Cooling is produced when a gas at high pressure suddenly expands. Why?

Explanation

### Step-by-Step Solution:

1. **Understanding Gas Expansion**: When a gas at high pressure expands suddenly, it does work on the surroundings. This process is known as expansion work.

2. **Work Done by the Gas**: During the expansion, the gas exerts a force over a distance to push against the external pressure. This work done is a form of energy transfer from the gas to its surroundings.

3. **Internal Energy and Temperature**: The internal energy of a gas is related to the kinetic energy of its molecules. When the gas does work, it loses some of its internal energy.

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