The modern world is rich with examples of complex machines whose workings are seldom understood. Students often believe that all machines produce much more work than their human operators put in. This view is consistent with their experiences of most powered mechanical devices e. Although most students will have common experiences of the use of simple machines like levers and pulleys, few will have any understanding of why their design may provide an advantage or how they should be best employed.
Many students also have difficulty in identifying or explaining these experiences to others and rarely identify parts of the human body, such as the arms or legs, as composed of levers.
The word machine has origins in both the Greek and Roman languages. The basic purpose for which most simple machines are designed is to reduce the effort force required to perform a simple task. To achieve this, the force applied must act over a longer distance or period of time resulting in the same amount of work being performed by a smaller force. Screws, levers and inclined planes are designed to increase the distance over which the reduced force acts so that we can push or pull with less effort.
Consists of a stiff beam that rotates around a fixed pivot point fulcrum located somewhere along the beam. Motion at one end of the beam results in motion at the other end in the opposite direction. The location of the fulcrum can magnify or reduce the force applied at one end at the expense or advantage of the distance over which the other end travels.
It is often used to split, cut or raise heavy objects depending on the angle of the sides of the wedge. Combines a wheel with a central fixed axle which ensures that both must rotate together. A small force applied at the edge of the wheel is converted by rotation to a more powerful force at the smaller axle.
This effect can be reversed by applying a large force to the smaller axle resulting in a smaller force at the edge of the larger wheel with much greater rotational speed. The rotation of a threaded shaft can be converted into movement in either direction along the axis of rotation depending on the direction of its spiral thread.
According to Bob Williams, a professor in the department of mechanical engineering at the Russ College of Engineering and Technology at Ohio University, an inclined plane is a way of lifting a load that would be too heavy to lift straight up.
The angle the steepness of the inclined plane determines how much effort is needed to raise the weight. The steeper the ramp, the more effort is required. That means that if we lift our lb. If we were to use an 8-foot 2. If we want to lift that same lb. This would let us pull down instead of up on the rope, but it still requires lbs.
However, if we were to use two pulleys — one attached to the overhead beam, and the other attached to the weight — and we were to attach one end of the rope to the beam, run it through the pulley on the weight and then through the pulley on the beam, we would only have to pull on the rope with 50 lbs. Again, we have traded increased distance for decreased force. If we want to use even less force over an even greater distance, we can use a block and tackle.
According to course materials from the University of South Carolina, "A block and tackle is a combination of pulleys which reduces the amount of force required to lift something. The trade-off is that a longer length of rope is required for a block and tackle to move something the same distance. As simple as pulleys are, they are still finding use in the most advanced new machines.
For example, the Hangprinter , a 3D printer that can build furniture-sized objects, employs a system of wires and computer-controlled pulleys anchored to the walls, floor, and ceiling. Many devices use screws to exert a force that is much greater than the force used to turn the screw. These devices include bench vices and lug nuts on automobile wheels. They gain a mechanical advantage not only from the screw itself but also, in many cases, from the leverage of a long handle used to turn the screw.
According to the New Mexico Institute of Mining and Technology, "Wedges are moving inclined planes that are driven under loads to lift, or into a load to split or separate. For example, if we want to split a log, we can drive a wedge downward into the end of the log with great force using a sledgehammer, and the wedge will redirect this force outward, causing the wood to split.
Another example is a doorstop, where the force used to push it under the edge of the door is transferred downward, resulting in frictional force that resists sliding across the floor.
Compound machine: A machine consisting of two or more simple machines. Fulcrum: The point or support on which a lever turns. Work: Transfer of energy by a force acting to move matter. The beauty of simple machines is seen in the way they are used as extensions of our own muscles, as well as in how they can redirect or magnify the strength and force of an individual.
They do this by increasing the efficiency of our work, as well as by what is called a mechanical advantage. A mechanical advantage occurs when a simple machine takes a small "input" force our own muscle power and increases the magnitude of the "output" force.
A good example of this is when a person uses a small input force on a jack handle and produces an output force large enough to easily lift one end of an automobile. The efficiency and advantage produced by such a simple device can be amazing, and it was with such simple machines that the rock statues of Easter Island, the stone pillars of Stonehenge, and the Great Pyramids of Egypt were constructed. Some of the known accomplishments of these early users of simple machines are truly amazing.
For example, we have evidence that the builders of the pyramids moved limestone blocks weighing between 2 and 70 tons 1. One of the keys to understanding how a simple machine makes things easier is to realize that the amount of work a machine can do is equal to the force used, multiplied by the distance that the machine moves or lifts the object.
In other words, we can multiply the force we are able to exert if we increase the distance. For example, the longer the inclined plane—which is basically a ramp—the smaller the force needed to move an object.
Picture having to lift a heavy box straight up off the ground and place it on a high self. If the box is too heavy for us to pick up, we can build a ramp an inclined plane and push it up. Common sense tells us that the steeper or shorter the ramp, the harder it is to push the object to the top. Yet the longer and less steep it is, the easier it is to move the box, little by little.
Therefore, if we are not in a hurry like the pyramid builders , we can take our time and push it slowly up the long ramp to the top of the shelf. Understanding this allows us also to understand that simple machines involve what is called a "trade-off.
So although we have to use less force to move a heavy object up a ramp, we have increased the distance we have to move it because a ramp is not the shortest distance between two points. Most primitive people were happy to make this trade-off since it often meant being able to move something that they otherwise could not have moved.
Today, most machines are complicated and use several different elements like ball bearings or gears to do their work. However, when we look at them closely and understand their parts, we usually see that despite their complexity they are basically just two or more simple machines working together.
These are called compound machines. Although some people say that there are less than six simple machines since a wedge can be considered an inclined plane that is moving, or a pulley is a lever that rotates around a fixed point , most authorities agree that there are in fact six types of simple machines. A lever is a stiff bar or rod that rests on a support called a fulcrum pronounced FULL-krum and which lifts or moves something. This may be one of the earliest simple machines, because any large, strong stick would have worked as a lever.
Pick up a stick, wedge it under one edge of a rock, and push down and you have used a lever. Downward motion on one end results in upward motion on the other. Anything that pries something loose is also a lever, such as a crow bar or the claw end of a hammer. There are three types or classes of levers.
A first-class lever has the fulcrum or pivot point located near the middle of the tool and what it is moving called the resistance force. A pair of scissors and a seesaw are good examples.
A second-class lever has the resistance force located between the fulcrum and the end of the lever where the effort force is being made. Typical examples of this are a wheelbarrow, nutcracker, and a bottle opener. A third-class lever has the effort force being applied between the fulcrum and the resistance force. Tweezers, ice tongs, and shovels are good examples. When you use a shovel, you hold one end steady to act as a fulcrum, and you use your other hand to pull up on a load of dirt.
The second hand is the effort force, and the dirt being picked up is. This man is demonstrating the use of a lever the board and fulcrum. Reproduced by permission of Photo Researchers, Inc.
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