Wind, Pressure, and Density

Vocabulary flashcards covering pressure, atmospheric pressure, density, barometers, wind dynamics, and Bernoulli's principle from the lecture notes.

Pressure

The perpendicular force acting per unit area ($P = \frac{F_{\perp}}{A}$).

Pascal ($\text{Pa}$)

The SI unit of pressure, defined as one newton per square metre ($1\,\text{Pa} = 1\,\text{N/m}^2$).

Atmospheric Pressure

The pressure exerted by the weight of atmospheric gases, denoted by $P_{\text{atm}}$.

Normal Atmospheric Pressure

Standard atmospheric pressure equal to $101325\,\text{Pa}$ ($\approx 10^5\,\text{Pa}$), $1\,\text{bar}$, $1\,\text{atm}$, or $76\,\text{cm}$ ($760\,\text{mm}$) of $\text{Hg}$.

Bar

A unit of pressure equal to $10^5\,\text{Pa}$.

Barometer

An instrument in which a mercury column stays at $76\,\text{cm}$ ($760\,\text{mm}$) under normal atmospheric pressure.

Mercury Level Variation in a Barometer

The mercury column in the test tube falls below $76\,\text{cm}$ if atmospheric pressure decreases, and rises above $76\,\text{cm}$ if atmospheric pressure increases.

Atmospheric Pressure and Altitude

Atmospheric pressure decreases with altitude because atmospheric gases decrease and the weight of the air above decreases with height.

Area and Pressure Relationship

For a given applied force, a lesser area results in more pressure ($P = \frac{F}{A}$).

Density

Mass per unit volume ($1\,\text{cm}^3$ or $1\,\text{m}^3$), denoted by the Greek letter Rho ($\rho$) and calculated as $\rho = \frac{m}{V}$.

SI Unit of Density

Kilograms per cubic metre ($\text{kg/m}^3$).

CGS Unit of Density

Grams per cubic centimetre ($\text{g/cm}^3$).

Wind

The movement or flow of air from a high pressure region to a low pressure region.

Temperature Effect on Air Density

When temperature increases, the density of air decreases, meaning hot air is lighter than cold air.

Wind Current

Air flow caused when lighter, heated air rises and cooler air from the surroundings flows in to take its place.

Bernouli's Principle

The principle stating that if wind (air) speed is high at a point, atmospheric pressure is low, and if wind speed is low, atmospheric pressure is high.

Sea Breeze

A breeze that takes place during the day due to temperature and pressure differences between land and sea.

Land Breeze

A breeze that takes place during the night due to temperature and pressure differences between land and sea.