Here's why:

* Pressure and Particle Density: Pressure in a gas is directly related to the density of particles. High pressure means a higher concentration of particles in a given volume.

* Random Motion: Gas particles are in constant random motion. They collide with each other and with the walls of their container.

* From High Concentration to Low: When there is a difference in particle concentration (and therefore pressure), particles naturally move from areas of high concentration (high pressure) to areas of low concentration (low pressure) to try and even out the distribution.

Think of it like this: Imagine you have a room full of people and then open a door to an empty room next door. People will naturally move from the crowded room (high pressure) into the empty room (low pressure) until the density is more even.

Diffusion is a fundamental process in many physical and biological systems. It plays a role in:

* Gas exchange in the lungs: Oxygen diffuses from the alveoli (air sacs) into the blood, and carbon dioxide diffuses from the blood into the alveoli.

* The movement of nutrients and waste products in cells.

* The spread of scents and odors.

Let me know if you'd like more details about any of these examples!