How to calculate the force of lever spanner

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.

When calculating the force, it has nothing to do with whether the lever is bent or not

because the arm of force is the distance from the fulcrum to the action line of the force, which has nothing to do with the shape of the lever. Finding out the arm of force can be calculated according to the lever balance condition. As shown in the figure below, the arm of force is the length of the dotted line, which has nothing to do with the shape of the rod

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