What are some of the simple machines we have been studying? Wedge, wheel and axle, lever, inclined plane, screw and pulley. Today we are going to look at two of the six simple machines— the inclined plane and the screw.
Resources In physics, a simple machine is any device that requires the application of only one force in order to perform work. Work is the product of the force applied and the distance moved due to the force. Most authorities list six kinds of simple machines: One can argue, however, that these six machines are not entirely different from each other.
Pulleys and wheels and axles, for example, are really special kinds of levers, and wedges and screws are special kinds of inclined planes.
Levers A lever is a simple machine that consists of a rigid bar supported at one point, known as the fulcrum. A force called the effort force is applied at one point on the lever in order to move an object, known as the resistance force, located at some other point on the lever.
A common example of the lever is the crow bar used to move a heavy object such as a rock. To use the crow bar, one end is placed under the bar, which is supported at some point the fulcrum close to the rock. A person then applies a force at the opposite end of the crow bar to lift the rock.
A lever of the type described here is a first-class lever because the fulcrum is placed between the applied force the effort force and the object to be moved the resistance force.
The effectiveness of the lever as a machine depends on two factors: The farther a person stands from the fulcrum, the more his or her force on the lever is magnified. Suppose that the rock to be lifted is only one foot from the fulcrum and the person trying to lift the rock stands 2 yd 1.
If he or she pushes down with a force of 30 lb Two other types of levers exist. In one, called a second-class lever, the resistance force lies between the effort force and the fulcrum.
A nutcracker is an example of a second-class lever. The fulcrum in the nutcracker is at one end, where the two metal rods of the device are hinged together. The effort force is applied at the opposite ends of the rods, and the resistance force, the nut to be cracked open, lies in the middle.
In a third-class lever, the effort force lies between the resistance force and the fulcrum. Some kinds of garden tools are examples of third-class levers.
When a person uses a shovel, for example, one holds the handle end steady to act as the fulcrum, while using the other hand to pull up on a load of dirt.
The second hand is the effort force, and the dirt being picked up is the resistance force. The effort applied by the second hand lies between the resistance force the dirt and the fulcrum the first hand.
Mechanical advantage The term mechanical advantage is used to described how effectively a simple machine works. Mechanical advantage is defined as the resistance force moved divided by the effort force used.
In the lever example above, for example, a person pushing with a force of 30 lb So, the mechanical advantage of the lever in that example was lb divided by 30 lb, or 6. The mechanical advantage described here is really the theoretical mechanical advantage of a machine.
In actual practice, the mechanical advantage is always less than what a person might calculate. The main reason for this difference is resistance. When a person does work with a machine, there is always some resistance to that work.
For example, a mathematician can calculate the theoretical mechanical advantage of a screw a kind of simple machine that is being forced into a piece of wood by a screwdriver. The actual mechanical advantage is much less than what is calculated because friction must be overcome in driving the screw into the wood.
Sometimes the mechanical advantage of a machine is less than one. That is, a person has to put in more force than the machine can move.
Class three levers are examples of such machines. A person exerts more force on a class three lever than the lever can move. The purpose of a class three lever, therefore, is not to magnify the amount of force that can be moved, but to magnify the distance the force is being moved.
As an example of this kind of lever, imagine a person who is fishing with a long fishing rod. The person will exert a much larger force to take a fish out of the water than the fish itself weighs.
The advantage of the fishing pole, however, is that it moves the fish a large distance, from the water to the boat or the shore. Pulleys A pulley is a simple machine consisting of a grooved wheel through which a rope runs.
The pulley can be thought of as a kind of lever if one thinks of the grooved wheel as the fulcrum of the lever.When I go online, I feel like one of B F Skinner’s white Carneaux pigeons. Those pigeons spent the pivotal hours of their lives in boxes, obsessively pecking small pieces of Plexiglas.
LESSON FIVE A Slide BIG IDEAS An inclined plane is a machine that changes the direction that force is applied and that helps decrease the effect of gravity, though it may increase friction. Different types of inclined planes form right triangles.
2 Unit 3 Simple Machines. Simple Machines. Unit 3 Simple Machines. Award-winning news and culture, features breaking news, in-depth reporting and criticism on politics, business, entertainment and technology. Even if the bank could not find a bona fide buyer, it was supposed to write down the property to fair market value on the books and take the loss on its financial statements.
Antique Copying Machines Left: Victoria copying machine, Le Bureau Moderne, Right: Minolta's update on copying machine advertising imagery.
Second image courtesy of the Museum of Business History and Technology. Offices need more than one copy of a document in a number of situations. National Geographic stories take you on a journey that’s always enlightening, often surprising, and unfailingly fascinating.