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, … all are the terms that are no strangers from the time when sitting on the school chair and sometimes reminded. Come in everyday life.

Although familiar, there will be many friends who do not clearly understand what the pressure is and the issues related to pressure. That’s why Nguyễn Tất Thành has summarized and compiled the content of the pressure article? Summary of knowledge about pressure from AZ in the article below. Invite you to follow.

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What is pressure?

Understand the pressure helps us to understand what pressure definition is.

See the following example: People and cabinets (as shown below) always act on the floor a force of the square is perpendicular to the floor. Forces like this are called pressure.

So we have the following definition:

The pressure is the force on the surface area of ​​an object perpendicular to the pressure surface. The pressure is the vector quantity.

The greater the effect of the pressure as the stronger the pressure and the smaller the area is forced.

The measurement unit of the pressure is: Newton and is denoted N.

Note:

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

What is pressure?

What is pressure?

When calculating the pressure is acting on a large pressure surface. People must split the bearing area and calculate the force impact on the unit area.

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

What is the symbol pressure?

In physics, the pressure with English name is pressure and signed by the first letter “p”

Pressure measurement unit

If the unit of pressure is Newton (n), in the international Si measurement system, the unit of the pressure is calculated in Newton in a square meter (N/m²).

1 n/m² is called 1 pascal (pa symbol)

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

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

PA is the most common pressure measurement unit today. However, in each different geographical area in the world or to serve the calculation of each field with different fluid lines, people use many different pressure measurements such as PSI (America. ), PA (Asia), Bar (Europe).

For convenience and use of the appropriate pressure measurement unit, we need to convert to the unit we need. Below is a table of conversion of pressure units used by many countries and many units in the industry.

Write down the pressure formula

The formula for calculating the pressure in physics is written in the form of the formula:

In there:

Example application formula for pressure calculation

Sentence C5 (textbook page 27): A tank weighs 340000N. Calculate the pressure of the tank on the horizontal road surface, knowing that the area of ​​contact with chains with soil is 1.5m2. Compare that pressure with the pressure of a car weighing 20,000N with the area of ​​wheels in contact with the horizontal ground of 250m2.

Solution instructions:

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

P (vehicle) = f/s = 340000/1.5 = 226 666.6 (n/m2)

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

P = f/s = 2000/250 = 80 n/cm2 = 800 000 n/m2

So the pressure of the tank on the road surface is smaller than the car’s pressure. Therefore the tanks can run on soft soil.

There are types of pressure and the formula for calculating each type

Different pressure gauges are produced and calculated to get high accuracy, based on the pressure formula. Let’s take a look at some of the pressure formulas of each type below.

Formula for calculating solid pressure

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

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

In there:

Formula for calculating liquid pressure

In fact, the liquid causes pressure in all directions to the bottom of the jar, the wall and the objects in its heart.

The liquid pressure is defined as follows: Liquid pressure is the pressure value on a unit of area placed at that point.

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The formula for calculating liquid pressure is:

In there:

• P: is the pressure of gas liquid to be calculated (PA)
• D: Density of liquid (N/m3).
• H: The height of the liquid (m)

Formula for calculating osmotic pressure

The osmotic pressure is the minimum pressure that should be applied to the solution to prevent the flow of pure solvent through the semi -absorbent membrane towards the solute container.

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 above formula, we see: The concentration of the solution is proportional to the osmotic pressure of that solution itself.

Formula for calculating hydrostatic pressure

The hydrostatic pressure is understood as the pressure generated from the liquid when standing still

In other words, hydrostatic pressure is the pressure calculated when the liquid ink is at equilibrium without oscillation and is calculated by the formula:

In there:

• P: hydrostatic pressure of liquid

• PA: atmospheric pressure

• H: The height from the bottom to the static face of the liquid

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

There is also a vacuum pressure, you can see more at: Understand all the simplest vacuum pressure

Devices used to measure pressure

Each different type of pressure will have special measuring devices. Depending on each substance, we will use its own pressure measuring device such as: Water pressure, gas, gasoline, … Currently, there are 3 commonly used pressure gauges:

Pressure meter

This is a device used to measure the pressure of liquids, gas, steam … and operate through the impact of water pressure on the movement system to rotate the gear to help the needle point the clock pointing to the pressure range on the face measuring device.

Pressure measurement sensor

When affected by sources such as pressure, heat, … the sensor will bring the value to the processor, then process and then signal. The machine is mainly used to measure the pressure of difficult positions or cases where the signal is needed to control the pressure.

Pressure measurement sensor is present to display electronic clock

This machine helps users see the pressure right at the time of measurement and at the same time exporting the signal to put into the processor. This is the type of machine combined with a pressure measurement sensor integrated with an electronic display clock face.

If you want to increase and decrease the pressure, how do we do it?

How to increase pressure

There are three ways to increase pressure as follows:

• Increase the pressure and keep the surface the pressed surface.

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

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  Increasing the surface area is pressed but remains the same pressure.

How to reduce pressure

There are three ways to reduce pressure as follows:

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

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

• Reduce the surface area is pressed but remains the same pressure.

Examples of actual increase and decrease in pressure

Some examples of increased pressure in fact are: nail heads, knives, scissors, straws, etc. are pointed to reduce the area forced to increase pressure.

Some examples of reducing pressure in fact are: Tank wheels (to reduce the subsidence of the object on the ground, people make this object with large contact).

Application of pressure in reality

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

• In the car, people installed hydraulic brakes to reduce speed and stop at the driver’s request thanks to the knowledge of liquid pressure.

• For industrial equipment, the pressure measurement is indispensable. When measuring the pressure mainly using the meter and is used in industrial applications, factories, factories, petrochemical filters, food processing, …

Solving 8th grade physical pressure exercises

Question 1: When measuring the blood pressure of the heart, the inflatable cuff of the blood pressure monitor when inserted on the hand should be horizontal with the heart position. Why?

Solution instructions:

To easily measure the heart rate and activity of the heart transfusion to the lungs.

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

Solution instructions:

The pressure is evenly distributed for 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 of each chair leg acts on the floor is:

P = f/s = 325/0.001 = 325000 (n/m2)

Question 3: A 48 -ton trained train has 4 iron wheels, each with 2 wheels, the contact area of ​​each wheel with a rail is 4.5 cm2.

a. Calculate the pressure of the train to the tracks when the train is parked on the surface of the rail.

b. Calculate the pressure of the train to the ground if the total area of ​​rail contact and the sleeper on the ground is 2.4 m2.

Solution instructions:

a. The total contact area of ​​the wheels on the rail face:

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

Pressure due to the car carried down on the track is equal to the weight of the train:

F = P = 10 m = 10,48000 = 480000 (n)

b. Pressure works on train rails:

P = f/s = 480000/0.0036 = 200000 (n/m2)

Question 4: Put a bag of 60kg rice on a four -leg chair with a weight of 4kg. The area of ​​contact with the ground of each chair leg is 8cm2. Calculate the pressure of the foot legs acting on the ground. (Students self -practice this exercise at home.)

Question 5: The student’s mass is 40kg, the area of ​​both feet is 4Dm2. Calculate your body’s pressure on the ground when standing upright. How to increase the pressure doubled quickly and simply. (Students self -practice this exercise at home.)

Above is the knowledge and exercises about the most complete and detailed pressure. Hopefully the above sharing will help people to remember the lesson for the longest way. If you find it interesting, often access the basic knowledge to be able to update yourself with useful lessons. Do not forget to press the “Share article” button below the post for friends as well as acquaintances to get useful value.

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