Áp suất là gì? Tổng hợp kiến thức về áp suất từ A-Z

Surely you have heard of atmospheric pressure, osmotic pressure, solid pressure, etc. All of these are unfamiliar terms from when you were in school and are sometimes mentioned. come in everyday life.

Although it is familiar, many of you will not clearly understand what pressure is and issues related to pressure. That's why timhieulichsuquancaugiay.edu.vn has compiled and compiled the content of the article What is pressure? Summary of knowledge about pressure from az in the article below. We invite you to follow along.

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What is pressure?

Understanding pressure helps us understand the definition of pressure.

See the following example: People and cabinets (as illustrated below) always exert a pressure force perpendicular to the floor surface on the floor. Forces like these are called pressures.

Therefore we have the following definition:

Pressure is the force acting on the surface area of ​​an object in a direction perpendicular to the surface under pressure. Pressure is a vector quantity.

The effect of pressure is greater when the pressure is stronger and the area compressed is smaller.

The unit of measurement for pressure is: Newton and is symbolized as N.

Note:

Because the direction (perpendicular to the force-bearing surface) and direction (towards the force-bearing surface) have been determined, when talking about pressure, when people mention pressure, they can only talk about the magnitude (intensity). .

What is pressure?

What is pressure?

When calculating the pressure applied to a surface under great pressure. One must subdivide the force-bearing area and calculate the force acting on that unit area.

Therefore The pressure caused by a solid is the magnitude of the pressure acting on a specified unit area, perpendicular to the pressed surface.

What is pressure symbol?

In physics, pressure has the English name Pressure and is symbolized by the first letter “P”.

Pressure measurement unit

If the unit of pressure is Newton (N), then in the SI international measurement system, the unit of pressure is calculated in Newton per square meter (N/m²).

1 N/m² is called 1 Pascal (Symbol Pa)

So the unit of pressure measurement is called Pascal (Pa) named after French mathematician and physicist Blaise Pascal – who discovered pressure in the 17th century.

1 Pa is very small, it is approximately equal to the pressure of a US dollar on the table.

Pa is the most common pressure measurement unit today. However, in each different geographical area of ​​the world or to serve the calculations of each field with different liquid flows, people use many different pressure measurement units such as PSI (Americas). ), Pa (Asia), Bar (Europe).

To conveniently calculate and use the appropriate pressure measurement unit, we need to convert it to the unit we need. Below is a conversion table of pressure units used by many countries and many industry units.

Write the formula to calculate pressure

The formula for calculating pressure in physics is written as the formula:

In there:

Example of applying the pressure calculation formula

Question C5 (Textbook page 27): A tank has a weight of 340,000N. Calculate the increased pressure of the vehicle on the horizontal road surface, knowing that the contact area of ​​the chain plates with the ground is 1.5m2. Compare that pressure with the pressure of a car weighing 20,000N with an area of ​​250m2 of wheels in contact with the horizontal ground.

Solution instructions:

The pressure of the vehicle increasing on the horizontal road surface is:

P(car)= F/S = 340000/1.5 = 226 666.6 (N/m2)

The pressure of the car on the horizontal road surface is:

P = F/S = 20000/250 = 80 N/cm2 = 800 000 N/m2

So the pressure of the car on the road surface is smaller than the pressure of the car. Therefore, tanks can run on soft ground.

What types of pressure are there and the formula to calculate each type of pressure?

Different pressure gauges are manufactured and calculated to be highly accurate, based on the pressure calculation formula. Let's review with timhieulichsuquancaugiay.edu.vn some of the pressure calculation formulas for each type below.

Formula to calculate solid pressure

The definition and formula for calculating solid pressure are the knowledge we have learned through the examples and explanations above.

The pressure of a solid depends on the contact surface area and weight of the object.

In there:

Formula to calculate fluid pressure

In reality, the liquid exerts pressure in all directions on the bottom of the vessel, the walls of the vessel, and the objects inside it.

Fluid pressure is defined as follows: Fluid pressure is the pressure value on a unit area located at that point.

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The formula for calculating fluid pressure is:

In there:

• P: Is the gas liquid pressure to be calculated (Pa)
• D: Specific gravity of liquid (N/m3).
• H: Height of liquid (m)

Formula to calculate osmotic pressure

Osmotic pressure is the minimum pressure that needs to be applied to a solution to prevent the flow of pure solvent through a semi-permeable membrane toward the solute reservoir.

In physics, osmotic pressure is determined by the following method:

In there:

• P: Osmotic pressure (atm)

• R: Constant (R= 0.082)

• T: Absolute temperature (T = 273 + toC)

• C: Solution concentration (gram/liter)

According to the calculation formula above, we see that the concentration of a solution is proportional to the osmotic pressure of that solution.

Formula to calculate hydrostatic pressure

Hydrostatic pressure is understood as the pressure created by a liquid when it is at rest

In other words, hydrostatic pressure is the pressure calculated when the liquid level is at equilibrium without fluctuations and is calculated according to the formula:

In there:

• P: Hydrostatic pressure of the liquid

• Pa: Atmospheric pressure

• H: Height from the bottom to the static surface of the liquid

• P: default density of a certain liquid unit (Kg/m3)

There is also vacuum pressure, you can see more at: Understanding all about vacuum pressure is the simplest

Devices used to measure pressure

Each different type of pressure will have a dedicated measuring device. Depending on each substance to be measured, we will use separate pressure measuring devices such as: Water, gas, gasoline pressure gauges, etc. Currently, there are 3 commonly used pressure measuring devices:

Pressure gauge

This is a device used to measure the pressure of liquids, gases, vapors… and operates through the impact of water pressure on a moving system that rotates gears to help the watch pointer point to the pressure range on the surface. measuring equipment.

Pressure measuring sensor

When affected by sources such as pressure, heat, etc., the sensor will send the value to the microprocessor, then process it and then output a signal. The device is mainly used to measure pressure in difficult-to-observe locations or in cases where it is necessary to output a signal to control pressure.

The pressure sensor has an electronic clock display

This machine helps users see the pressure right at the time of measurement and at the same time outputs a signal to input to the processor. This is a type of machine that combines an integrated pressure sensor with an electronic display clock face.

If we want to increase or decrease pressure, how do we do it?

How to increase pressure

There are three ways to increase pressure as follows:

• Increase the applied pressure and keep the pressed surface area the same.

• Increase the impact force in the perpendicular direction, while reducing the pressed surface area.

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  Increase the surface area being pressed but keep the pressure the same.

How to reduce pressure

There are three ways to reduce pressure as follows:

• Reduce impact pressure and keep the pressed surface area intact.

• Reduce pressure, while reducing the surface area being pressed.

• Reduce the surface area being pressed but keep the pressure the same.

Example of increasing and decreasing pressure in practice

Some examples of increasing pressure in practice are: nail heads, knives, scissors, straws,… are all pointed to reduce the area being squeezed to increase pressure.

Some examples of pressure reduction in practice are: Rising wheel (to reduce the settlement of an object on the ground, people make this object have a large contact surface).

Application of pressure in practice

• In everyday life, we use pressure cookers for cooking. The two main advantages of a pressure cooker are that it cooks food very quickly and does not lose nutrients in the food. That is an example of gas pressure.

• On cars, people install hydraulic brake systems to slow down and stop the car at the driver's request thanks to understanding liquid pressure.

• For industrial equipment, pressure measurement is indispensable. When measuring pressure, mainly use gauges and are used in industrial applications, in factories, plants, petrochemical refineries, food processing,…

Solving physical pressure exercises for grade 8

Question 1: When measuring the heart's blood pressure, the inflatable cuff of the blood pressure monitor when inserted into the arm should be placed at the same level as the heart. Why?

Solution instructions:

To easily measure heart rate and heart activity that transmits blood to the lungs.

Question 2: A circus performer with a mass of 65kg and wooden chairs with a total mass of 60kg, stacked balanced on a 4-legged chair with a mass of 5kg. The contact area of ​​a chair leg is 10cm2. Calculate the pressure each chair leg exerts on the stage floor.

Solution instructions:

Pressure is evenly distributed to each chair leg:

F = 10.(65+60+5)/4 = 325 (N)

The area of ​​each chair leg is:

S = 10 cm2 = 0.001 m2

The pressure each chair leg exerts on the floor is:

P = F/S = 325/0.001 = 325000 (N/m2)

Question 3: A train car with a mass of 48 tons has 4 iron axles, each axle has 2 wheels, the contact area of ​​each wheel with the rail surface is 4.5 cm2.

a. Calculate the pressure of the train car on the track when the train car is parked on a flat track surface.

b. Calculate the pressure of the train car on the ground if the total contact area of ​​the rails and sleepers on the ground is 2.4 m2.

Solution instructions:

a. Total contact area of ​​the wheels on the rail surface:

S = (4.2) 4.5 = 36 cm2 = 0.0036 m2

The pressure exerted by the train car on the track is equal to the weight of the train car:

F = P = 10 m = 10.48000 = 480000 (N)

b. Pressure acting on train rails:

P = F/S = 480000/0.0036 = 2000000 (N/m2)

Question 4: Place a 60kg bag of rice on a four-legged chair with a mass of 4kg. The ground contact area of ​​each chair leg is 8cm2. Calculate the pressure the chair legs exert on the ground. (Students practice solving this exercise at home.)

Question 5: The student's mass is 40kg, the area of ​​both feet is 4dm2. Calculate the pressure your body exerts on the ground when standing upright. How to double the pressure quickly and simply. (Students practice solving this exercise at home.)

Above is the most complete and detailed knowledge and exercises about pressure. Hopefully the above sharing will help everyone remember the lesson for the longest time. If you find it interesting, please regularly access basic knowledge to update yourself with useful lessons. Don't forget to press the “share article” button below the post to let your friends and acquaintances receive useful value.

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