Why do paper towels don t get wet when poured in water in a cup?

1.This is because there is no air inside the cup, and there is time gas on the outside of the cup. The air has atmospheric pressure. This pressure presses the paper and holds the water in the cup, so that the water does not flow out.

2.The process of the experiment was as follows: first fill a cup with water, and then gently spread a piece of paper on top of the cup.

But be careful, don't break the paper, and don't spill the water. When this is done, turn the cup upside down, not diagonally, vertically. Then remove your hand.

At this time, you will notice that a very thin piece of paper holds up a glass of water, and the water does not come out.

Because the rim of the cup is covered with paper, air flow from the outside world does not enter the cup when the cup is turned upside down. At this time, the pressure of the outside atmosphere is higher than the pressure of the water on the paper, so the water does not flow out easily. If the cup is filled with water, there is no air, so if you cover the cardboard and turn it upside down, you can think that the cup filled with water has the same characteristics as the cup with vacuum.

This phenomenon occurs when the paper is stuffed at the bottom of the cup, and when the cup is upside down on the horizontal plane, the edge of the cup touches the water surface at the same time, and the paper ball does not fall off.

Because the air is enclosed in the cup, the water does not rise to the bottom of the cup.

There is air in the cup. When the cup enters the water, the air in the cup is compressed. When the pressure is equal to the buoyancy of the water, the water does not enter the cup again. So the pulp at the bottom is not wet. But only if the paper towel completely seals the cup.

When there is a piece of paper, the piece of paper has a vertical upward support force for the water due to the atmospheric pressure. However, when the paper is removed, the interface between water and air is not horizontal and flat, so the direction of the force of atmospheric pressure on water in different parts is different, so the water falls. In the case of a very small cup (think of a very thin tube), water will not flow out without a piece of paper, because the water and the air form a horizontal and nearly flat interface; With the increase of the mouth of the cup, the water due to the joint action of its own gravity and tension, the water-air interface will gradually protrude downward to form a spherical surface, when the mouth of the cup increases to a certain extent, the tension and atmospheric pressure can not reach the balance with gravity, so the interface is destroyed, and the water in different parts receives atmospheric pressure in different directions, thus flowing out.

It's the air pressure that puts the paper towel on top of it, so it can't come into contact with water.

The paper towel covers the water cup and the water does not flow, which uses the principle of pressure. Because the rim of the cup is covered with paper, air from the outside world does not enter the cup when it is upside down. At this time, because the pressure of the outside atmosphere is much greater than the pressure of water on the paper, therefore, the water will not flow out.

The ratio of the magnitude of the pressure on the object to the area of the force is called the pressure, and the symbol is p. Pressure is used to compare the effect of pressure next to orange Ming, the greater the pressure, the effect of pressure.

The more obvious. According to the molecular kinetic theory, the rounding rubber strength of the gas is generated by the frequent collision of a large number of molecules with the container wall. The collision time of a single molecule on the container wall is extremely short, and the effect is not continuous, but a large number of molecules frequently collide with the vessel wall, and the force on the vessel wall is continuous and uniform, and the ratio of this pressure to the area of the vessel wall is the pressure strength is small.

The change in atmospheric pressure is related to altitude. Atmospheric pressure is determined by the atmosphere.

Created by gravity, the higher above the ground, the thinner the atmosphere, and the lower the atmospheric pressure should be. However, due to the density of the air in relation to the gravitational force on the atmosphere.

The change with altitude is not uniform, so the atmospheric pressure is also uneven as it decreases with altitude. Atmospheric pressure varies with altitude.

Decreases with increasing height.

There are three main reasons:

1. Because there is no air in the cup, the atmospheric pressure in the cup = 0.

2. Atmospheric pressure has no direction, that is to say, it exists in any direction, so the atmosphere below the cup has an upward support force.

3. At this moment, the upward atmospheric pressure on the paper covered by the mouth of the cup is greater than the gravity of the water in the cup.

The scientific principle is that the piece of paper is in a state of force equilibrium at this time.

The paper piece is subjected to the pressure of its own gravity and the gravity of the water in the cup, and these two forces form a combined land force f1 in a vertical downward direction. Depending on the surface tension of the water, the paper is subjected to an upward pulling force. Since the piece of paper is in the atmosphere, the piece of paper is also subjected to atmospheric pressure, which is vertically upward, forming a resultant force f2 with the tensile force.

F1 and F2 are equal in magnitude and opposite directions, so the forces are balanced. Because the paper is affected by the surface tension of the water, it is completely closed in close contact with the mouth of the cup, so the paper continues to maintain the balance of force, and naturally keeps the water in the cup and the water will not leak out.

Regarding why the water does not leak into the cup when a piece of paper is put in the cup, the paper towel covers the water cup and the water does not flow is based on the principle of pressure. Because the rim of the cup is covered with paper, air from the outside world does not enter the cup when it is upside down. At this time, the pressure of the outside atmosphere is much greater than the pressure of the water on the paper, so the water will not flow out.

The ratio of the magnitude of the pressure on the object to the area of the force is called the pressure, and the symbol is p. Pressure is used to compare the effect of pressure, and the greater the pressure, the more obvious the effect of pressure.

Pressure is a physical quantity that expresses the magnitude of the pressure experienced by an object per unit area. The standard atmospheric pressure is the amount of atmospheric pressure that is equivalent to the pressure generated by a column of mercury of about 76 cm (760 mm). The effect of pressure is not only related to the amount of pressure, but also to the area of force.

When the force area is the same, the greater the pressure, the more obvious the effect of the pressure. When the pressure is the same, the smaller the force area, the more obvious the effect of the pressure action. The air is subject to gravity, and the air is fluid, so there is pressure inside the air in all directions, and this pressure is called atmospheric pressure.

Because there is atmospheric pressure

When the paper is in close contact with the water return, the atmospheric pressure inside the cup is 0

The air pressure of the limb with a large leakage cavity in the outside is so, so it can hold the paper down.

The paper is subjected to the pressure of its own gravity and the gravity of the water on the cup, and these two forces form a vertical downward resultant force f1. The surface tension of the water subjectes the paper to an upward tension and a vertical upward atmospheric pressure.

The paper mill is subjected to the pressure of its own gravity and the gravity of the water on the cup, and these two forces form a vertical downward net force f1. The surface tension of the water causes the paper to be subjected to an upward tension and a vertical upward atmospheric pressure, forming a resultant force equal to the magnitude of f2 and the opposite direction of the square disturbance, so the force is balanced. So keep the water in the cup and the water won't leak out.

The paper is subjected to the pressure formed by the gravity of the paper itself and the gravity of the water on the cup, and the two forces form a vertical downward combination.

zhi force f1. The surface tension force of the water causes the paper to be subjected to an upward tension force and a vertical upward atmospheric pressure, forming a resultant force equal to the magnitude of f2 and opposite in the direction, so the force is balanced. So keep the water in the cup and the water won't leak out.

The cup filled with water is full of water pressure, and there is no atmospheric pressure, so it does not flow out.

There is atmospheric pressure outside, and the inside of the cup is full of water, and the atmospheric pressure is against the water, so it will not fall.

When filling with bai water and covering and then standing upside down, the cup is full of water, which is quite zhi dao vacuum, so the top of the paper (inside the cup) has no atmospheric pressure only water pressure, and the lower part of the paper is atmospheric pressure much greater than the water pressure, so it will not flow out.

As an aside, when poking a small hole, because the tension of the water (which can be understood as maintaining the minimum surface area) is greater than the atmospheric pressure, the air still cannot enter the cup, so the cup is still in a vacuum state, and the water still does not flow down.

When the hole is large enough or when the paper is taken away, the tension of the water is basically the same, and the atmospheric pressure increases (depending on the area of contact between the water and the air), and the air can enter the cup, so the water will flow down.

Because the gravity of the cup, quilt and water thinned into pressure. It won't leak yet.

Why do you all know that?

I've done experiments, but.

I don't think it's scientific!

There is atmospheric pressure so the water does not.

The paper is placed on top of the water cup and does not get wet when turned upside down, because of the pressure. Stuff the paper towel into an empty water cup to make sure it doesn't fall off, then turn the water cup upside down and slowly put it in a basin or bucket and you will find that the paper won't get wet. This experiment was very interesting and surprised many people.

The following elaborates on "why the paper will not get wet when it is turned upside down on the cup", and interested friends can continue to read to understand how to do it.

1. Principle: pressure. The paper does not get wet when placed upside down on a water cup, and the principle of pressure is used.

2. Reason: After the water cup with paper towels enters the water, the Xinhuhu air in the cup has been compressed, and when the air is compressed to the same level as the buoyancy of the water, the water will not continue to enter the cup, and the paper towel at the bottom of the cup will not be wet.

3. Experimental method: knead a paper towel into a small ball, put it in a dry cup to ensure that the paper towel will not fall out, and then turn the cup upside down and slowly put it into a basin or bucket.

4. Precautions for experiments: (1) The water level should not exceed the cup. (2) When putting the cup into the basin or bucket, the movement should be lighter and slower.

<> napkins can cover a glass of water is using the principle of physical medium pressure. When the water soaks the mouth of the water cup, the outside air cannot enter the cup, at this time, the outside atmospheric pressure is greater than the pressure of the water on the paper, so the napkin can cover a glass of water. By reading the above specific introductions to "why paper doesn't get wet when placed on a water cup" and "why napkins can cover a glass of water", I hope it can provide you with a reference.