"The "Power" of Air" Pressure PPT Courseware 4

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"The "Power" of Air" Pressure PPT Courseware 4

There is pressure inside a liquid in all directions due to the gravity and fluid nature of the liquid.

So, air is also subject to gravity and has fluidity. Is there atmospheric pressure in all directions around us?

Learn about the atmosphere

The earth we live on is a blue planet. Thick gases surround the solid land, nourishing and protecting life on Earth. The thick layer of gas is usually called the atmosphere.

1m3 of air has a mass of 1.29kg. Calculate the mass of the air in your classroom.

In the atmosphere, the air below is pressed by the air above, and the earth is pressed by the entire atmosphere. Air has mass, and under the action of the earth's gravity, it will generate pressure on the area it acts on.

Experiments and Observations

1. Cup-covering experiment

1. Place a piece of cardboard flat on the mouth of a flat glass, hold it down with your hand, and turn it upside down. What will happen after you let go?

2. Fill the glass with water, cover the mouth of the glass with a piece of cardboard, hold it with your hand, and turn it upside down. What will happen after you let go?

3. Slowly turn the mouth of the cup in all directions. What will happen again?

2. Iron barrel “deformation” experiment

3. Experiment on "eating" eggs from a bottle

Light the cotton soaked in alcohol, put it into the bottle, and then plug the mouth of the bottle with a peeled hard-boiled egg. The egg will slowly enter the bottle.

4. Magdeburg Hemisphere Experiment

let's summarize

What inspirations did you get from the above experiments and what conclusions did you draw?

It can be seen that, like liquids, there is pressure in all directions inside the air. This pressure is called atmospheric pressure, or atmospheric pressure or air pressure for short.

atmospheric pressure

1. Cause: Because the air is affected by gravity.

2. Objects immersed in the atmosphere are subject to the pressure generated by the atmosphere.

let me explain

Why can't the two leather bowls be easily pulled apart?

explain:

1. Squeeze out the air in the leather bowl, and the air pressure inside will decrease.

2. The air pressure in the leather bowl is less than the atmospheric pressure.

3. Due to the strong atmospheric pressure, the two leather bowls are pressed together tightly, so the two leather bowls are not easily pulled apart.

Consolidate practice

1. Since the air is also affected by the _____ force and can flow, there is pressure inside the air in the _______ direction.

2. The pressure exerted by the atmosphere on objects immersed in it is called _____________, or _________ for short.

3. The famous ____________ experiment effectively proved the existence of atmospheric pressure. This experiment was conducted by ____________.

4. When the fountain pen absorbs ink, press the spring leaf on the pen a few times. The gas pressure in the pen bladder will be ________. Under the action of ________, the ink will be "sucked" into the rubber tube.

5. Fill the glass with water, seal the mouth of the cup tightly with a piece of cardboard, and carefully turn the cup mouth down so that the paper will not fall off. This is because ( )

A The paper is too light

B The upward pressure of air on the paper is greater than the gravity of water

C The water stuck the paper

D Water is at rest due to inertia

changes in atmospheric pressure

The magnitude of atmospheric pressure is not static. It is related to altitude. The higher the altitude, the smaller the value of atmospheric pressure.

People usually call the pressure generated by 760mm of mercury 1 standard atmosphere.

One standard atmospheric pressure = 1013hPa (hundred Pascals)

1. Why does the higher the altitude, the smaller the atmospheric pressure?

The higher you are from the ground, the thinner the air and the lower the atmospheric pressure there is.

2. It is generally believed that for every 12m increase in altitude, the value of atmospheric pressure decreases by 1mm (133Pa) of mercury.

3. If we know the altitude of a certain place, we can know the air pressure value at this altitude through comparison; conversely, as long as we measure the atmospheric pressure value of a certain place, we can also know the approximate altitude of this place. So the barometer can be converted into an altimeter.

barometer

① Advantages of mercury (mercury) barometer: accurate measurement, but inconvenient to carry.

②The empty box barometer is also a commonly used barometer. Its advantage is that it is easy to carry, but it is not as accurate as a mercury barometer.

③Tubular spring pressure gauge

In addition to measuring atmospheric pressure, air pressure measurements in car tires, aircraft wheels, and space stations also require barometers. Tubular spring pressure gauges are commonly used.

One end of the hollow spring tube in the tubular spring pressure gauge is connected to the measured gas, while the other end is closed and connected to levers, gears, pointers, etc. When the pressure in the hollow spring increases, the tube tends to straighten, that is, the curvature becomes smaller. With this change in shape, the lever and gear drive the pointer to indicate the pressure of the measured gas.

Consolidate practice

1. Among the following phenomena, the existence of atmospheric pressure cannot be explained ()

A. Plug the small hole in the lid of the teapot so that the water in the teapot cannot be poured out easily.

B Use a straw to suck the juice in the cup into your mouth

C Torricelli experiment

D lock

2. When using a fountain pen to absorb ink, just press and release the spring leaf a few times, and the ink will be absorbed into the rubber tube. This is because ( )

A The rubber tube has suction C The effect of atmospheric pressure

B The spring leaf has suction. D The vacuum in the rubber tube has suction.

3. Do the Torricelli experiment at a standard atmospheric pressure. If a small hole is made at the top of a glass tube, the mercury column inside the tube will ( )

A. Spray upward

B. Slightly lower

C. Lower to the level of the mercury surface outside the tube

D. Keep the original height unchanged

Expand your thinking

Are there any other ways to measure atmospheric pressure?

As shown in the picture: Place the suction cup of the water-soaked plastic hook on a smooth horizontal plate and squeeze out the air inside. Use a spring dynamometer to hook the hanging hook and slowly pull it up until the suction cup comes off the board. Write down the reading of the spring force gauge when it is just separated. This is the pressure F of the atmosphere on the suction cup. Try to measure the contact area S between the suction cup and the tabletop, and calculate the atmospheric pressure!

The atmospheric pressure was so strong, why didn't the house collapse?

Because there is atmosphere inside the house, the pressure of the atmosphere inside and outside the house is equal and opposite, so the house will not collapse because there is air inside.

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Update Time: 2024-11-22

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