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In a bathing beach, the bottom of the water is full of stones. In the process of swimming from deep water to shallow water, the following experience and analysis are reasonable () A. Feet are getting more and more painful because water has less and less support for people. B. feet are getting more and more painful because people are receiving more and more gravity. C. feet don't hurt because people are getting lighter and lighter. D. feet don't hurt because water has more and more support for people
When people move from deep water to shallow water, the volume of discharged water decreases. According to Archimedes' principle, people's buoyancy decreases. At this time, people are affected by their own gravity g, buoyancy F of water and supporting force F of stone, and are in a state of balance in the vertical direction, so f = G-F floating. Because buoyancy decreases and gravity remains unchanged, supporting force increases, so people's feet will hurt more and more So a
Many physical tests can be done by using the objects around you. Now put the two glass mouths on the same horizontal plane, and the distance between the two cups is about 1cm. Put the table tennis ball into one of the cups, and hold the cup firmly with both hands (as shown in the figure). Blow hard between the two cups, and the table tennis ball will______ What is the basis of your judgment______ ．
When blowing air from the cup mouth, the air flow velocity at the cup mouth is high, the pressure is low, and the air flow velocity at the bottom of the cup is low, the pressure is high. Under the effect of pressure difference, the ping-pong ball moves closer to the cup mouth under the effect of pressure difference. So the answer is: move closer to the cup mouth; the higher the gas flow velocity, the lower the pressure
When a solid wooden ball and an iron ball of equal volume are put into water at rest_______ The buoyancy of the ball is greater; when the solid wood ball and iron ball with equal mass are at rest, the volume V (wood) of mercury is separated____ V (iron) (fill; =)
Please explain the solution
2 is not about buoyancy
In relay race, if the hand over is as fast as the receiver, he can catch the baton by "seeking stillness in motion"_________________________ It's the cause of the disaster
1. The first question is iron ball. Because the wooden ball floats and the iron ball sinks at the bottom of the water, the volume of the iron ball is relatively large and the buoyancy is naturally large
Second question = because the density of iron and wood is less than mercury, they both float, so the buoyancy is equal to their own gravity. If the mass is the same, the gravity is the same
2. They are relatively static
W useful = GH this G is the gravity of the object, what is h? Is it the height of the object?
Wtotal = FS, is f the force at the free end or the force on the object
S = NH, s is the moving distance of the object, n is the number of ropes, h is the height of the free end or the moving height of the object
How dizzy
W = GH is the height of the object
Wtotal = FS, f is the force at the free end
S = NH (wrong drop) if s is the moving distance of the object and N is the number of ropes, then h is the moving distance of the free end. In this case, the expression should be s = (1 / N) H (why to use 1 / N can be consulted in the future)
Note: the number of ropes tied on the movable pulley (whether it is in or out) is n
The formula of mechanical efficiency and work in Physics
Formula: w = FS principle of work: content: when using machinery, the work done by people will not be less than the work done directly by hand; that is: using any machinery will not save work
Physical pulley and mechanical efficiency
When a moving pulley is used to lift a heavy object, the tension at the free end of the rope is 600N, regardless of friction. 2. When the moving pulley is used to lift 2000N object B, what is the tension of the rope and what is the mechanical efficiency
There are three pieces of rope in Figure A and two pieces of rope in Figure B. It is more labor-saving in Figure a
The mechanical efficiency formula you use is right = GH / Fs, GH is the same, s a is greater than S B, yes, but f a is less than F B, FS is equal
The formula of mechanical efficiency is also equal to that of g / (G + G)
Answer D
In addition, the mechanical efficiency is only related to the weight of the material and the heavy friction of the pulley, and has nothing to do with the rope winding method
Is that ok?
Some physics problems in grade two of junior high school (about pulley)
1. There are two kinds of pulley: fixed pulley and movable pulley. Fixed pulley can't be used (), but it can change the direction of force
2. Among the following simple machines, the one that must not save labor is ()
A lever B pulley block C movable pulley D fixed pulley
3. When using the pulley block, the force to lift the weight depends on ()
A number of fixed pulleys B number of movable pulleys C number of fixed pulleys and movable pulleys d number of sections connecting movable pulleys
4. Use pulley block to lift goods weighing 2400N at a uniform speed, regardless of friction and pulley gravity. If the downward force is 600N, the pulley block shall be composed of () fixed pulley and () movable pulley. There are () ropes on the pulley block bearing gravity
5. In the case of neglecting the self weight and friction of the machine, the simple machine that can't lift a 30n object with 15N pulling force is ()
A a movable pulley B a fixed pulley C lever d a fixed pulley and a movable pulley block
6. Use pulley block. When the weight is raised by 0.6m, the free end of the rope is pulled down by 3M, which changes the direction of power. Please design a pulley block that meets the requirements and draw the winding method
1. Labor saving
2、D
3、D
4. 1 fixed pulley, 2 movable pulley, 4 pieces
5、A
6. Two movable pulleys and two fixed pulleys. Because they are five sections of rope, the rope is wound from the fixed pulley
As shown in the figure, the weights of the two objects are G1 and G2 respectively. Ignoring the self weight and friction of the pulley, when the pulley is balanced, what is the ratio of G1 to G2?
Picture:
T1, T2 and T3 are set from left to right
T1=T2=T3
G2=T2+T3
Problems in physics of grade two
No matter how many pulleys are used to pull a person up and down the balcony, the minimum number of pulleys is 700 Newton, and the maximum number of pulleys to lift a person up and down the balcony is 700 Newton
A pulley block is composed of a movable pulley and a fixed pulley. The starting end of the rope is fixed on the fixed pulley, and then the rope is wound around the fixed pulley, and the tail end of the rope is pulled upward after being wound around the movable pulley
There is an object a with a volume of 0.1m3 and a density of 8000kg / m3. If the pulley block is used to make it move horizontally to the left at a uniform speed of 2m / s, the sliding friction force is 294n, the hand pull force is 105N, and the pulling power of the pulley block is 84
Drawing the configuration diagram of pulley block requires the least number of pulleys
Distance of pulling rope in 5S
Mechanical efficiency of pulley block
From P = FV to v = P / F = 84w / 105N = 0.8m/s
N = 0.8m/s/0.2m/s = 4 strands, so at least three pulleys are required
Distance of pulling rope within 5S: 0.8m/s * 5S = 4m
Mechanical efficiency: 294n * 0.2m/s
___________ ==70%
105N*0.8m/s
RELATED INFORMATIONS
- 1. buoyancy A and B are liquid and solid respectively. The density of liquid a is 1g / cm3, and that of solid B is 0.5g/cm3. When a solid solid (composed of substance B) with a volume of 10-3m3 is put into a container containing enough liquid of substance A, how much buoyancy does the solid solid receive when it is still? How much volume does the liquid displace?
- 2. All formulas of buoyancy Buoyancy knowledge explains all the variant formulas of buoyancy
- 3. The meaning and calculation formula of 1 ＼ G 2. On buoyancy formula
- 4. The formula of buoyancy
- 5. 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)______ ．
- 6. Typical problems in junior high school physics
- 7. As shown in the figure, a piece of lead is hung under an inflated balloon with a thin thread, put it into the water, and it is just in a static state somewhere. If some water is slowly released from the bottom, the lead and the balloon () A. Still able to stand still B. move down C. move up D. stand still. It's possible to move up or down
- 8. 1. The buoyancy of a small ball with a volume of 2x10 cubic meters and a volume of negative cubic meters is - Niu if it is completely immersed in water. If half of its volume is immersed in water, the buoyancy is - Niu 2. When the gravity of the metal block is 26.5n and the metal block is suspended by a spring scale and immersed in water, the indication of the spring scale is 16.7n. The buoyancy of the metal block under water is - n 3. An object weighing 4 N, with a volume of 0.5 cubic decimeter, will be completely immersed in water, and the buoyancy it receives is - cow, it will lose weight in water—— 4. If a piece of wood weighs 20n and floats on the surface of the water and is still, the buoyancy of the piece of wood to the water is - Niu 5. An ocean going ship sailed into the Huangpu River from the East China Sea. The ship realized the buoyancy it received
- 9. How is the buoyancy formula derived?
- 10. How to deduce the formula of buoyancy?
- 11. Who listed the related formulas of physical pressure and buoyancy one by one, including Rou = m / V, which is not published in textbooks? Don't take too many words to explain in front of me. Just tell me what the physical quantity is. I want to copy and paste it
- 12. A course of junior high school physics [pressure and buoyancy], This is the physical simulation of Haidian District in Beijing in 2009 As shown in the figure (a cylindrical container contains a plastic box, in which an iron block floats on the water surface), the cylindrical container with bottom area S1 contains liquid with unknown density. Put a cube metal block with density ρ into the rectangular plastic box with bottom area S2 (the thickness of the plastic box can be ignored), The plastic box floats on the liquid surface (the liquid will not overflow the container), and its immersion depth is H1. If the metal block is taken out of the plastic box, it is tied under the plastic box with thin wire, and put into the liquid, the metal block does not contact the container, and the immersion depth of the plastic box is H2. Cut the thin wire, the metal block will sink to the bottom of the container, and the plastic box floats on the liquid surface, The depth of immersion is H3. If the plastic box is always upright without inclination, the pressure of the liquid on the bottom of the cylindrical container is reduced before and after the thin line is cut? Two supplementary points: 1. The density of the liquid in the container is unknown, and the expression should not contain ρ liquid. 2. The question is how much pressure has been reduced. Not why.
- 13. All the formulas for buoyancy and pressure
- 14. When measuring the density of a small solid object, a physics interest group adopted the following experimental operations: first, the mass mo of the object was measured with a balance; then, a certain amount of water was put into a small beaker, and the total mass M1 of the beaker and water was measured with a balance; then, after the object was tied up with a thin line, the mass M1 of the beaker and water was measured, The object is immersed in the water of the beaker (the water does not overflow and the object does not touch the beaker) by holding a thin line in hand. At this time, the measured value of the balance is m2, as shown in Figure 6 A. The buoyancy of an object in water is MOG B. The buoyancy of an object in water is (m2-ml) g C. The density of the object is Mo / m2-m1 * P water D. The density of the object is Mo / m2-m0 * P water 、 I don't understand at all. I'm going to take the senior high school entrance examination right away. It's really disturbing that I don't understand
- 15. Some questions about buoyancy in junior high school physics 1. A 100 cubic centimeter object is hung under the spring dynamometer. When the object is immersed in water, the indication of the spring dynamometer is 1.7n__ N 2. Put a solid aluminum block with a mass of 27g into a beaker filled with water. When the aluminum block is still in water, the mass of water discharged from the beaker is__ g. Put the aluminum block into a beaker filled with alcohol, and the mass of the discharged alcohol is__ g
- 16. Under what conditions is f floating = ρ liquid GV discharged, under what conditions is f floating = g discharged, f floating = m discharged, G discharged
- 17. The physical meaning of G = 9.8n/kg is______ ．
- 18. What's the meaning of ml / dl? How to read it? What's the difference between ml / dl and Mg / dl
- 19. Conversion of kg and Mg 72kg = 10 to the seventh power mg
- 20. What is Archimedes' formula of buoyancy principle An object is subjected to upward buoyancy, which is equal to the gravity of the liquid displaced by the object!