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San Soo Sifu
Joined: 03 Jun 2007
Posts: 1113
Location: Salem, Oregon, USA
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 Posted: Thu Mar 04, 2010 5:55 pm Post subject: Classification of Levers |
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| San Soo Sifu wrote: | From: San Soo Sifu (SanSooSifu) 12/23/2001 10:04 am
To: BobShores (3 of 9)
188.3 in reply to 188.2
| Odis Hayden Griffin, Jr. wrote: | LEVER
I. Introduction
Lever, simple machine consisting of a rigid bar that rotates about a fixed point, called a fulcrum. Levers affect the effort, or force, needed to do a certain amount of work, and are used to lift heavy objects. To move an object with a lever, force is applied to one end of the lever, and the object to be moved (referred to as the resistance or load) is usually located at the other end of the lever, with the fulcrum somewhere between the two. By varying the distances between the force and the fulcrum and between the load and the fulcrum, the amount of effort needed to move the load can be decreased, making the job easier.
Physicists classify the lever as one of the four simple machines used to do work. (The other three are the pulley, the wheel and axle, and the inclined plane.) Work is defined in physics as the result of a force, such as a person lifting, that moves an object over a distance. A common example of a lever is the seesaw. The human arm is also a lever, where the elbow is the fulcrum and the muscles apply the force.
II. Work and Mechanical Advantage
A lever makes work easier by reducing the force needed to move a load. Work, in physics, is the product of the force used to lift a load multiplied by the distance the force, or effort, is applied. This relationship can be written mathematically as:
Work = Force × Distance
The amount of work needed to move an object a given distance always remains the same except when friction is present. The lever, like all simple machines, makes doing work easier by reducing the force needed to move an object. In order to reduce the force needed, the distance over which the force is applied must be increased.
To increase this distance, the load to be moved must be close to the fulcrum and the force must be applied far from the fulcrum. A good example is a claw hammer used to pry nails loose. The user's hand applies force to the handle at one end of the lever. The head of the hammer is the fulcrum, and the nail at the other end of the lever is the load to be moved. The nail is much closer to the fulcrum than is the hand applying the force. Since the hand is farther away from the fulcrum, the force travels a greater distance than does the load as the nail is pried loose. The same amount of work would have been done if the nail had been pulled directly out by hand. However, by using the lever the force was spread out over a greater distance, and so less force was needed. Another example is a seesaw. The force of a smaller person can balance and even lift the load of a larger person as the smaller person moves farther away from the fulcrum.
The mechanical advantage (MA) of a lever tells how much the lever magnifies effort. The greater the MA, the less the effort needed to move a load. The MA of a lever is the ratio of the distance the force travels to the distance the load travels. In practical terms, the MA is the distance of the force to the fulcrum divided by the distance of the load to the fulcrum. Depending on the class of lever and the location of the fulcrum, the MA may be less than or greater than 1.
III. Types of Levers
There are three different classes of levers, depending on the arrangement of the force, the load, and the fulcrum along the lever bar. Each class of lever affects force in a different way, and each class has different applications.
A. Class 1 Levers
The class 1 lever has the fulcrum between the force and the load, as in a seesaw. When two people of equal weight use the seesaw, they position themselves an equal distance from the fulcrum, and the system is balanced. When a heavier person sits on one end, that person usually moves toward the center, which gives a mechanical advantage to the lighter person so that the system is again in balance. It is possible for a class 1 lever to have a significant mechanical advantage.
B. Class 2 Levers
The class 2 lever has the fulcrum at one end, the force at the other end, and the load in the middle. A common example is the wheelbarrow, where the wheel is the fulcrum, the load rests within the box, and the force is the lift supplied by the user. A class 2 lever always has a mechanical advantage of greater than 1. To reduce the force required by the user even more, the best wheelbarrow design is one where the wheel is directly under the load, reducing the distance from the load to the fulcrum almost to zero. Many wheelbarrows and garden carts are designed in that manner to make them easy for the user to move.
C. Class 3 Levers
A class 3 lever has the fulcrum at one end, the load at the other end, and the force in the middle. The human forearm is a class 3 lever. The elbow is the fulcrum, and the muscles of the forearm apply the force between the elbow and the hand. The class 3 lever always has a mechanical advantage of less than 1, because the load travels a greater distance than the force travels. Consequently, the work requires more effort than would ordinarily be needed. Although they boost the amount of effort needed, class 3 levers are useful for increasing the speed at which a load is moved. A baseball bat and a broom are also examples of class 3 levers, with which a greater effort results in a smaller load moving at a greater speed.
IV. History
The first levers were probably branches or logs used to lift heavy objects, followed by sticks used to till soil for planting crops. In both of those applications, the lever magnifies the force applied by a human. Learning to use those simple tools led to the development of other applications of the lever.
In addition to using human power as the force applied to the lever, people added weights so that the force they had to exert was lessened. These weights are called counterweights. A counterbalanced lever called a shadoof was used in ancient Egypt for lifting irrigation water from the Nile River up onto land, and it is still used today. During the Middle Ages, attacking armies used a similar device for lifting soldiers over fortress walls. The principle of the lever was often utilized through the rotary motion of the wheel and axle. Waterwheels installed near waterfalls used the continuous force of moving water to provide the necessary leverage to turn large grindstones for grinding grain into flour.
A crowbar and the claw of a hammer used to pry loose nails are both common examples of levers in action. Balance scales use levers to find the mass of an object. Complex machines often use a series of levers to transfer force. The keys of a piano use levers to transmit force from the keys to the hammers that strike the strings.
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Contributed By:
Odis Hayden Griffin, Jr., B.S., M.S., Ph.D., Director and Professor, Division of Engineering Fundamentals, Virginia Polytechnic Institute and State University. |
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Hit First...Hit Hard...Hit Often...and Finish Him Off! |
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San Soo Sifu
Joined: 03 Jun 2007
Posts: 1113
Location: Salem, Oregon, USA
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| Posted: Thu Mar 04, 2010 6:01 pm Post subject: WHEEL and AXLE |
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| San Soo Sifu wrote: | From: San Soo Sifu (SanSooSifu) 12/22/2001 10:37 pm
To: BobShores (2 of 9)
188.2 in reply to 188.1
| W. David Lewis wrote: | WHEEL and AXLE
Wheel and axle is a mechanical device used in lifting loads. It is one of the six simple machines developed in ancient times and ranks as one of the most important inventions in history. The simplest wheel and axle has a cylinder and a large wheel, fastened together and turning on the same axis.
The wheel and axle is a first-class lever. The center of the axle (the cylinder) corresponds to the fulcrum. The radius of the axle corresponds to the load arm. The radius of the wheel corresponds to the force, or effort, arm to which force is applied. Sometimes a crank is used instead of a wheel.
The advantage of a wheel and axle is that it can lift heavy loads with little effort on our part. The following law gives the ratio between the two: The force applied multiplied by the radius of the wheel equals the load multiplied by the radius of the axle. To reduce this to a formula, let F stand for force; R for the radius of the wheel; L for the load; and r for the radius of the axle. F X R = L X r, or L/F = R/r
The mechanical advantage of a machine is always the ratio of the load (L) to the force (F). Let us use an example in which the radius of the wheel (R) is 10 inches, the radius of the axle (r) is 1 inch, and the load (L) is 20 pounds. If there were no friction, the formula would be 20/F = 10/1. Since 10F = 20, the force needed would be the same as that normally used to lift a mere 2 pounds. The mechanical advantage, the ratio of L to F, would be 20/2, or 10.
Uses of the wheel and axle. In the ordinary windlass used for raising water from a well, a crank replaces the wheel. The hand applies the effort to the crank. The weight of the bucket of water is the load. In a grindstone, the radius of the wheel is usually longer than the crank handle, because speed is needed as well as force. Sometimes teeth or cogs may be placed around the edge of the wheel, as in a cogwheel, or on the sprocket wheel of a bicycle.
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Contributor:
• W. David Lewis, Ph.D., Distinguished University Professor, Auburn University. |
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_________________
Hit First...Hit Hard...Hit Often...and Finish Him Off! |
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San Soo Sifu
Joined: 03 Jun 2007
Posts: 1113
Location: Salem, Oregon, USA
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| Posted: Thu Mar 04, 2010 6:15 pm Post subject: An Unnamed Lever |
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| San Soo Sifu wrote: | From: San Soo Sifu (SanSooSifu) 12/22/2001 5:18 pm
To: ALL (1 of 9)
188.1
Here is a lever that went unmentioned over at East Hills. I will give the real-life example, then I will include a Kung-Fu San Soo lesson to better illustrate the lever principle.
The water-well hand crank (windlass). The water-bucket bringing up the weight of the water is the load. The spinning wood cylinder that the rope is tied to is the fulcrum. The hand crank is the lever. Your hand turning the crank is the force (effort).
Opponent throws a left straight punch, stepping with his left foot forward. Step to the outside with your right foot forward, block and hold with a left up windmill. Left semi-roundhouse kick to his spleen. Step down into a left cross step (your left foot toes are pointing the same direction as your opponent). Take your opponent's left wrist and bend up towards his left armpit / back of his left arm area, applying a wrist leverage. You will form an "L" shape with his left forearm & left upper arm bent at a 90 degree angle. His left elbow will be pointing at your face, his left wrist will be bent, and his left fingers will be pointing up at the ceiling. Sweep the front of his left shin with the back of your right calf; while pushing / striking the back of his left triceps area forward with your right hand, and pulling his left hand / left wrist backwards with your left hand. Flipping him forward onto his back. Open follow up.
Your opponent's bent left arm is the lever. His left shoulder ball and socket joint is the fulcrum. His body from head-to-toe, straight down his imaginary centerline, is the load. Your pulling left hand and pushing / striking right hand is the force (effort).
The lever is being cranked faster than the fulcrum can move the load. In the studio, we go nice & easy for the sake of our workout partner's health and well-being.
In the street, we do not care.
If we flip our opponent onto his back, that is fine. If we cause our opponent to do a face plant or head plant into the cement, that is fine too. If we cause our opponent to have his left shoulder ball and socket joint ripped out of joint, that is especially fine! |
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Hit First...Hit Hard...Hit Often...and Finish Him Off! |
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