"End of Chapter Summary and Improvement" Pressure PPT

"End of Chapter Summary and Improvement" Pressure PPT

Part One: Key Breakthroughs

Application of p=ρgh

For a solid with a regular shape (that is, the top and bottom are the same thickness), assuming its base area is S, its height is h, and its density is ρ, and it is placed on a horizontal tabletop, the pressure of the solid on the horizontal tabletop can also be calculated using p=ρgh, and is deduced as follows :p=F/S=G/S=ρSgh/S=ρgh.

Typical example: A container is filled with water at a constant speed. The relationship between the pressure p of the water at the bottom of the container and the injection time t is as shown in the figure. This container may be ( )

[Analysis] According to the p-t image, it can be seen that as the water injection time increases, the pressure of the water at the bottom of the container increases, but the increase becomes smaller and smaller. According to p=ρgh, it can be seen that when water is injected into the container at a constant speed, the pressure inside the container will The height of the water surface increases, but the increase becomes smaller and smaller, indicating that the cross-sectional area of ​​the container gradually increases, and item A is consistent with the meaning of the question.

【Answer】A

End-of-Chapter Summary and Improvement PPT, Part 2: Experimental Activities

Experiment 1: Explore the factors that affect the effect of stress

1. Experimental equipment: sand table, small table, hook code, etc.

2. Experimental process

(1) Keep the stress area the same and study the relationship between the pressure effect and the pressure: Make the legs of the small table contact the sand surface and observe the depth of the small table sinking into the sand; then place a 200 g hook code on the table , observe the depth of the small table sinking into the sand.

(2) Keep the pressure the same and study the relationship between the pressure effect and the size of the force-bearing area: make the top of the small table contact the sand surface and observe the depth of the small table sinking into the sand; then make the legs of the small table contact the sand surface and observe The small table sunk deep into the sand.

3.Experimental conclusion

The effect of pressure is related to the size of the pressure and the force-bearing area. The greater the pressure, the smaller the force-bearing area, and the more obvious the pressure effect.

Typical example 1: Xiao Ming uses two objects A and B, weights, foam and other equipment to explore "what factors are related to the effect of pressure", as shown in the picture.

(1) In the experiment, Xiao Ming compared the effect of pressure by observing ______________;

(2) Comparing the experiments shown in Figures A and B, the conclusion that can be drawn is _____________;

(3) If you want to explore "the relationship between the effect of pressure and the size of the force-bearing area", you should compare the experiments shown in Figure __________ and ________;

(4) During the experiment, Xiao Ming cut object B into two pieces of different sizes in the vertical direction, as shown in Figure D. He found that they had the same pressure effect on the foam, from which he concluded that the pressure effect had nothing to do with the stress area. Do you think the problem he has with his inquiry is _____________.

[Analysis] (1) In the experiment, Xiao Ming compared the effect of pressure by observing the degree of depression of the foam; (2) In question pictures A and B, the stressed areas are the same, and the pressure in question picture B is greater, so we get The conclusion is that when the force-bearing area is the same, the greater the pressure, the more obvious the effect of pressure; (3) If you want to explore the "relationship between the effect of pressure and the size of the force-bearing area", you should control the pressure to be the same, and only change The size of the force-bearing area, so the experiments shown in picture A and picture C should be compared; (4) To study the relationship between the pressure effect and the force-bearing area, the pressure should be controlled to be the same, and object B should be cut into pieces in the vertical direction. When two blocks are of different sizes, the stress areas are different and the pressures are also different. That is, the pressures are not controlled to be the same, and the conclusion drawn is wrong.

[Answer] (1) The degree of depression of the foam (2) When the stress area is the same, the greater the pressure, the more obvious the effect of pressure (3) A and C

(4) No control pressure is the same

Experiment 2: Explore the pressure inside the liquid

1. Experimental preparation

(1) Equipment: a cup of water, a cup of salt water, and a simple U-shaped pressure gauge.

(2) Equipment debugging: ① Check the air tightness of the U-shaped pressure gauge, gently press the rubber membrane of the metal box with your hand, and observe whether the liquid column in the U-shaped tube changes significantly; ② Check whether the liquid levels on both sides of the U-shaped tube are at rest If not, the rubber tube needs to be reconnected.

2. Experimental operation

(1) Place the metal box of the pressure gauge into the water at different depths in sequence, and observe the liquid level difference in the U-shaped tube.

(2) Keep the depth of the metal box in the water constant, rotate the direction of the rubber membrane of the metal box, and observe the height difference of the liquid level in the U-shaped tube.

(3) Place the metal boxes at the same depth of clean water and salt water respectively, and observe the liquid level difference in the U-shaped tube.

3.Experimental conclusion

There is pressure in all directions inside the liquid, and the pressure in all directions at the same depth is equal; the pressure of the liquid is related to the density and depth of the liquid. The deeper the depth, the greater the density, and the greater the pressure.

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