Ask a few simple questions about physics pressure in junior high school

1: After the water in the closed pot boils, it evaporates out and becomes water vapor, because it cannot be discharged, it accumulates more and more in the pot, and the density of the gas in the pot becomes larger, according to the pressure formula, under the same volume, the pressure is proportional to the density, the volume of gas in the pot remains the same, the density becomes larger, and the pressure will naturally become larger, and the air pressure will increase until the pressure and boiling point reach a dynamic equilibrium. Pressure above one atmosphere is a single finger pressure value, and it is true that it has nothing to do with the outside atmospheric pressure.

2: Please do not understand that the volume of the straw is squeezed small, in this case, assuming that the volume of the straw does not change, because when absorbing water, the deformation of the straw is not large, and a certain amount of gas is sucked out, in fact, under the same volume, the density of the gas in the straw is reduced, which is equivalent to reducing the pressure, so that due to the large external air pressure, the water will be pressed into the straw.

When analyzing the pressure problem, grasp the formula, and pay attention to the density and volume of the gas, and whether there is a change before and after the change is the most important thing.

1.Because of water vaporization. The volume increases, so the air pressure increases. So the boiling point of the water in the pot becomes larger.

1. The pressure cooker uses the principle of thermal expansion and cold contraction, the gas volume increases, and the air pressure increases when the volume of the same space increases.

So the air pressure in a closed pot is not higher than the standard atmospheric pressure. The food needs to be heated at a pressure higher than the standard atmosphere.

2 The straw principle is even simpler. The gas in the straw is squeezed out of a part, so that the volume of the gas in the straw is smaller, the air pressure is smaller, less than the atmospheric pressure, and then the liquid outside is squeezed into the straw by the atmospheric pressure. Do you understand?

Question 1: The pressure of the closed container is independent of atmospheric pressure. The pressure of the gas inside an unclosed container is the same as the standard atmospheric pressure.

Before the pot is closed, the air pressure inside the pot is the same as the outside standard atmospheric pressure.

Then it is closed, heated, and the gas in the pot is heated and expanded, and naturally, the gas pressure in the pot is enhanced, which is higher than the standard atmospheric pressure.

Question 2: One end of the straw is inserted into the water and the other end is in the mouth, so a closed container is formed.

At this time, the water outside the straw is in contact with the outside atmosphere, so the atmospheric pressure on the water is the standard atmospheric pressure.

Before inhaling, the air pressure in the straw is the same as the standard atmospheric pressure outside, so the pressure of the two gases in the straw is the same, so it will not flow.

When inhaling, the volume inside the straw is constant, but the amount of air decreases, that is to say, the air becomes thinner, and the gas pressure naturally decreases as the air becomes thinner (this is the same as the thin air body and the air pressure decreases).

At this time, the pressure of the outside air pressure on the water is greater than the downward pressure of the gas in the straw on the water. So the water is pressed upwards from the straw by the outside air pressure.

Note: The outside atmosphere presses the water in the bottle downward, and the transmission of force actually presses the water in the straw upward. The gas pressure in the straw presses the water in the straw down.

When the balance of the two forces is broken, the water starts moving. When you blow air into the straw, the air pressure in the pipe increases, and the downward pressure on the water in the pipe increases, and the water is blown out, which is also the truth. ）

.Yes...Will be a little deeper.

Gas pressure is essentially the embodiment of molecular thermal motion, it is conceivable that in a plastic bag, there are countless molecules, all of which move irregularly, and finally manifest as a uniform plastic bag in all directions.

For the same volume, the higher the density, the greater the pressure (the higher the number of particles).

In a pressure cooker, water changes from a solid state to a gaseous state, while its volume remains the same, while the particles become more numerous and the pressure increases.

until the pressure is strong enough to open the pressure limiting valve).

2. The volume change is not considered first, because this volume change is pressed up by atmospheric pressure, and the action of suction is causal).

If there is no atmospheric pressure, there will be no such change in volume).

You take in the air, the volume doesn't change, then the density becomes smaller, the pressure becomes less (less than atmospheric pressure) and then the atmospheric pressure can be pressed into the mouth.

1.Which is the greater pressure of the liquid on the bottom of the container?

B large, p= gh].

2.Which is the greater pressure of the liquid on the bottom of the container?

A large, f=ps].

3.Which is the greater pressure of the cup on the table?

B large, p=f s].

4.Which is the most pressure on the tabletop from the cup?

is the same size, f=g].

1.On the right, large p=meat, gh, meat unchanged, g unchanged, h, larger p, larger p2The liquid quality inside is the same, the left side is small at the top, and the bottom is large, so f left, and the right side is large and small, so the right cup + g liquid are unchanged, so f is the same.

f does not change s big p small so p left

1) Careful land = density * volume = kilogram meters * kilograms.

2)f=mg=5*

3) Pressure p = f width s s is the surface of the contact surface between the cube and the ground = square meters.

p=f/s=49/

c p=f s The pressure is half smaller, and the force area is also half smaller, so the pressure is the same.

Still not p, choose c.

The cake can be regarded as a cylinder with uniform density, p = density x g x h, all three are unchanged, so p is unchanged.

The pressure is the ratio of gravity to the load-bearing area, and if you cut half of the piece vertically, the weight is reduced by half, and the load-bearing base area is also reduced by half, and their ratio remains the same.

So it is: c p'=p

Is it a loss to go through?

What is the first stare at: f=500n, s=125cm =p=f s=500npa.

p=40000pa,s=175cm²=

From p=f pin leakage s s to obtain f=ps=40000pa*700n-500n=200n

Something that can carry 200n weight can pass through the ice.

First calculate the maximum pressure that the ice surface can withstand, and then calculate the maximum pressure when the sole is 175, minus 500N

Pay attention to the unit, I personally think that it is enough to use one sole to transport things, because there is always a time when only one shoe hits the ground when people are walking.

It shows that there is pressure everywhere on the bottle wall, and the pressure is small and related to the depth of the liquid, no, the pressure is small and related to the height of the liquid from the liquid level, a (because c has the greatest pressure at the bottom, the water flows out at this point first, but as the water flows out of the bottle, the pressure inside and outside the bottle is unbalanced, the external pressure is stronger than the pressure inside the bottle, and because the water pressure at the following point is strong to flow out, so the air should go in a, so there will be no water out. Finally, it is less than, because the pressure on the container also includes the pressure of air on water, the air has pressure on the water at the liquid level, and the sum of gravity plus the pressure of the air is the pressure on the flat bottom.

(1) The liquid has strong pressure on the side wall of the container.

2) The deeper the depth, the greater the liquid pressure.

3) No, the liquid pressure is only related to the density and depth of the liquid, (4) the atmospheric pressure can support 10 meters of water column (the effect of atmospheric pressure) (5) less than (this question is more complicated, to be answered by the characteristics of the container, the vertical container liquid pressure on the bottom of the container is equal to gravity, generally the plastic bottle is small and large, and the pressure of the liquid on the bottom of the container is greater than gravity).

1.The pressure of the water in the three places is greater than the atmospheric pressure, and the pressure in the C place is the largest, no, because the water pressure in the three places is only related to the water surface of the three places, and has nothing to do with the height of the bottle, a hole, =

The liquid is under pressure on the side walls of the container.

The pressure of a liquid is related to depth.

No, because the depth of the liquid does not change a=

The pressure of the water in all three places is greater than the atmospheric pressure.

Not at c, because the water pressure at the three places is only related to the three places above the water, and has nothing to do with the height of the bottle, =

LGC90 gives a quantitative analysis.

My qualitative analysis came to the same conclusion as his:

The pressure at the bottom of the container filled with water is greater than the pressure at the bottom of the container containing alcohol.

Answer: Originally, the two containers were of the same quality, and the two containers were the same.

Oh, but because the container is >wide at the top and narrow at the bottom< shape. There is an article on this topic.

Think of it this way: Imagine an x liquid that has an extremely high density. How tall is it?

Liquid X only needs to be poured into a small layer of the container to have the same quality as the water and alcohol in the first two containers. Then, the bottom pressure in the third container is px, which can be calculated as px=mx*g s.

The limit method is used here].

Let's compare this px with p alcohol. P alcohol is definitely less than mx*g s, that is, less than px. Why? The reason is that the container is >wide at the top and narrow at the bottom< shape. The side walls of the container containing alcohol share some of the pressure.

Therefore, it is concluded that the pressure at the bottom of the container is related to the mass of the liquid and the distribution of the liquid.

The reason why the pressure at the bottom of the two vessels is different here is because of the change in the distribution of the liquid. In this kind of container, the lower the density of the liquid of the same mass, the lower the pressure on the bottom. Because the lower the density, the larger the volume of the mass condition, the more parts it can adhere to the side wall, thus reducing the pressure on the bottom.

It's been a long time, it's very rusty;

First of all, it is determined that the shape of the container is a regular inverted cone, otherwise it is difficult to calculate;

Set the bottom area S0, the liquid surface area S water, S wine;

vWater = (S0+S) H Water 2;

v wine = (s0 + s wine) h wine 2;

m=ρv；mW=(s0+s) hW2;

m wine = (s0 + s wine) h wine wine 2;

H water water = m water 2 (s0 + s water);

H wine wine = M wine 2 (S0+S wine);

p=ρgh;

p water = g m water 2 (s0 + s water);

P wine = g m wine 2 (S0 + S wine);

m water = m wine;

Since V water is less than V wine, it can be determined that H water is less than H wine, so S water is less than S wine (such as the question, wide mouth container, the higher the liquid level, the larger the liquid surface area);

It can be seen that P water is greater than P wine, that is, the pressure at the bottom of the water is stronger than the pressure at the bottom of the alcohol;

Because the liquid is different from the solid, therefore, the liquid pressure is also different from the solid pressure, on the one hand, due to the action of gravity on the liquid, the pressure is generated on the bottom of the container, on the other hand, the liquid has fluidity, constantly hitting the side wall of the container, in turn, the side wall of the container also exerts a reaction force on the liquid, this reaction force for different shapes of containers, the effect on the bottom of the container is different, for the cylindrical container, this reaction force before and after, left and right cancel each other, and has no effect on the bottom of the container, so the pressure on the bottom of the container is only derived from the gravity of the liquid, i.e. f=g, in this case, p=mg and p=pgh are universal when calculating the pressure on the bottom of the container; However, for the table-shaped container, the reaction force of the pressure exerted by the side wall of the container on the liquid cannot cancel each other, so the pressure on the bottom of the vessel is not only from the gravity of the liquid, but also the resultant force of the reaction force exerted by the wall on the liquid, so f≠g (g is the weight of the liquid).

You have a topic"The mouth is big and the bottom is down"I don't understand.

They have a small pressure on the bottom of the container

p water = density of water * g * height of water (h).

p alcohol = density of alcohol * g * height of alcohol (h).

Because the two lightweight containers A and B are identical, the bottom area of the two containers is equal.

And because v water is less than v alcohol, the height of water (h) is less than the height of alcohol (h), so p water is less than p alcohol.

There are two variables in this question: density and height, which is difficult.

m Water = Density * Volume.

1000*2 10 -3 cubic meters = 2kg

f=g=mg=2kg*

P cup = (F water + F cup) s

Cubic metre. Cubic metre.

19800 Pa.

Total gravity of container + water) The bottom area of the container.

20n+2 10 -3 cubic meters Density of water 10n kg) 2 10 -3 cubic meters.

Hello! According to the liquid pressure formula.

The legs are on the same level as the heart when lying flat, and there is no height difference between them, so the pressure difference is 0

There is a certain height difference between the heart and the legs when standing, and their pressure difference is generated by the height difference of the blood in the human body, so the pressure difference = PGH = cubic meter * 10n kg *