Presentation on the topic “Pascal’s Law. Pressure in liquids and gases
Questions 1. What properties of gases distinguish them from solids and liquids? Answer: Gases do not have their own shape and constant volume. They take the shape of a vessel and completely fill the volume provided to them. 2. How is gas pressure explained based on the theory of molecular motion? Answer: Gas pressure on the walls of blood vessels is caused by impacts of gas molecules. 3.Why does gas pressure increase during compression and decrease during expansion? Answer: The number of molecules in each cubic centimeter increases with compression (decreases with expansion), and this causes the number of impacts on the walls of the vessel to increase (decreases). Therefore, pressure increases with compression and decreases with expansion. 4. In what state does the gas produce greater pressure: cold or heated? Answer: The higher the temperature of the gas, the higher the gas pressure in a closed vessel. 5.Why are compressed gases contained in special cylinders? Answer: Compressed gases exert enormous pressure on the walls of the vessel, so they have to be enclosed in special durable steel cylinders.
Pascal Blaise () Discovered and studied a number of important properties of liquids and gases. Experiments confirmed the existence of atmospheric pressure, discovered by the Italian scientist Torricelli.
Plan for studying a physical law 1. Mathematical notation and verbal formulation. Mathematical notation and verbal formulation. 2. Experienced confirmation. Experienced confirmation. 3. Theory explaining the law. Theory explaining the law. 4. Limits of applicability. 5. The practical significance of the law and the scope of its application. The practical significance of the law and the scope of its application.
THEORY EXPLAINING THE LAW THEORY EXPLAINING THE LAW The physical content of this law is that the molecules of a liquid or gas are very mobile. They are always distributed fairly evenly throughout the entire volume, and any external pressure can only change the concentration of particles, but the uniformity in their distribution remains. Only at the initial moment, for example, when the volume of gas decreases, its density will be greater in the piston area, but due to the random movement of molecules, the concentration levels out very quickly.
Practical significance of Pascal's law The figure shows the device of a pneumatic brake of a railway car. Line 1, brake cylinder 4 and reservoir 3 are filled with compressed air. When the stop valve is opened, compressed air comes out of the main pipe. And the pressure in the right part of the brake cylinder becomes less than in the left (from which compressed air cannot escape thanks to valve 2). As a result of this, the piston of the brake cylinder moves to the right and presses the brake pad 5 to the rim of the wheel 6, which is then braked.
Practical significance of Pascal's law The structure of a jackhammer is shown in the figure. Compressed air is supplied through hose 1. Device 2, called the spool, directs it alternately to the upper and lower parts of the cylinder. Under the influence of this air, the striker 3 begins to quickly move in one direction or the other, periodically affecting the peak 4. The blows of the latter are used to loosen frozen soils, break off pieces of rocks and coal from the massif.
- Municipal educational institution "Krasnovidovskaya basic secondary school" of the Krasnovidovsky rural settlement of the Kamsko-Ustinsky municipal district of the Republic of Tatarstan
- Lesson in physics in 7th grade on the topic “Gas pressure
- Transmission of pressure by liquids and gases.
- Pascal's Law"
- Physics! What a capacity of words!
- Physics is not just sound for us!
- Physics - support and basis
- All sciences without exception!”
- 2. How will the pressure of a gas change if it is heated at a constant volume?
- a) will not change; b) will become more; c) will become smaller.
- 3. The rubber ball was squeezed by hands and deformed. Has this changed:
- mass – weight – volume – density – pressure- air in it? (Write yes or no.)
- 4. The gas in the vessel exerts a pressure of 300 Pa on the left wall. What pressure does the gas produce on the bottom, top and right walls of the vessel?
- a) on the bottom 400 Pa, on the top 300 Pa, on the right 200 Pa; b) on the bottom 300 Pa, on the top 100 Pa, on the right 400 Pa; V) .
- 5. The main reason for gas pressure on the walls of a vessel is
- A) ; b) little mutual attraction of gas molecules; c) very small sizes of gas molecules.
- 1. At a constant mass with a decrease in gas volume, its pressure
- b) increases;
- 2. How will the pressure of a gas change if it is heated at a constant volume?
- b) will become more;
- 3. The rubber ball was squeezed by hands and deformed. At the same time, the following changed:
- volume –
- density – pressure –
- 4. The gas in the vessel exerts a pressure of 300 Pa on the left wall. What pressure does the gas produce on the bottom, top and right walls of the vessel?
- V) same in all directions.
- 5. The main reason for gas pressure on the walls of a vessel is
- A) impacts of gas molecules on the walls of a container;
- Pressure transfer
- liquids and gases.
- Pascal's law.
- Pressure produced
- for liquid or gas,
- transmitted to everyone
- directions without
- CHANGES.
- - Blaise Pascal - French mathematician and physicist, one of the minds of the 17th century. Pascal's father, Etienne, an expert in mathematics and astronomy, was involved in his education. Miracle child Blaise began studying science at the age of 12. His father began to take him to meetings of the scientific circle. The boy's intellect developed rapidly and soon he discussed scientific problems on equal terms with major scientists of his time. At the age of 16, he wrote the wonderful “Essay on Conic Sections.” He discovered and studied a number of important properties of liquids and gases, and through interesting experiments proved the existence of atmospheric pressure. A unit of pressure and a popular programming language are named after him. We are still studying the discoveries made by Blaise Pascal 300 years ago.
- Blaise Pascal
- (1623 - 1662)
- The structure of solids, liquids and gases is different!
- Solid particles
- body only
- fluctuate around
- balance, balance
- without moving
- over the body.
- The liquid is fluid,
- and its layers are easy
- shift relative to
- each other.
- Gas particles
- easy and safe
- rearranged
- located throughout the entire volume
- Therefore they differently
- convey the rendered
- there is external pressure on them.
- What's the difference?
- transmit liquids and gases
- influence on them
- external pressure?
- Pascal's law
- Liquids and gases transmit pressure equally in all directions.
- Free mobility
- particles of liquids and gases
- leads to alignment
- total pressure
- DIRECTION!
- PASCAL'S LAW
- Let's stand on one leg
- On the other
- Stand on tiptoes
- reached out
- How has it changed?
- pressure on the floor?
- Well done!
- Sit down.
- The numbers 1, 2 and 3 indicate round holes covered with identical rubber films. When the piston was moved from position A to position B, the films bent outward. In which of the pictures
- One vessel contains a metal cube, the other contains water. How will these bodies transmit the pressure exerted on them?
- In the vessel under the piston there is
- gas. The piston was moved from
- position A to position B
- Did it increase equally with
- this is the gas pressure on the walls
- Vessels at points 1, 2, 3, 4 and 5?
- Think about it
- and about t v e t!
- If you shoot from a small-caliber rifle at a boiled
- egg, a hole is formed. If you shoot at a damp
- the egg will scatter. How to explain this phenomenon?
- Will there be
- toothpaste squeezed out
- tube in conditions of condition
- weightlessness as well as in
- normal conditions?
- Why the explosion
- projectile underwater
- destructive for everyone
- living in water
- organisms?
- Why
- soap bubbles
- acquire
- form
- ball?
- Pressure = Pressure force / bearing area
- p = Fd / S
- Compose the text from fragments A, B, C, D:
- If known...
- A. 1 ... pressure and support area, ...
- 2 ... pressure force and pressure, ...
- 3 ... pressure force and support area, ...
- then you can calculate...
- B. 1 ... pressure ...
- 2 ... pressure force ...
- 3...support area...
- according to the formula:
- B. 1 … Fd / S. 2 … p * S. 3 … Fd / p
- The unit of measurement will be:
- G. 1 ... N. 2 ... m2. 3... Pa.
- Check the answer: A1 B2 C2 D1; A2 B3 C3 D2; A3 B1 C1 D1.
- P*S
- p = Fd / S [P] = [N/m2]=[Pa]
- Compose the text from fragments A, B, C, D.
- A. 1. Pressure in liquids and gases...
- 2. Pressure in solids...
- B. 1. transmitted in the direction of the acting force.
- 2. transmitted equally in all directions.
- Q. 1. This property of solids is due to the fact...
- 2. This property of liquids and gases is due to the fact...
- D. 1. their molecules can move throughout
- directions.
- 2. their molecules only vibrate around the position
- balance.
- ANSWER: A1B2V2G1; А2Б1В1Г2
- 1. The gas pressure on the walls of the vessel and on a body placed in the gas is caused by impacts of gas molecules.
- 2. Gas pressure depends on temperature and on the volume occupied by a given mass of gas.
- 3. Liquids and gases transmit pressure equally in all directions.
- § 35, 36
- Exercise 14
Slide 2
Today in class...
1 Why does gas press? 2 What does gas pressure depend on? 3How does gas transmit pressure?
Slide 3
Repetition
Pa Formula for calculating pressure Pressure units Pascal Blaise 1623 -1662
Slide 4
Which of three identical bars produces more pressure on the table?
Slide 5
New material
Why does the ball increase its volume? Conclusion: The gas pressure on the walls of the liquid and on a body placed in the gas is caused by impacts of gas molecules.
Slide 6
What does gas pressure depend on?
Conclusion: On the temperature of the gas On the volume occupied by the gas.
Slide 7
How do gases and liquids transmit pressure?
Pascal's Law Liquids and gases transmit pressure equally in all directions.
Slide 8
We will answer questions...
The numbers 1, 2 and 3 indicate round holes covered with identical rubber films. When the piston was moved from position A to position B, the films bent outward. In which of the pictures
Slide 9
One vessel contains a metal cube, the other contains water. How will these bodies transmit the pressure exerted on them? The vessel is tightly closed with a stopper into which two tubes are inserted. If you blow into tube a, then water flows out of the vessel through the tube and cube. Will water flow out of tube a if you blow into tube b?
Slide 10
There is gas in the vessel under the piston. The piston was moved from position A to position B. Did the gas pressure on the walls of the Vessel increase equally at points 1, 2, 3, 4 and 5?
Slide 11
If you shoot a boiled egg with a small caliber rifle, a hole will form in it. If you shoot at a damp one, it will fly apart. How to explain this phenomenon? Why is a shell explosion underwater destructive for organisms living in water? Why is a soap bubble shaped like a ball?
In our experiment, moving gas molecules continuously hit the walls of the ball inside and outside. When air is pumped out, the number of molecules in the bell around the ball decreases. But inside the tied ball their number does not change. Therefore, the number of impacts of molecules on the outer walls of the shell becomes less than the number of impacts on the inner walls and the ball inflates until the elastic force of its rubber shell becomes equal to the force of gas pressure. The spherical shape that the inflated shell takes shows that the gas presses on its machines in all directions equally, in other words, the number of molecular impacts per square centimeter of surface area is the same in all directions. The same pressure in all directions is characteristic of a gas and is a consequence of the random movement of a huge number of molecules. So, when the volume of a gas decreases, its pressure increases, and when the volume increases, the pressure decreases.
