### Atmospheric pressure - Upside down glasses of water

Above us there is at least several kilometers thick air layer, which acts on the force of gravity -> rise in the air, "atmospheric" pressure.

Normal atmospheric pressure is 101325 Pa value. This value is surprisingly high, following an attempt to prove that pressure really has.

**Educational phase:** motivation, application

#### Required aids

- paper / cardboard
- a glass with straight neck
- colored water
- cloth

#### Experiment schema

#### Experiment instructions

Fill the jar to the brim with water. | |

Lay paper and slightly press. | |

Turn the glass upside down. | |

Non-waste paper from the jar, the water stays inside the glass does not flow. |

#### Explanation

The paper has the force due to pressure from below atmospheric pressure, which is larger (the paper is slightly bent in a glass) than the hydrostatic force inside the glass, caused by gravitational force acting on the water.

#### Physical interpretation

The paper falls off and water poured out only when the hydrostatic pressure inside the jar will be greater than the atmospheric pressure around it. This does not depend on the volume of water, but the height of the water column, ie height glass. We assumed Torricelli experiment, so we use the principle of connected vessels, where atmospheric pressure is in equilibrium with hydrostatic. After putting numerical find that the maximum height of water column (glass) in the case of water about 10 meters.

{p_{a}} = 101325 Pa

{\varrho_{H_{2}O}} = 998 kg \cdot m^{-3}

\underline{g = 9,81 m \cdot s^{-3}}

{p_{a}} = h \cdot {\varrho_{H_{2}O}} \cdot g

h = \frac{p_{a}}{h \cdot {\varrho_{H_{2}O}} \cdot g} = \frac{101325}{9.81 \cdot 998} = \underline{10,34m}

#### Application in practice

Well, capillary phenomena.

#### Note

An attempt to perform over a sink or lavoro.

#### Control issues and challenges

- The original experiment was carried out with mercury. How high was a column of mercury?