Why are wedges and screws inclined planes

The inclined plane. The key idea here is that less effort is needed if a load is transferred over a long ramp or inclined path, as opposed to lifting it directly over a vertical path. For example, you may have noticed how movers move very heavy objects, such as a piano, into the back of their moving truck.

Obviously, they cannot easily lift such a heavy piece of furniture directly up and into the back of their truck. Instead, they use a long ramp — or inclined plane — to complete the job. This idea was used long ago by the ancient Egyptians: they used the inclined plane and human strength to erect monumental structures to amazing heights.

Even today, engineers employ the inclined plane in many other applications in order to accomplish seemingly impossible tasks. Just a few of these examples include wheelchair ramps, escalators, stairs, highways and even hiking trails, which all rely on the inclined plane as a means of raising heavy objects more easily. In addition to lifting heavy objects, engineers are also interested in splitting or separating material with as little effort as possible.

In this case engineers employ the use of a wedge so that tasks such as chopping firewood, cutting paper, and mowing our yards are made much easier. The wedge, as illustrated in Figure 4, is a simple machine often considered to be a slight variation of the inclined plane since it really consists of two inclined planes set back to back.

As a result, one end is thicker than the other so that a sharp cutting edge is formed. Figure 4. The wedge. While it is true that the wedge is very similar to the inclined plane physically, engineers use this machine for slightly different purposes. The inclined plane functions to transport heavy objects over a stationary surface, while the wedge itself can move in order to move or lift objects. Therefore, the wedge is essentially an inclined plane in motion.

When a wedge is moved, a forward force is converted into the outward or parting force used to separate or split material. Even though the wedge can also be used to lift or move objects a short distance, throughout history it has been primarily utilized as a valuable cutting device. An axe is a classic example of how a wedge is used to make work easier.

Can you imagine how hard it would be to cut down a tree or chop wood without an axe? Even the strongest of men pulling on a piece of timber in opposite directions could not complete the chore. Yet, generally one hefty swing of an axe will accomplish the feat with little effort.

In addition to the axe, other familiar tools such as a knife, shovel, plow and scissors all take advantage of the wedge in order to easily separate bound material. Can you think of other devices where the wedge is at work? Sometimes it is difficult to identify the wedge in the various engineering designs today because of the many different appearances it can have.

It is interesting, however, when we realize where the wedge can be found in as many unfamiliar places as well, such as the hull of a ship, airplane wings, and even our front teeth! While all six simple machines have their own distinct qualities, only the screw is able to convert a rotational force into a favorable linear force. This characteristic is desirable in many engineering applications where rotational motion is the only source of effort available to perform work, like a jet engine.

Similar to the wedge, the screw see Figure 5 is also closely related to the inclined plane since it is actually composed of an inclined plane wrapped around a cylinder. The spiraled edges around the cylindrical surface, commonly referred to as the screw threads, give the screw its ability to do work. Figure 5. The screw. Since engineers can apply this machine to two different unrelated applications, the screw has two general classifications: the fastening screw and the lifting screw.

In contrast to the wedge, which is designed with the ability to cut and separate material, the fastening screw is used to fasten and join two pieces of material together. This type of screw usually has sharp threads which cut into the parts being joined together.

The materials eventually become squeezed and held together between the head of the screw and its threads. Friction from the rough threads, on the other hand, keeps the screw from working loose over time. The lifting screw is the other type of screw, designed primarily for lifting or moving mass in a direction parallel to the axis of the screw.

Since the lifting screw must rotate many times in order to advance the load a short distance, work is made easier with its help. Although it may be hard to visualize, a great example of the lifting screw is a common propeller found on a small aircraft or boat. When the propeller is spun by a rotational force provided by the engine, a linear force is created along its rotational axis to produce thrust.

Aeronautical engineers have also found this tool to be exceptionally beneficial for helicopter rotors and jet engines as well. In addition to the propeller, a spiral staircase, nut and bolt, woodscrew, auger, drill bit, worm gear, and windmill are also good examples of how the screw is applied in many helpful engineering systems today.

It is well known that simple machines can make work easier, but exactly how much easier? The answer to this question is known as mechanical advantage, which is defined to characterize a machine's ability to lessen the burden of work. Mechanical advantage is the number of times a force exerted on a machine is multiplied by the machine, in other words, the degree to which a machine makes work easier. Recall from Lesson 1 that the mechanical advantage of all machines is defined by the general expression:.

However, this expression is too general and so it is necessary to define specifically the mechanical advantage of each machine in terms of their own unique mechanics. Furthermore, only the ideal, or theoretical, mechanical advantage of each simple machine is presented in this lesson since the actual mechanical advantage cannot be determined in advance.

Some of the associated activities in this unit such as Tools and Equipment, Part I , focus on both the ideal and actual mechanical advantage of a simple machine and how these values compare with one another. The inclined plane gains mechanical advantage by transferring some particular load over a long gradual incline rather than transporting it over a much shorter vertical path. Therefore, speaking in terms of mechanical advantage, since the path taken to raise the load is along the incline, the input distance is equal to the slope length and the output distance is the overall height of the inclined plane.

In other words, by advancing the load along the length of the slope, it is ultimately raised a vertical distance equal to the height of the plane. Accordingly, the ideal mechanical advantage of the inclined plane is written as:.

From this result we can easily see, as illustrated in Figure 6, that the longer the inclined plane is, the greater the mechanical advantage and the easier it is to accomplish work. Figure 6.

The mechanical advantage of the inclined plane. Figure 7. The mechanical advantage of the wedge. Dividing a piece of material is often a very troublesome exercise, yet a wedge can make this task become seemingly effortless.

With this simple machine, mechanical advantage is gained when an input force is applied to its end and converted into a greater outward or parting force acting on the bound material. Theoretically then, if a wedge is driven into a piece of material by its full length, then the object will be forced apart by a span equal to the thickness of the wedge's end.

Therefore, the input distance of a wedge is equal to its length and the output distance is equivalent to its end thickness as shown in Figure 7. Using this information, engineers can design a wedge with a variable mechanical advantage by simply adjusting its physical dimensions.

From a geometrical standpoint, the longer and thinner the wedge, the greater the mechanical advantage it provides. Since the screw must rotate many times to advance a load a short distance, the effort required to turn the screw is reduced and so mechanical advantage is gained.

Think of an inclined plane as a flat surface tilted upward, so that from the side it looks like a triangle; put two of those triangles together, base to base, and you've got a wedge. All machines, wedges and planes included, offer something called "mechanical advantage. Apply your force to the fat end of the wedge, and the thinner, opposite end -- the blade of a knife, say, or the sharp face of the chisel -- multiplies that force. Just as the wedge splits an object, the plane "splits" the force of gravity, some of it perpendicular to the plane's surface, some parallel to it, making it easier to push an object uphill than lift it outright.

The wedge is a moving inclined plane if you think of the plane as standing on its narrow end. A force applied at the opposite, wider, end has to go somewhere -- including the narrow end, which applies the force to a smaller area. Same force, smaller area, delivers a punch to whatever happens to be against the narrow end of the wedge: marble that Michelangelo is carving with a chisel, a log that Abe Lincoln's splitting with an ax, or that snowbank you're digging into with a shovel.

Meanwhile, from the perspective of the marble, log or snow, they're being shoved upward along the inclined plane of the face of the chisel, ax or shovel. Much easier than Michelangelo lifting "David," Lincoln hefting the log or you picking up a snowbank and waiting for the parts you don't want to drop off on their own. Just as the force you apply to a wedge acts along a distance -- from wide end to thin one -- the force you use to move objects along an inclined plane acts along a distance, too.

In the case of the inclined plane, you start at the thin end of the wedge, so to speak, and move up the plane to the wide end. A force applied to the outer rim of a wheel creates greater torque on the axle than the same force applied to an axle without a wheel.

A jar lid is a large screw. These ridges hold the jar and the lid together. A wheel and axle is a simple machine made of a rod attached to the center of a wheel. A wheel and axle is a special kind of lever that moves or turns objects. Instead of rolling a wheel forward to cut across the width of the pizza, you simply rock the blade to one side while continuing to apply downwards pressure. For example, a simple ordinary broom is a machine.

It is a form of a lever. They are a lever, pulleys, inclined plane, wheel and axle, screw, and wedge. The lever is used very often an example of a lever is a broom. With third class levers the effort is between the load and the fulcrum, for example in barbecue tongs.

Other examples of third class levers are a broom, a fishing rod and a woomera.