The origin of simple machines is indefinite. Ancient people might have used the idea of a pulley when they lifted heavy objects by throwing crude ropes or vines over tree branches, or the first levers were probably logs used to move heavy objects. Notwithstanding their antiquities, simple machines are significant sources of ease and comfort for all people living until today’s generation.
Millions of people ride a bike or motorcycle everyday and almost everyone uses a switch to turn on the lights or need a simple handle to open a door. Generally, people use levers, pulleys, inclined planes, or wedges in everyday life. These are simple machines that have been in use for thousands of years and that even the most complicated and most advanced mechanical technologies like power tools and automobiles are made up of. Even the simplest of the machines make manual chores or tough jobs easier. Machines enable a person to apply lesser force and at the same time increase the speed of work. They also reduce the amount of force required to move an object.
Lever
How the human arm works and how its muscles use force needed to move an object or lift weight is an example of a machine. It operates as a lever. A lever is one of the most used simple machines. In a normal situation, it would be impossible for a person to lift a ton of
weight. This is when levers are most helpful.
A lever is specifically used to lift heavy weights with the smallest amount of effort and is designed with three main components: the fulcrum, the load, and the effort. To do its work, a lever, which is a long, stiff bar or rod, must rotate or turn on a pivot point called fulcrum. The load is the item or object being lifted while the force applied by the person is the effort. How these components are arranged determines the class of the lever. There are three ways they can be arranged but the component that is in the middle mainly define what class the lever is.
The Class 1 lever is the most common and perhaps the most known. One example of this kind is the seesaw. In this class, the fulcrum always lies in the middle, and the force and load are placed at opposite ends. The force always moves in reverse direction of the load, and the lever obtains its mechanical advantage as the fulcrum is positioned nearer to the load.
Mechanical advantage (MA) is the distance from the fulcrum to the point where the force is applied divided by the distance from the fulcrum to the load. The lever’s mechanical advantage tells how much the machine increases effort. The MA may be greater than or less than 1 depending on the location of the fulcrum and the class of lever. The greater the MA, the lesser the effort needed to move a load.
In a Class 2 lever, the load is in the middle, the fulcrum is located at one end, and the effort is applied at the other end. Opposite to the first-class lever, the force and load of the second-class lever move in the same direction. However, both classes share the same principle when gaining mechanical advantage – that is when fulcrum and load get closer together. Wheelbarrows, nutcrackers, and wrenches are common examples of this type.
The Class 3 lever positions the load and fulcrum at reverse ends and force is applied in
the middle. The force and load also move at similar direction as the second-class lever but mechanical advantage cannot positively occur in third-class levers as force can never travel farther than the load. Some class 3 levers include tweezers, fishing poles, backhoes, cranes, and the human forearm where elbow is the fulcrum, and the forearm muscles apply the effort between the elbow and hand.
Commonly, the lever is longer than it is thick or wide, though not always, as in the case of the handle of a light switch. Levers also have limitations, one of which is that they can only operate through relatively small angles.
Pulley
Another simple machine that makes moving, pulling, and lifting easier are pulleys. Do you ever wonder how an elevator is lifted from the ground floor to the 50th floor or how a flag is raised to the top of a flagpole? This is because of a special type of wheel called a sheave or pulley. Pulleys are used for lifting by affixing the object to one end of the rope, threading the rope through the pulley or system of pulleys, and pulling on the opposite end of the rope.
Like levers, a pulley also has parts that work together to help people lift things. A pulley consists of a wheel that helps to support the load, a rope or a chain that helps to move the load, a groove that helps to hold the rope in place, and a load that is the object that will be lifted, pulled, or moved. However, in order to lift the load, someone or something needs to supply effort on the other edge of the rope.
Pulleys give a mechanical advantage that largely depends on the number of ropes that form the pulley. A single pulley gives a mechanical advantage of 1 while multiple pulleys, called block and tackle, can have mechanical advantages greater than 1. The mechanical advantage of a
block and tackle is equal to the number of strands of rope on the part of the block and tackle that is attached to the load.
Fixed Pulleys
A pulley on top of a flagpole is one common example of a fixed pulley. Fixed pulley changes the direction of the lifting force. This type of pulley is formed when the channeled wheel is attached to a surface. When using a fixed pulley to lift an object from the ground, the effort is applied downward rather than pulling the object upward. A fixed pulley is also a unique type among other pulleys. When it is attached to a rigid object, it acts as a Class 1 lever with the fulcrum being located at the axis and the rope being the bar. In using fixed pulleys, one does not have to push or pull the pulley up and down; however, one has to apply more effort than the load – an attribute distinct only to this kind of pulley. A fixed pulley does not provide concrete mechanical advantage. Although force may be applied in a different direction, similar quantity of force is needed to lift the load.
Movable Pulleys
Movable pulley is consist of a chain attached to some surfaces. When it comes to features and uses, movable pulleys are the exact opposite of fixed pulleys. A movable pulley lets a person use less effort to move the object from the ground, but one needs to push or pull the pulley up or down. This type is a pulley that moves with the load and is likened to a Class 2 lever where the load is between the fulcrum and the effort.
So long as the pulley is movable, it can offer mechanical advantages of greater than 1. When placed on the object to be moved, a single pulley can provide a mechanical advantage of 2 which means that twice the load can be lifted with only the same amount of effort. The MA of a
system of pulleys with a movable part equals the number of threads of rope coming from the movable part or the load being lifted.
Compound Pulleys
When fixed and movable pulleys are used together, a compound or combined pulley is formed. With this type of pulley, one can move a much greater load with much lesser effort. This multiple pulley system multiplies the strength and lifting power of the lifting machine, decreasing the effort on the winch and load. In most cases, the amount of effort needed to lift or pull an object is only less than half of the load; however, the travel distance it requires is very long. This type of pulley can be found on construction cranes.
Since long ago, systems of pulleys have been used to move heavy loads. Block and tackle and the chain hoist are two common forms of pulley systems. Block and tackle is frequently used with a motor while chain hoist is used manually. A block and tackle can house several movable and fixed pulleys; therefore, it can significantly increase the mechanical advantage. In a chain hoist, a closed loop of chain that is pulled by the hand joins a pulley system together. A chain hoist has two sections – the large and small pulleys, which diameters affect the mechanical advantage it provides.
The mechanical advantage in pulleys is greater as the distance over which the effort is applied increases. Distance is increased when more ropes to be pulled in lifting loads are added. Pulleys also consider the two types of MA: theoretical and actual. Theoretical MA is the mechanical advantage a machine would have if it were perfect while the actual MA takes into consideration the flaws in simple machines. The primary source of defect is friction which is the outcome of two objects rubbing each other. Friction is always present in almost every machine
in varying degrees. It always opposes motion; thus, giving pulleys a key problem because of the movement of the rope on the pulley and the load on the rope. To lessen this problem, pulleys are often applied with lubricants.
Inclined Plane
Slides, stairs, roller coasters, ladders, skateboard and wheelchair ramps have one thing in common – they are all inclined planes. This simplest of the simple machines might have adopted the principle of one person heading gradually to the top of the mountain. Histories record that even early Egyptians who lived around 2700 BC to 1000 BC had used earthen ramps to heave millions of large blocks of stone especially during the construction of the great pyramids; and they used lubricants to minimize the sliding friction in order to use the ramps more efficiently.
An inclined plane is a slanted surface used to move heavy loads up or down. Lifting heavy objects requires a lot of force but one will need lesser force to push it up an inclined plane. However, a longer distance is needed. The main principle of this simple machine is that the longer an inclined plane is, the easier it is to move an object along it and with less force.
Unlike levers or pulleys, inclined planes are not designed for lifting but for pushing heavy objects up or down. But similar to the other two simple machines, inclined planes give a mechanical advantage. The MA of a ramp measures how much the plane increases the effort applied to the machine. In taking the MA an inclined plane could give, one has to consider the theoretical and actual kinds. Because there is resistance (friction) that occurs when two objects are moving against each other, the actual mechanical advantage of a machine is less than its theoretical MA.
lift an object.
Suppose one has to lift a 70-pound barrel to a container van that is 4 feet off the ground. One needs to use 70 pounds of force for a 4-foot to move the barrel. But if he will use an 8-foot ramp to push the barrel up, he would only need half as much force to get the barrel in the van. If without friction, the mechanical advantage of an inclined plane is equal to the length of the plane divided by the altitude of the plane. A ramp that is twice longer than its height has an MA of 2 because the ramp increases twofold the effort the user applied or the user is only required to use half of the effort to move the load to a desired height. To further decrease the effort needed to lift an object, the user has to increase the ratio of the length of the ramp to the height of the ramp. This supports the idea why it takes more effort and is more difficult to climb up a steep hill than to walk up a longer, steadier path of the same height. A longer inclined plane gives a larger mechanical advantage. An inclined plane having the same length and height would give a mechanical advantage of 1 as it would simply run straight up and will not magnify the effort of the user.
Wedges
A form of inclined plane, wedges can multiply your effort in the same way as a slope can. Wedges help split objects such as stone or wood as it is made up of two inclined planes joined together at their bases to form a wide end and a narrow end. The force on the wide end of the wedge helps the narrow end cut through an object, and then the narrow end makes a path for the thicker one that makes the cutting or splitting possible. A wedge usually has one or two slanting sides.
While it is an adaptation of a ramp, it works differently from an inclined plane. In a wedge, the effort is applied directly to it while in an inclined plane, the effort travels along the plane. A wedge changes the direction of effort to help cut through a material. There is also much friction involve in using wedges which is why it is difficult to determine its mechanical advantage. A knife is one example of a wedge. In ancient times, people break wood using wedges. They transfer the force they applied to the cutting edge out to the sides of the wedge. Wooden wedges were also used during the prehistoric times to cut through rocks.
Dry wooden wedges were inserted into rocks’ crevices and allowing them to swell by absorbing water. The rocks split because of the resulting pressure in the cracks. Generally, wedges are useful for cutting, splitting, and pushing objects.
The power of simple machines cannot be underestimated. For very long years, simple machines have made every work easier and faster for people. They are so significant that even the simplest task like opening a door cannot be done without them. From the plainest to the most complex, state-of-the-art equipment that flood one’s home, these simple machines are valuable part of it. While we appreciate the functions of high technologies today, it is but essential to not forget the basic.
Works Cited
Griffin, Jr., Odis Hayden. “Machine.” Microsoft Encarta 2009. Washington: Microsoft
Corporation, 2008. DVD. 23 Apr. 2012.
St. Andre, Ralph. Simple Machines Made Simple. United States of America: Greenwood
Publishing Group, 1993. Print.
