What are the uses of pressure

Pressure - measurement and application

Introduction and physical basics

The print is a physical one State variable. It describes the relationship between the amount of a force $ \ vec {F} $ and the area $ A $ on which it acts. The symbol for printing is a small $ p $ (from the English "pressure "), not to be confused with the large $ P $, the formula symbol for performance.

$ p = \ frac {\ vert \ vec {F} \ vert} {A} $

The unit of pressure is the pascal ($ \ text {Pa} $). It describes the force effect of one Newton on one square meter ($ 1 ~ \ frac {\ text {N}} {\ text {m} ^ 2} $). Another unit for pressure is $ \ text {bar} $. $ 100,000 ~ \ text {Pa} $ correspond to one $ \ text {bar} $.

As the volume or the temperature the pressure characterizes the state of a physical system. Such not directional Sizes will be scalar Called sizes. Vectorial In addition to the amount, sizes always have a direction in which they point. An example is the force $ \ vec {F} $.

Example air pressure

The air pressure at sea level is approximately $ 1 ~ \ text {bar} $. So there is a force of $ 100,000 ~ \ text {N} $ on every square meter of the earth's surface. That sounds like a lot, but our bodies have always been adapted to this pressure so that we do not notice anything. In a closed system, for example in a car tire, the air pressure is the same everywhere.

Example gravity pressure

You have probably noticed that you feel pressure on your ears when you dive deep into the water. The reason is that the water exerts a weight on your eardrum due to its mass. So there is also pressure under water, one speaks of Gravity pressure. The formula for the gravitational pressure is:

$ p = \ rho g h $.

Here $ \ rho = \ frac {m} {V} $ is the density, $ g $ is the acceleration due to gravity and $ h $ is the height of the water column above you.

The particle model

The Particle model is used to get an idea of ​​what pressure actually is. An inflated balloon is to be considered as an example: In the particle model, the smallest building blocks of the air are called Bullets described, which is in the balloon move freely can. They bump into each other or hit the wall of the balloon. There is a Impulse transfer or a force from the particles on the wall instead. The ratio of the total force applied and the surface area of ​​the balloon is the pressure.

The pressure in trapped gases, as in the balloon, also depends on the temperature from. The temperature of a gas is that medium kinetic energy of the particles. If the temperature increases, the particles also become faster and collide more frequently. As a result, the pressure increases. Instead, do you decrease the Amount of gasBy letting air out, the pressure also decreases as there are fewer particles to collide with. It is the same volume crucial. If you squeeze the balloon, you reduce its volume. You can feel the pressure rise until the balloon bursts.

manometer

A manometer is a measuring device for measuring pressure. If it is used specifically for measuring air pressure, it is known as barometer. A Can barometer deforms depending on external pressure. The bulging of the can is transferred to a pointer that shows the air pressure on a scale. Another form of the barometer is that Liquid barometer. This is a curved tube that is open on one side and airtight on the other. The liquid changes its fill level depending on the air pressure.

Precise knowledge of the air pressure is used by aircraft to determine the flight altitude. In meteorology it is needed for weather forecasting.

Hydraulics

The fact that the pressure in a system is the same everywhere is reflected in the Hydraulics as Force converter used. This makes it possible to lift a car that weighs tons with mere muscle power. All you need is a Jack. The muscle power is transferred to a relatively small area via one lever. This creates the same pressure everywhere in the hydraulic line. On the other side of the jack, the pressure acts on a much larger area, which also increases the force in the same way. If the ratio of the areas is chosen correctly, your own muscle strength can be increased so much that it is sufficient to lift a car.