on the sides of the container.
            Even the fire of a little match can make a powerful pressure.
            There are several cylinders in an engine, made of metal. The “stopper” is a round metal part called a piston. Each piston has a rod that is joined to a crank. Each piston is pushed by the pressure of hot gases from a gasoline fire.
            One after the other, gasoline fires keep popping and pushing against the pistons. A special part keeps mixing more gasoline and air to burn.
            The pressure of the hot gases gives the force to turn the wheels of a car or the propeller of an airplane.

 

Diesel Engines

            Some trucks, trains, and boats are run by diesel engines. A diesel engine is like a gasoline engine in most ways. Its heat energy comes from burning fuel, but it burns oil instead of gasoline. Diesel engines are good for pulling heavy loads.

 

Internal Combustion

            Gasoline and diesel engines burn their fuels inside themselves. Another word for inside is internal. Another word for burning is combustion. Engines that burn fuel inside themselves are called internal combustion engines.

 

Gas Turbine Engines

            Scientists have worked out a kind of heat engine that uses hot gases of a flame. In a gas turbine a liquid fuel is burned. The hot gases from the burning fuel have a great deal of force. They push against a turbine and make it turn. The gas turbine can do work by making a truck, locomotive, or ship move.
            Gas turbine engines are used in some airplanes. The engines turn propellers.

 

Electric Motors

            An electric motor has a wheel which is turned by an electric current. When electric current flows through a wire, the wire becomes a magnet. An electric current has energy.
            In every electric motor, there is an electromagnet. There is also an electric current to operate the electromagnet and something for the electromagnet to pull.
            Some motors have a part that starts and stops the electric current like a very quick touch and take-away.
            Many electric motors do not need such a part. Such electric motors work on a kind of electric current called A.C. this stands for alternating current. Alternating current acts like the touch and take-away. Alternating current makes the electromagnet of a motor go on and off.

 

Generators

            Electricity for homes and factories comes from machines called generators. When a generator is turned, electric current flows through wires to places near and far.
            Your electricity may come from a big generator many miles away. On a farm it may come from a small generator in the tool shed.
            In some places the force of flowing water turns a turbine. The turbine turns a generator. In other places a steam turbine does the work of turning the generator. Small farm or home generators are turned by gasoline or diesel engines.
            The important thing is that the generator does not have to be in the same place as the things which use the electrical energy.
            We do not have to build our factories, stores, or homes next to a river or a steam turbine. We can build them any place that suits us. We can string wires from the electric generator to the buildings where we use the electrical energy.
            The electric current turns the motors in our vacuum cleaners, electric refrigerators, and many other machines. It gives light and heat where we need them. Forces from far away supply energy where we need it.

 

Computers

            Machines can help people do many kinds of work. There is even a machine which can run other machines. This machine is called a computer.
            Computers can run the machines that make things. They can run machines that make clothes. Many books are made with the help of a computer.
            Though computers can run other machines, many people are needed to help run computers. Computer programmers are people who set up computers to do a certain kind of work. These people may “teach” a computer how to run other machines.
            Computer operators are people who run computers. They make sure a computer is working the way it should.