How does leverage count

1. 1、 Lever
(1) basic concept of lever
a hard rod that can rotate around a fixed point under the action of force is called lever
there are five terms of lever: ① fulcrum: the point around which the lever rotates (o); ② Power: the force that makes the lever rotate (F1); ③ Resistance: the force that prevents the rotation of the lever (F2); ④ Power arm: distance from fulcrum to action line of power (L1); ⑤ Resistance arm: distance from fulcrum to resistance action line (L2)< (2) the condition of leverage balance × Power arm = resistance × The resistance arm, the equilibrium condition, is the lever principle discovered by Archimedes< (3) three levers:
1. Labor saving lever: L1 & gt; L2, F1 & lt; F2 The feature is labor saving, but it costs a lot of distance (e.g. iron scissors, guillotine, driver)
② lever: L1 & lt; L2, F1 & gt; F2 The characteristic is laborious, but saves the distance (e.g. fishing rod, barber scissors, etc.)
③ equal arm lever: L1 = L2, F1 = F2 when balancing. It is characterized by no effort and no effort Such as: balance)
2. Buoyancy
(1) buoyancy
the upward force of liquid or gas on an object immersed in liquid or gas is called buoyancy. The cause of buoyancy is: the object immersed in liquid (or gas) is subject to the upward and downward pressure difference of liquid (or gas). Buoyancy is applied to liquid (or gas), buoyancy belongs to elastic force
(2) Archimedes principle
an object immersed in liquid is subject to upward buoyancy, which is equal to the gravity of the liquid it displaces. Expression: F = g row= ρ Liquid V discharges g (Archimedes principle also applies to gas)
it can be concluded that the density of the liquid and the volume of the liquid displaced by the object are two factors that affect the buoyancy< (3) the calculation method of buoyancy
① Archimedes principle: F floating = g row= ρ Liquid V row g (also suitable for gas)
② two force balance: F floating = g object (suitable for floating and suspension)
③ multi force balance: F floating = G-F (this is the case of measuring buoyancy with a spring dynamometer)
④ pressure difference method: F floating = f up-f down (not commonly used)
(4) measurement of buoyancy
① common method: measure the gravity g of an object with a spring dynamometer, When an object is immersed in the liquid and the indication F of the spring dynamometer is read out, the buoyancy of the object immersed in the liquid is: F floating = G-F< (2) measuring v-row (measuring cylinder) method: measure v-row and use f = g-row= ρ The buoyancy of liquid V row G is calculated
(5) the buoyancy and sinking conditions of objects are determined by the relationship between gravity and buoyancy. ① When gravity is greater than buoyancy, the object sinks; ② When gravity equals buoyancy, the object floats; ③ When gravity is less than buoyancy, the object floats< (6) utilization of buoyancy
1. Ship: hollow method is used to increase the available buoyancy, so that the ship can float on the water. The size of a ship is expressed in terms of its displacement - the mass of boiled water discharged when it is fully loaded
② submarine: submarine floats and sinks by changing its own gravity
③ balloons and airships: both use the buoyancy of the air to work. Balloon and airship lift, mainly by changing the volume of the airbag to change their own buoyancy to achieve.

2. The fulcrum is the center of mass of the lever, the force lever must be balanced, otherwise it is a variable force, the lever balance conditions: 1. All forces move to the center of mass, the resultant force is 0. 2. The sum of moments is 0

3. As shown in the figure, we know the size relationship between the power arm and the resistance arm, and the size of the resistance g. we can calculate the size of F by using the balance condition of the lever × L 1 =G × So the answer is: 20n

4. Each specification of the proct has a margin ratio, divided by 1 margin ratio is leverage ratio. For example, what I do is Xinhua oil. The margin ratio is 3% or 5%, and the leverage is 1 / 3% = 33.3 times and 1 / 5% = 20 times. It's illegal for the state to stipulate that it's more than 50 times. For example, the leverage of spot gold is 1:100. For example, if you buy a hand of gold now, you actually buy and sell 100 ounces of gold. Leverage actually means that every proct has a margin ratio. Dividing 1 by the margin ratio is the leverage ratio. For example, what I do is Xinhua oil. The margin ratio is 3% or 5%, and the leverage is 1 / 3% = 33.3 times and 1 / 5% = 20 times. It's illegal for the state to prescribe that it's more than 50 times. Pay attention to this.
for example, the leverage of spot gold is 1:100. For example, if you buy one hand of gold now, you actually buy and sell 100 ounces of gold. In fact, leverage means small and broad

5. To make the lever balanced, the magnitude of the two forces (power and resistance) acting on the lever is inversely proportional to their arm of force. power × Power arm = resistance × The resistance arm is expressed as F & # 8226; L1=W• L2 Where f is power, L1 is power arm, W is resistance and L2 is resistance arm

if the lever is unbalanced, it will rotate at a variable speed, and then make an equal penlum motion under ideal conditions. The specific calculation can be solved by the law of conservation of mechanical energy, that is, EP = EK (MGH = 1 / 2 * MV ^ 2)

6.

Suppose power F1, resistance F2, power arm length L1, resistance arm length L2, then the formula of lever principle is: f1l1 = f2l2

there are the following four kinds of transformation:

F1 = f2l2 / L1

F2 = f1l1 / L2

L1 = f2l2 / F1

L2 = f1l1 / F2

five elements of lever:

1, support point: the point around which the lever rotates, which is usually represented by the letter o

Power: the force that makes the lever rotate, usually expressed as F1

3. Resistance: the force that hinders the rotation of the lever, usually expressed as F2

Power arm: the distance from the fulcrum to the dynamic action line, usually expressed by L1

Resistance arm: the distance from the fulcrum to the resistance action line, usually expressed as L2

(Note: the dynamic action line, resistance action line, power arm and resistance arm are all represented by dotted lines. The lower corner mark of the force arm changes with the lower corner mark of the force. Example: if the power is F3, the power arm is L3; The resistance is F5 and the resistance arm is L5.)

extended data:

balance condition of leverage:

power × Power arm = resistance × Resistance arm

formula:

F1 × L1=F2 × L2 variant:

F1: F2 = L2: L1 the power arm is several times of the resistance arm, so the power is a fraction of the resistance

formula:

F1 × L1=F2 × L2 if a hard stick can become a lever, it must not only have a powerful function, but also be able to rotate around a fixed point. Without any conditions, a hard stick cannot become a lever. For example, when a wine bottle driver is not in use, it cannot be called a lever

power and resistance are relative, whether it is power or resistance, the object under force is a lever, and the object acting on the lever is the object exerting force

7. power × Power arm = resistance × The resistance arm
applies force by hand until the lever power increases until the lever power increases × Power arm ≥ resistance × Resistance arm
the stone is pried up.

8.

Conclusion: when the fulcrum is between two forces, the two forces are vertical and the lever is balanced, the force on the fulcrum is always equal to the sum of the two forces

the following is an example:

clipping is shown in the figure. The diameter of pin C and copper wire is d = 5mm. When the applied force P = 200N, calculate the average shear stress of the cross section between the copper wire and the pin τ It is known that a = 30mm, B = 150mm

9. The same as LS
power * power arm = resistance * resistance arm

[sure enough, LZ, if you have a book, just read the book handle = =]

10. The most reliable and easy to understand research tool is the pole used by the folk. A moving position of the weight can balance the weight in front of it.