The phenomenon of bubbles forming and rising when you tilt the open mouth of an empty bottle submerged in water is a result of the change in pressure inside the bottle as you change its orientation. Here's an explanation of this phenomenon:
1. **Initial Equilibrium**: When the bottle is initially submerged in the water with its mouth facing downward, the air pressure inside the bottle is equal to the external water pressure. There is no significant difference in pressure, so no bubbles are formed.
2. **Tilting the Bottle**: When you start to tilt the bottle with the mouth facing upwards, the orientation of the bottle changes, but the air inside the bottle tends to remain at the same pressure as before due to its inertia. As a result, the pressure inside the bottle decreases relative to the increasing external water pressure as you move deeper into the water.
3. **Pressure Difference**: The pressure difference between the air inside the bottle and the water outside becomes significant. This pressure difference causes the air inside the bottle to expand, creating a lower pressure zone inside.
4. **Bubble Formation**: To equalize the pressure inside and outside the bottle, air from inside the bottle begins to escape through the mouth. As the air escapes, it rises to the surface of the water, forming bubbles.
5. **Continuous Process**: The process continues as long as the bottle is tilted and air is allowed to escape through the mouth. Once the bottle is oriented vertically again, the pressure inside the bottle and outside it equalize, and bubble formation stops.
In summary, the formation of bubbles when you tilt the open mouth of an empty bottle in a bucket of water is a result of the pressure difference between the air inside the bottle and the water outside it as the bottle's orientation changes. This difference in pressure causes air to escape through the mouth, forming bubbles that rise to the water's surface.