Xiaohua did the experiment of "estimating the value of atmospheric pressure." (1) please complete the following experimental steps. A. push the piston of the syringe to the top of the syringe barrel______ Then seal the small hole of the syringe with a rubber cap. B. fasten the neck of the piston of the syringe with a fine nylon rope so that one end of the rope is connected with the hook of the spring dynamometer, and then pull the syringe barrel horizontally and slowly to the right______ Write it down______ It is equal to the pressure of the atmosphere on the piston, F.C______ , denoted as l, read out the volume V of the syringe, then the area s of the piston=______ Finally, the value p of atmospheric pressure at this time is calculated=______ (write the expression with the measured quantity). (2) in the experiment, Xiaohua used the measuring instrument correctly, and the reading was correct, but she found that there was always deviation in the measurement results, which may be caused by (write two points)______ ．

Xiaohua did the experiment of "estimating the value of atmospheric pressure." (1) please complete the following experimental steps. A. push the piston of the syringe to the top of the syringe barrel______ Then seal the small hole of the syringe with a rubber cap. B. fasten the neck of the piston of the syringe with a fine nylon rope so that one end of the rope is connected with the hook of the spring dynamometer, and then pull the syringe barrel horizontally and slowly to the right______ Write it down______ It is equal to the pressure of the atmosphere on the piston, F.C______ , denoted as l, read out the volume V of the syringe, then the area s of the piston=______ Finally, the value p of atmospheric pressure at this time is calculated=______ (write the expression with the measured quantity). (2) in the experiment, Xiaohua used the measuring instrument correctly, and the reading was correct, but she found that there was always deviation in the measurement results, which may be caused by (write two points)______ ．

(1) A. push the piston of the syringe to the bottom of the syringe barrel, exhaust the air in the barrel, and then seal the small hole of the syringe with a rubber cap. B. when the piston in the syringe begins to slide at a uniform speed, the tension of the spring dynamometer is just in balance with the atmospheric pressure, so it is necessary to record the indication at this time

On physical pressure in junior high school
The maximum water level difference between the upstream and downstream of the Three Gorges dam can reach 113m. The upstream ships have to pass through five lock chambers to make the hull gradually lower. The water level of each lock chamber changes more than 12M, so the gate of Shanxia ship lock is very large. Each miter gate has a height of 39.5m and a width of 20.2m, What is the pressure n ~ (G is 10N / kg,)

P = 1000kg / m3 * 10N / kg * 30m * 1 / 2 = 150000pa
S = 30 m * 20.2 M = 606 M2
F=PS=90900000N

Two identical cylindrical containers are filled with water and alcohol respectively (the density of water is relatively high). The solid metal ball a with the same volume is immersed in water and the solid metal ball B is immersed in alcohol, and there is no liquid overflow. At this time, the pressure of water and alcohol on the bottom of the container is equal
The quality of water in cup a is less than that of alcohol in cup B
There are two cubes A and B respectively placed on the horizontal table top, and the density of a is relatively high. Two cubes with the same height are cut off horizontally on the two cubes A and B respectively, and the pressure of the remaining parts on the horizontal table top is equal
Correct answer) p a > P B

1. Let the mass of water and alcohol be M1 and M2 respectively,
When a solid metal ball with the same volume is immersed in water and B in alcohol, it is equivalent to adding the same volume of water and alcohol into two containers respectively. Because their density is different, it is equivalent to adding different mass, m water > m alcohol. Because they are two identical cylindrical descriptors, and the pressure of water and alcohol on the bottom of the container is equal at this time, there are: M1 + M1 = M2 + m2, m water > m alcohol, So there are: M1 ρ 2, so ρ 1GH > ρ 2GH
It is not difficult to see that ρ 1gh1 > ρ 2gh2
That is p a > P B

Where n is the positive pressure. What is the positive pressure?
RT, what is positive pressure? How to judge this kind of problem,

Positive pressure is pressure
For example, if an object is placed horizontally on a table, the positive pressure is its gravity
If you press an object against a wall, the positive pressure is the horizontal component of the force you exert on the object

What is the formula for calculating the pulling force?

It's up to you to calculate the pull
Generally, f = ma
F=umg
Well, there are many more you can go to the website

Moving pulley weight: the heavier the moving pulley, the more friction and rope weight the mechanical efficiency

For the same weight,
The heavier the moving pulley, the lower the mechanical efficiency
The greater the friction, the lower the mechanical efficiency
The heavier the rope, the lower the mechanical efficiency

Calculation formula of mechanical efficiency of fixed pulley, movable pulley and pulley block, with derivation, urgent,

Fixed pulley: w = GH, w = FH, η = GH / FH = g / F
Pulley block: w = GH, w = f × NH, η = GH / (f × NH) = g / FN
Where: G is the weight, f is the pulling force, h is the lifting height of the weight, and N is the number of strands of the load-bearing rope

When a moving pulley is used to lift an object with a weight of 96 n (excluding rope weight and friction), and the pulling force is 60 n, the mechanical efficiency of the moving pulley is 0______ ．

According to the meaning of the question, the useful work w useful = GH, the total work of pulling force w total = FS, for the moving pulley: S = 2h, so η = w useful w total = ghfs = g2f = 96n2 × 60N = 80%, so the answer is: 80%

When a moving pulley is used to lift an object with a weight of 96n (rope weight and friction are not included), the pulling force is 60N. Then the mechanical efficiency of the moving pulley is (). If the pulley is used to lift an object with a weight of 200N, the pulling power is 22.4w when the speed of pulling the rope is (), and the mechanical efficiency is ()

When a moving pulley lifts an object with a weight of 96n (excluding rope weight and friction), the pulling force is 60N, the pulley weight is 60 * 2-96 = 24N, and the efficiency is 96 / 60 * 2 = 80%
If the pulley is used to lift an object with a weight of 200N, the pulling force = (200 + 24) / 2 = 112N, v = P / v = 22.4/112 = 0.2m/s, mechanical efficiency = 200 / 224 = 89.25

A person uses a movable pulley with a weight of 10 N to lift a weight of 150 n. if the movable pulley, rope weight and friction are not taken into account, the tension at the end of the rope is "mechanical efficiency"?
If the rope weight and friction are not taken into account, the tensile force is "mechanical efficiency". If the actual tensile force is 90 n, the mechanical efficiency is "mechanical efficiency"?

If the rope weight and friction are neglected, the tensile force is f = (150 + 10) / 2 = 80N
The mechanical efficiency is η = w / W total = g / 2F = 150 / 160 = 94%
If the actual tension is 90 n, then the mechanical efficiency η '= w you / W' total = g / 2F '= 150 / 180 = 83%