Question

which statements correctly describe the properties of air? select three options. air has mass but no weight. air pressure is created by the weight of the atmosphere pushing on earth’s surface. pressure is a measure of how tightly molecules are packed. denser air is heavier than less dense air. air is less dense at higher altitudes.

Explanation:

• Air pressure is created by the weight of the atmosphere pushing on Earth's surface: Air has mass, and due to gravity, this mass exerts a force (weight). The cumulative weight of the air column (atmosphere) above a surface creates air pressure.
• Denser air is heavier than less dense air: Density ($

ho=\frac{m}{V}$) is mass per unit volume. If two volumes of air are considered, for a given volume $V$, a higher - density ($
ho$) air has a higher mass ($m =
ho V$). Since weight $W=mg$ (where $g$ is the acceleration due to gravity), denser air (with more mass) is heavier.

• Air is less dense at higher altitudes: As altitude increases, the number of air molecules per unit volume decreases. Using the density formula $

ho=\frac{m}{V}$, with fewer molecules (less mass $m$) in the same or larger volume (as air can expand), the density $
ho$ of air decreases.

• Air has mass but no weight: This is incorrect. Weight $W = mg$ (where $m$ is mass and $g$ is the acceleration due to gravity). Since air has mass ($m>0$) and $g>0$ on Earth, air has weight.
• Pressure is a measure of how tightly molecules are packed: This is a description of density ($

ho=\frac{m}{V}$), not pressure. Pressure is force per unit area ($P = \frac{F}{A}$).

Answer:

• Air pressure is created by the weight of the atmosphere pushing on Earth's surface.
• Denser air is heavier than less dense air.
• Air is less dense at higher altitudes.