Simple machines offer a mechanical advantage, however, the same amount of work is needed to perform the same job. The simple machine lessens the effort needed to do the same amount of work, making it appear to be easier. The payoff is that we may have to exert the lesser force over a greater distance.
There are six basic or simple machines, which alone or in combination make up most of the machines and mechanical devices we use. These simple machines are the lever, the pulley, the wheel and axle, the incline, the wedge, and the screw.
The logical order to introduce the six simple machines is that of the complexity involved in its usage, and how it complements or adds to the next machine. Thus, it makes sense to begin the unit by studying the incline as the most simple of the machines. All around in nature we are surrounded by inclines in the form of hills. The amount of work needed to elevate an object vertically is the same as the amount of work used in lifting the same object via an incline to the same place, but the force needed along the incline is much less. Some people do not consider the wedge as a simple machine because it may be seen as two inclines put together back to back. The wedge is discussed as a continuation of the incline and it is later compared to another of the simple machines: the screw.
The lever would be the next of the machines to be studied. Here a distinction between first, second, and third class levers is made. Samples are given for each of the lever types. This will be followed by the study of the axle and the wheel. In terms of the importance to the building of humanity, this machine must be one of the greater one in importance.
The pulley can be looked upon as a combination or a special case of the axle and the wheel, with the main difference being the inclusion of a groove in the wheel to allow the string to fit and rotate the wheel and axle when it is pulled. The study of different pulleys will demonstrate how by adding a couple of pulleys, a lesser force is needed to lift a weight.
Newton’s laws of motion
Prior to the study of the previous basic or simple machines, it is necessary to take a look at the laws of motion formulated by Isaac Newton (1642-1727). These laws are basic to the study of physics and therefore a necessity in a course on simple machines.
The first of these laws states that inertia is a “tendency of all objects and matter to stay still, or if moving, to continue in the same direction, unless acted on by some outside force.” Thus, in order to move an object at rest a force must be applied. The greater the object’s mass is the greater the force is needed to be applied. The force that is applied to an object times the distance the object is moved gives us the amount of work done (W=F*d). Therefore if there is no force applied there is no work involved.
Newton’s second law of motion describes how the force to move an object is equal to its mass times its acceleration (F=M*A). The third and last of the laws describes how for every action there is an equal and opposite reaction.
History of Simple Machines
It is difficult to pin point exactly the beginning or discovery of the basic or simple machines that have made possible the construction and building of entire civilizations. Nonetheless, we can simply observe the magnitude of the different architectural fits in the history of the humankind. We then understand that without basic machines such as the wheel and the axle, or the incline and the lever, civilizations such as the Egyptian, the Romans, and the Greeks could not have built their most admirable architectural landmarks such as the pyramids, the Roman Coliseum, or the many temples that remain as vestiges of ancient cultures. They also could not have conducted wars since the catapult made use of some of those simple machines such as the lever, wheel, and the ramp.
Although we still know little about the ancient Egyptian technology for handling the huge blocks of stone, there is no evidence they had knowledge of the pulley or the capstan (Boorstin, 1992). They mainly used sleds, rollers, and levers to move the blocks, and ramps or incline planes to raise the blocks into their place of rest.
Another tool used throughout history and also a sample of a universal invention in that it occurs in different parts of the world about the same time, is the plow. A sample of a wedge, the plow makes it possible to separate or break the soil in order to plant crops. Among other sample of universal inventions that are simple machines we have the ax, and the hoe.
Among the best know inventors throughout the history of human kind we must mention Archimedes and Leonardo daVinci. Archimedes, a predecessor to Leonardo, was the inventor of the Archimedes’ screw, a device used to lift water consisting of a spiral tube wrapped around an inclined rod.
A machine is a device that allows people to do work with less effort. Simple machines have few or no moving parts to them. These machines help us to move objects closer, apart, or to raise them to different levels by increasing the force or changing the direction of the force.
Machines offer us mechanical advantage by allowing us to use less force to do the same amount of work. The six simple machines are the incline, the wedge, the screw, the lever, the pulley, and the axle and wheel. Most machines in existence are considered complex machines because are composed of two or more of these simple machines.
The incline can be best described as a ramp or slanted surface, which decreases the amount of force needed to move an object to a higher level. Although the object travels a larger distance, it takes less effort force to move it.
There are many samples of inclines around us that facilitate the amount of work needed to move an object and that provide us with mechanical advantage. Without the use of the incline, the Egyptians would have been unable to build their pyramids. In the playground we find that the slide is an incline plane, the stairs to climb up and the ramp for the wheel chair are inclines too.
Shaped liked an incline plane, the wedge could be defined as that of a moving incline. In this case the effort force moves the incline forward while the object being moved (load) is pushed aside. It is easier to pry something open with a wedge once the point has been inserted in the opening than by attempting to pry it open with your hands.
Among the best-known samples of wedges are the nail, sewing needles, scissors, toothpicks, the ax, and different types of chisels. Even the zipper is a wedge.
The screw can be seen as an inclined plane wrapped around a cylinder with a grove in the center of it.
The advantage offered by the screw is that as it turns the rotary motion is converted into a forward or backward motion, which brings together or separates two objects. You need a much greater force to take apart two objects affixed with a screw. A sample of a screw in an everyday object is the lid of the peanut butter jar, or the inside of the pencil sharpener.
The lever is possibly one of the oldest simple machines in existence. The lever consists of a bar that turns around a point called the fulcrum. Levers are everywhere around us. Some samples of levers we do not think about include the doorknob, light switch, a stapler, a shovel, wheelbarrow, or our forearms.
There are three different kinds of levers according to where the fulcrum is in reference to the effort force (the work needed to move an object) and the load (the object being moved). The three different types of levers are: first-class lever, second-class lever, and third-class lever.
The first-class lever always has the fulcrum between the effort force and the load. The closer the fulcrum is to the load the less effort you need to make in order to move the object. The lever also changes the direction of force. Examples of first-class levers are the hammer when used to pull a nail out and a crow bar.
The second-class lever has the load between the fulcrum and the effort force. A wheel is the most important example of this type of lever. The closer the load to the fulcrum, the less effort is needed to move the object. A bottle opener is a good example of second-class lever.
In a third-class lever, the effort force is between the fulcrum and the load. This type of lever is the most inconvenient one in that no matter how far the load is from the fulcrum, the effort needed to lift the load needs to be greater than the load. A pair of twisters, forearm, and a rake are samples of this type of lever.
The axle and the wheel
The precursor to the axle and the wheel could be considered to be the roller or a long cylinder such as the trunk of a tree placed under the load. The wheel and the axle can also be described as a rolling incline plane. The advantage offered is that they remove friction thus making it easier to move a load with less effort. Of all the simple machines, it is possibly the most important of them all in that allows
A special type of the axle and the wheel is a gear. A gear consists of a wheel with teeth cut into it. Gears are used to change direction, control different things at once, and to slow or speed things up.
The pulley is a simple machine that consists of an axle and a wheel with a grove usually in the middle of it. There is no mechanical advantage to the use of a pulley. The advantage it offers is that of changing the direction of the force or effort we use to do the work.
There are three types of pulleys: fixed, movable and a combined pulley. The fixed pulley stays in place and does not move. An example of a fixed pulley is the one located at a flagpole in order to raise a flag. The movable pulley moves with the load. Among the better-known machines that make use of pulleys is the crane.