How to calculate the force of three pulley combinations

1.

1. In theory, the most labor-saving assembly method of three pulleys can only use one sixth of the weight force

the combination method is as shown in the figure:

calculation method: under ideal conditions, the relationship between tensile force and gravity f = 1 / 2 * 1 / 2 * 1 / 2G = 1 / 6G

extended data:

1 Mechanical efficiency of pulley

wtotal = w you + W amount

wtotal = work done by power to machinery

wtotal = work done by machinery to object

wtotal = work done to overcome gravity and friction of machinery

wtotal = work done to overcome gravity and friction of machinery η= Wyou / wtotal (any machine will inevitably do extra work, the effective work is always less than the total work, so the mechanical efficiency is always less than 1. Mechanical efficiency is usually expressed as percentage)

2. Calculation of movable pulley:

1. F = g / 2 (idealized, without considering the weight of pulley and only one movable pulley)

2. F = (G + G movable pulley) / 2 (considering the weight of movable pulley and only one movable pulley)

3. F = (G + G movable pulley) / N (n represents the number of segments of rope connected to movable pulley, This is a pulley block)

3. Classification of pulley block:

pulley block is composed of a certain number of fixed pulleys and movable pulleys and ropes around them. The pulley block has the function of saving labor and changing the direction of force, which is an important part of lifting machinery

the number of ropes that the pulley block jointly bears the construction weight is called the number of working lines. Usually, the name of pulley block is expressed by the number of fixed pulley and movable pulley. For example, the pulley block composed of four fixed pulleys and four movable pulleys is called four pulley block

2.

There are two methods for the pulley block composed of three pulleys, as shown in the figure

regardless of friction and the dead weight of pulley and rope, the tension in the left figure is 1 / 3 of gravity, saving 2 / 3 of force

the tension in the right figure is 1 / 4 of gravity, saving 3 / 4 of force

I think the question is wrong, such as how much force is saved, it is "3 / 4", If you ask what is the most economical pulling force, it is "1 / 4"

3. Three pulleys, one fixed pulley, two movable pulleys, one end of the rope is fixed on the fixed pulley
four pulleys, two movable pulleys, two fixed pulleys, one end of the rope is fixed on the movable pulley
the first two people are too stupid, how can they pull the four movable pulleys

4.

One fixed pulley and two movable pulleys are the most labor-saving

Generally speaking, the number of segments n of the rope bearing the weight of the object is determined first, and then the rope is wound according to the principle of "odd and even, from the inside out"

2. Pay attention to some special requirements when determining the rope winding of pulley block, such as "the most labor-saving", "people should stand on the ground", "pull down" and so on, and conform to certain physical situations

3. When using the pulley block, the pulley block is suspended by n sections of rope, and the moving distance of the free end of the rope is n times of the moving distance of the object, which is expressed by the formula: S = NH

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extended data:

1. Mechanical efficiency of pulley

wtotal = w you + W amount

wtotal = work done by power to machinery

wtotal = work done by machinery to object

wtotal = work done by overcoming gravity and friction of machinery

1 η= Wyou / wtotal (any machine will inevitably do extra work, the effective work is always less than the total work, so the mechanical efficiency is always less than 1. Mechanical efficiency is usually expressed as a percentage)

2. Calculation of movable pulley:

1. F = g / 2 (idealized, without considering the weight of pulley and only one movable pulley)

2. F = (G + G movable pulley) / 2 (considering the weight of movable pulley and only one movable pulley)

3. F = (G + G movable pulley) / N (n represents the number of segments of the rope connected to the movable pulley, which is a pulley block)

5. One fixed pulley and two movable pulleys
starting from the fixed pulley, winding around the first movable pulley (i.e. ordinary pulley block with 1 / 2 force saving) saves 1 / 2 of the force, bypassing the groove of the fixed pulley upward and then passing down the second fixed pulley, saving 3 / 4 of the force at this time

6. One fixed pulley and two movable pulleys
start from the fixed pulley
wrap around the first movable pulley (i.e. the pulley block that saves 1 / 2 force) to save 1 / 2 force
go up around the groove of the fixed pulley and then go down through the second fixed pulley to save 3 / 4 force

8. Save up to five sixths of the effort

9. Junior high school physics formula

[share] junior high school physics formula

physical quantity calculation formula remarks
speed υ= S / T 1m / S = 3.6 km / h
sound velocity υ= 340m / s
speed of light C = 3 × 108 M / s
density ρ= M / v 1 g / C m3 = 103 kg / m3
resultant force F = F1 - F2
F = F1 + F2, F1 and F2 are on the same straight line with opposite direction
F1 and F2 are on the same straight line with the same direction
pressure P = f / s
p= ρ G H P = f / S is suitable for solid, liquid and gas
P= ρ G H is suitable for vertical solid column
P= ρ The pressure of liquid can be calculated directly by G H
1, standard atmospheric pressure = 76 CMHG, column = 1.01 × 105 PA = 10.3 m water column
buoyancy (1) f floating = g – f
2) floating and suspending: F floating = g
3) f floating = g row= ρ Liquid g V row
④ judge the buoyancy according to the floating and sinking conditions (1) judge whether the object is subject to buoyancy
(2) judge the state of the object according to the floating and sinking conditions
(3) find out the appropriate formula to calculate the buoyancy
object floating and sinking conditions (premise: the object is immersed in liquid and only subject to buoyancy and gravity):
① f floating > G ρ Liquid ＞ ρ Floating up to floating (2) f floating = g ρ Liquid= ρ (3) f < G ρ Liquid ＜ ρ Lever balance condition F1 L1 = F2 L2 lever balance condition is also called lever principle
pulley block f = g / N
F = (g dynamic + G material) / N
SF = n SG ideal pulley block
neglecting the friction between axles
n: number of strands of rope acting on the moving pulley
work w = f s = P T 1J = 1n & 8226; m = 1W• S
power P = w / T = f υ 1kW = 103w, 1MW = 103kW
useful work w useful = GH (vertical lifting) = f s (horizontal movement) = wtotal – w amount= η Wtotal
additional work wtotal = wtotal – wyou = gdynamic H (ignoring friction between axles) = FL (inclined plane)
total work wtotal = w useful + wtotal = f s = w useful/ η
mechanical efficiency η= W useful / W total
η= G / (n, f)
= g object / (g object + G motion) definition formula
is applicable to moving pulley Pulley block

all the formulas of physics for senior high school entrance examination

features or principles series circuit parallel circuit
time: t t t = T1 = T2 t = T1 = T2
current: I I I = I 1 = I 2 I = I 1 + I 2
voltage: u u = U 1 + U 2 u = U 1 = u 2
charge quantity: Q electricity Q electricity = q electricity 1 = q electricity 2 Q electricity = q electricity 1 + Q electricity 2
resistance: r r r r = R 1 = R 2 1 / R 1 + 1 / R 2 />Electric work: w w = w 1 + W 2 w = w 1 + W 2
Electric Power: P P P = p 1 + p 2 P = p 1 + p 2
electric heating: Q heat Q heat = q heat 1 + Q heat 2 Q heat = q heat 1 + Q heat 2
physical quantity (unit) formula remarks formula deformation
velocity V (M / s) v = s: distance / T: time
gravity g
(n) g = mg m: mass
G: 9.8N / kg or 10N / kg
density ρ < br />kg/m3 ρ=
m: mass
V: Volume
resultant force
(n) same direction: F = F1 + F2
opposite direction: F = F1-F2, opposite direction, F1 & gt; F 2
buoyancy f float
(n) f float = g object - G view g view: gravity of object in liquid
buoyancy f float
(n) f float = g object this formula is only applicable to
floating or levitation of object
buoyancy f float
(n) f float = g row = m row G= ρ Liquid GV discharge g discharge: gravity of discharged liquid
m discharge: mass of discharged liquid
ρ Liquid: density of liquid
v-row: volume of liquid
(i.e. volume immersed in liquid)
equilibrium condition of lever f1l1 = f2l2 F1: power L1: power arm
F2: resistance L2: resistance arm
fixed pulley f = g object
s = H F: tension on free end of rope
G object: gravity of object
s: distance of free end of rope moving
H: object lifting High distance
moving pulley f = (g object + G wheel)
s = 2 h g object: gravity of object
G wheel: gravity of moving pulley
pulley block f = (g object + G wheel)
I'm glad to answer for you. If you have any mistakes, please understand

10. Only one movable pulley can save half the force