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# Measuring atmospheric pressure with a barometer

The atmospheric pressure is the pressure due to the air in the atmosphere. Atmospheric pressure can be measured with a barometer.

A barometer is made by filling a tube with mercury and then placing the tube upside down insde a bath of mercury.

The atmosphere pushes against the mercury bath which pushes the mercury up the tube. The space between the top of the column of mercury and the top of the tube is a vacuum.

The vertical height of the mercury column gives the atmospheric pressure: \begin{align*}\Tred{\text{atmospheric pressure}} = & \text{density of mercury} \times \Tblue{\text{height of column}} \\& \times \Tgreen{\text{gravitational field strength}} \end{align*}

Note that the width of the tube does not matter in this calculation.

A barometer is used to measure the pressure of the atmosphere.