Pascal's law for liquids and gases says that pressure, propagating in a substance, does not change its strength and is transmitted in all directions equally. Liquid and gaseous substances behave under pressure with some differences. The difference is due to the behavior of particles and the weight of gases and liquids. In the article, we will consider all this in detail with the help of visual experiments.
Is fluid pressure transmitted
Let's take a cylindrical vessel, which is hermetically sealed from above by a piston. There is a liquid inside, and a weight is on the piston. It exerts pressure with a force equal to its weight. This pressure is transferred to the fluid. Its molecules, unlike particles of a solid body, can freely move relative to each other. There is no strict order in their arrangement, they are scattered randomly.
Knowledge of featuresthe motion of particles of different substances in the future will help us understand Pascal's law for liquids and gases. How will the liquid molecules behave if we act on them with the pressure force of the weight? Experience will help us answer this question.
How fluid behaves under pressure
The model of the liquid will be glass beads, and the model of the vessel will be a box without a lid. Balls, as well as particles of a liquid substance, move freely in containers. Take any item that is the same width as the width of the box. It will imitate a piston.
Push the piston on the liquid. How do its molecules behave? We see that they press both on the bottom of the container and on its walls. They push each other and try to fall out of the box. If it were a real liquid, then it would tend to splash out of the vessel. Later, when studying Pascal's law for liquids and gases, we will see this in practice. Due to the fact that the molecules move freely, the pressure exerted by the weight is transmitted both to the sides and down. And what happens if you replace liquid with gas?
How air behaves under pressure
Let's say we have a cylinder with a piston filled with air. Place a weight on top of the piston. How is the pressure applied to the gas transferred? As the piston moves down, the distance between the molecules at the top of the gas decreases, but not for long. The speed of gas molecules is hundreds of meters per second. The distance between them is much greater than their size. They move in random directions and collide with each other.
When the pistonfalls, the particles are simply locked in a smaller volume. As a result, they more often hit the walls of the vessel, and as the volume of the gas decreases, its pressure increases. This postulate must be remembered, so that later it would be easier to understand Pascal's law for liquids and gases. The number of beats per second per square centimeter is almost the same. This means that the pressure that the piston produces is transmitted in all directions without change.
Pressure transfer in different directions
Pascal's law, the transfer of pressure by liquids and gases cannot be understood if one does not understand one oddity: how is it that we press down, and the pressure is transferred both down and to the sides? But what if a tube is attached to the cylinder, will the pressure be transmitted upward through it? Let's experiment.
Take two syringes filled with water and connect them with a tube. Let's observe how the pressure will be transmitted by the liquid that is in the syringes. Press on the plunger of one syringe. The force of pressure on the piston, and hence on the liquid, is directed downward. However, we see that the piston of the second syringe rises. It turns out that the pressure, transmitted through the tube, changes the direction of the force. Interestingly, syringes can be placed not only vertically, but also at right angles to each other. The result will be the same.
Pour out the water, and there will be air in the syringes. Let's repeat the experience. In the course of the experiment, we will see that the gas also transmits pressure in all directions. There is only one difference with liquid. If you lower the piston of onesyringe down and fix it with your finger, then when you press the piston of another syringe, the gas will compress. Its volume will decrease by about two times, and the piston will strive to bounce up. This gas, seeking to increase its volume, causes the piston to move upward. It would be different with a liquid, it would not be possible to compress it so easily.
Pascal's law
We will study the transfer of pressure by liquids and gases with the help of experience. It was invented by the French physicist Blaise Pascal. Take a hollow sphere to which a glass tube is attached. In different parts of the ball (top, side, bottom) there are small holes. A piston is placed inside the tube. This is a special device for demonstrating Pascal's law.
Fill the balloon through the tube with water to see how it behaves. Although gravity acts on the ball from top to bottom, trickles of water flow out of the holes of the ball at an angle, to the side, and even up. Of course, they deviate slightly from their original direction, because gravity acts on them. We see that the pressure exerted on the water is transmitted in all directions.
If instead of water we take smoke and do this experiment, we will observe the transfer of pressure in a gas with our own eyes, because smoke is a gas colored with small particles of soot or tar. Due to the fact that it is very light, it will not be affected by gravity as much, it will not deviate from its original position as much as streams of water. We can conclude this: the pressure exertedon a liquid or gas, is transmitted, without changing the force, to any point of the liquid and gas in all directions. This is Pascal's law for liquids and gases. Formula: P=F/S where P is the pressure. It is equal to the ratio of the force F to the area S, on which it acts perpendicularly.
