# Effect of gravity on atmosphere

• jackrabbit
In summary, the Earth's gravity does pull the atmosphere down towards the surface, but the air is able to push back up and reach a point of equilibrium. This is due to the Earth's round shape, which allows the air to "meet at the other end" and hold itself up. The density of air is also greater at the surface, which contributes to this equilibrium. Additionally, the movement and temperature of air molecules play a role in this process, as warm air rises and cold air falls, creating a cycle of movement in the atmosphere.
jackrabbit
My ten year old asked the following question - why doesn't gravity pull the atmosphere all the way down to the surface of the earth?

Have you ever used an air mattress? Your laying down on an air mattress compresses the gas in the mattress somewhat, just enough to support your weight. No part of your body is touching the ground if the mattress is sufficiently inflated. Similarly, gravity does pull the atmosphere down toward the surface of the Earth, just enough to support the weight of all of the air above it.

That atmospheric pressure at sea level is 1 atmosphere or 101.325 kilopascal can be used to estimate the weight and thus the mass of the atmosphere. The Earth's equatorial radius is 6378.1 km while its polar radius is 6356.8 km. Using
• The average of these two numbers, 6367.4 km, as an estimate of the Earth's mean radius
• The standard formula for the surface area of a sphere, $A=4\pi r^2$
• The mean gravitational acceleration at sea level is g=9.80665 m/s2

$$W_{\text{atmos}} \approx \frac{4\pi\,(6367.4\,\text{km})^2\cdot 101.325\,\text{kPa}} {9.80665\,\text{m}/\text{s}^2} = 5.26\cdot 10^{18}\,\text{kg}$$

This is a simple yet fairly accurate estimate of the total mass of the atmosphere.

I like to think of it like this: Gravity pulls the air down, but the air pushes back up! And so the two reach a point of equilibrium.

Well the answer is It Does.

The Earth gravity does pull the atmosphere down to the surface, and holds it.

If the Earth was flat, all the air would indeed fall and spread all over. But since it is round, air "meets at the other end" and holds itself up.

The density of air is greater at the surface. It is "squashed up" by the air above.

Air molecules move at extremely high speeds which allow them to temporarily move away from the ground. As they move up some of the kinetic energy (i.e., heat) is lost causing them to slow down, but they are also farther from the center of the Earth so the gravitational attraction is lower allowing them to stay up longer. the push of warmed air from the ground helps hold up the colder air until a downdraft allows the cold air to fall. When cold air falls it can create a vacuum which draws up warmed air. In extreme cases this process helps produce tornadoes.

## 1. How does gravity affect the atmosphere?

Gravity plays a crucial role in keeping the atmosphere close to the Earth's surface. Without gravity, the atmosphere would escape into space, making our planet inhospitable for life.

## 2. Does gravity affect the density of the atmosphere?

Yes, gravity affects the density of the atmosphere. As you move closer to the Earth's surface, the force of gravity increases, causing the air molecules to be packed closer together, resulting in higher air density.

## 3. How does gravity contribute to atmospheric pressure?

Gravity creates pressure by pulling the air molecules towards the Earth's surface. This pressure is responsible for keeping the atmosphere in place and also affects weather patterns and air movement.

## 4. Can gravity affect the composition of the atmosphere?

Gravity plays a significant role in determining the composition of the atmosphere. It helps to keep the lighter gases, such as oxygen and nitrogen, close to the surface, while heavier gases, such as carbon dioxide, tend to rise to the upper atmosphere.

## 5. How does gravity affect the temperature of the atmosphere?

Gravity has a minimal direct effect on the temperature of the atmosphere. However, it indirectly affects temperature by causing atmospheric pressure, which influences the movement of air and the distribution of heat throughout the atmosphere.

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