information from wikipedia
TRANSCRIPT
Then, we learned from website that lever has three classes. These classes represent variation in the relative locations of the fulcrum, the load and the force.
Information from Wikipedia http://en.wikipedia.org/wiki/Lever
The fulcrum is located between the applied force and the load. In this class, seesaw, crowbar and scissors are all great examples.
Information from Wikipedia http://en.wikipedia.org/wiki/Lever
The load is situated between the fulcrum and the force. Wheelbarrow and nutcracker can clearly explain this class’s characteristic.
Information from Wikipedia http://en.wikipedia.org/wiki/Lever
The force is applied between the fulcrum and the load. Tweezers and mandible are under this class.
Information from Wikipedia http://en.wikipedia.org/wiki/Lever
However those three classes seemed not that pragmatic in our daily life. So, after further study, we found another classification of lever, this method is obviously easier to understand…
According to the different effects lever has, the lever can also be divided into another three types.
Respectively, they are: saving-power
lever; laborious-power lever; equal-power lever
• Definition: the lever which has the power greater than the resistance arm of the lever arm
• Advantage: save force and power
• Disadvantage: need relative long distance
• Definition: the lever which has the force equal to the resistance arm of the lever arm
• Advantage: ------
• Disadvantage:------
Notice: Since this kind of lever is neither save the power nor save the distance, we are not sure what are its strong points and drawbacks.
• Definition: the lever which has power less than the resistance arm of the lever arm
• Advantage: short distance
• Disadvantage: laborious
Leverage is also been called as “the equilibrium conditions of lever”. To make lever attain equilibrium state, the number of forces acted upon on the two points of the lever must have inverse relationship with their force arms
• Mechanical force × Power arm = Resistant force × Resistance arm
• Using algebra to express it as F1 • L1 = F2 • L2
• In this expression, F1 stands for mechanical force L1 stands for power arm, F2 represents resistant force L2 represents resistance arm
The portrait of Archimedes
(1) without the weight of the rod ends of equal distance from the pivot mount equal weight, they will balance
(2) without the weight of the rod ends at equal distances from the pivot mount not equal the weight of the heavy end of the declination
(3) without the weight of the rod ends are not equal distance from the fulcrum of an equal weight hanging from the far end of the declination
(4) the role of a weight can be uniformly distributed with a few to replace the role of weight, as long as the center of gravity remains unchanged. Instead of several uniform distribution of weight can be a hanging in their center of gravity at the place of weight
Lever of Archimedes not only stayed on the theoretical aspects, but also carried out a principle whereby series of inventions.
It is said that he had the help of levers and pulleys, so parked in the beach into the water on masts as well, in the defense of Syracuse against the Roman naval attack in the battle, the principle of Archimedes created a much leverage, close of the sling, use it to shoot a variety of missiles and stones to attack the enemy, once outside the city the Romans arrested at Syracuse for 3 years.
M1×r2×L1= M2 ×r1×L2
In which: M1 is moment torque, M2 is resistance torque, L1 is power arm, L2 is resistance torque, r1 is radius of moment torque, r2 is radius of the inner resistance torque
For example: we can use the 2rd principle of leverage to solve the hard nut called the real long-term CVT when dealing with the mechanical transmission.
The second principle of leverage is created to do the problems that the first principal cannot solve.
as a matter of fact, laborious-power levers occupy human body’s levers in a great measure, and the others are equal-power and saving-power lever.
When you nod your head, the pivot is the place where the skull meets the top of the spine. The lever arm is your skull. You use your the neck muscles to surmount the load caused by the weight of the head and lift your head up.
When you stand on your tip toes, the tip toe is the pivot and the muscle on your heel exerts a pulling force upward, equaling the effect of your weight’s gravity of your weight. Since the pulling force of muscle is less than the weight, this set is a laborious-power lever. Besides, the longer your feet are, the less force you need to spend.
During the process of lifting up heavy goods, arm acts as the lever and elbow point is the pivot. This set is a laborious-power lever. Usually, people need to spend six more strength to lift up the goods; however, it can save the distance.
Wikipedia http://en.wikipedia.org/wiki/Lever
Baidu Baikehttp://baike.baidu.com/view/85069.htm
Google image http://www.google.com/images?q=%E6%9D%A0%E6%9D
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