Simple machines are a class of machines, typically with only one or two parts
There are two families of simple machines: the lever family and the wedge family. Simple machines in the lever family include levers, wheels and axles, and pulleys. Simple machines in the wedge family include wedges, inclined planes, and screws. The Greek scientist Archimedes originally made these classifications, over 2,000 years ago. Modern day machines are more complex and consist of many things other than just simple machines. However, simple machines are still very important to engineering and are widely used today.
Simple machines make work easier
In our everyday lives, we use the word work to describe many different efforts. In engineering and science, the mechanical definition of work is:
Work (W) = Force (F) * Distance (d)
The way you read this equation is, “Work is equal to force over a distance”. A force is a push or a pull. Doing mechanical work means that you are pushing or pulling something, which is another way of saying you are moving it. This equation captures the idea that you can move an object in different ways. You can use a greater force over a shorter distance. Or, you can use a smaller force over a longer distance. Simple machines let you change either the direction or amount of the force (or both) in the work equation.
The amount of force you apply to a simple machine compared to the amount of force produced by the machine is called mechanical advantage. Mechanical advantage is not always about getting more force out of a machine. The “advantage” exists because whether the machine requires more or less force than it produces, it makes the work at hand easier to complete.
Machines in the lever family all use rotation to create mechanical advantage
All of the simple machines in the lever family use some kind of rotation, or turning motion, around a point that supports the weight of the machine. The simple machines in the lever family are levers, wheels and axles, and pulleys.
The first simple machine in the lever family is the lever itself. A lever is used to move something, which is referred to as a load, using a pivot force. A lever consists of two parts, a bar that does the turning and a fulcrum, which is the point that supports the weight of the lever and the point on which it turns. You can use a long lever to lift a heavy load with a little amount of force, like lifting someone older and heavier than you on a seesaw. Or you can use a lever to create a great amount of force over a short distance, like using a hammer to pound a nail into piece of wood.
The second simple machine in the lever family is the wheel and axle. An axle is a long stick that attaches to the middle of the wheel. A wheel and axle can be used to make spinning the axle easier by increasing the size of the wheel. By increasing the size of the wheel, it is easier for the person applying the force to the wheel to make the wheel spin. This, in turn, makes the axle easier to spin. An example of a wheel and axle system is a doorknob. It is much easier to open a door with a doorknob than a stick coming out the door. Using a doorknob allows you to use a smaller amount of effort over a longer distance to open the door more easily. The wheel and axle on a car is also a type of wheel and axle system, but it works the opposite way a doorknob does. In the case of a car, the axle turns the wheel. The axle is a much smaller in size than the wheel, so the car needs a large amount of force, which it gets from the gas or electricity the car uses, to turn the axle, which then turns the wheel.
The last simple machine in the lever family is the pulley. The goal of a pulley is to raise, lower, or move a load horizontally, or side-to-side. Pulleys are made up of ropes and axles. The greater the number of ropes in a pulley, the greater the mechanical advantage provided by the pulley. Pulleys are typically used to lift heavy items. For example, pulleys are often used in elevators, creating the lift force to allow it to move up and down. Pulleys are also used in cranes to move containers on or off ships and to lift construction materials at building sites.
Machines in the wedge family use an angled surface to create mechanical advantage
All of the simple machines in the wedge family use an angled surface to make work easier. The simple machines in the wedge family are wedges, inclined planes, and screws.
The first simple machine in the wedge family is the wedge itself. One use of a wedge is to cut apart another object. Wedges use the point of an angled edge to separate the object when a force is applied to the opposite, or flat, side of the wedge. For example, think of cutting a sandwich with a knife. The sharp edge of the knife is the wedge, and you press that sharp edge down to cut. If you’ve ever tried to cut your food with the flat side of a knife, you know how much easier it is to use the wedge side. Another use for a wedge is to lift something slightly off the ground. For example, the ends of the forks on forklift machine are wedges, which allow the operator to push the forks under a heavy load to lift it off the ground.
The next member of the wedge family is the inclined plane. Inclined planes are used to get something to a higher height with less effort. This is done by increasing the distance the object is moved to get it to the new height. Instead of having to lift the object directly up, a person can push the object over a longer distance to get it to the new height. An example of an inclined plane is a ramp. It is much easier to roll a heavy box up a ramp than it is to lift it straight up.
The last member of the wedge family is the screw. Now, it might be harder to think of how a screw uses an angled surface, but it does too! Think about the curved ridge, or the thread, that wraps around the outside of a screw. If you were able to unwind that thread from the screw, you would have an inclined plane. Basically, a screw is just an inclined plane wrapped around a cylinder or a cone, depending on the type of screw. The screw uses the thread to change a twisting motion into a linear motion. Screws are believed to be the last simple machine that was created.
By combining simple machines, you create a compound machine
Simple machines are the building blocks of more complex machines. By using many simple machines in a compound machine, you can get an even better mechanical advantage. Compound machines can also accomplish more than a simple machine can on its own. A bicycle is a good example of a compound machine. It combines a pulley system of the bike chain with a wheel and axle simple machine in order to create the forward motion of the bike.