How do bubbles form when you blow from the straw into the cup?
You are forcing air from your lungs into the water through the straw. Even if you provide a continuous and steady supply of air, you will see that you will not get a huge air bubble but instead you will get many small air bubbles. How does this happen? As air reaches the bottom of the straw and starts coming out of it will immediately experience buoyancy, which pushes the air upwards. This can be explained by Archimedes’s Principle but this is not your question so let’s don’t spend time here. Water is surrounding the air as it peeks through the bottom end of the straw. The surface tension in the interface water-air keeps (to some degree) the air mass together as the bubble forms in the opening of the straw. There will be a time where the buoyancy experienced by the mass of air being pumped is greater than the surface tension trying to keep this volume of air together and at this time the air mass will split and break: one part will move upwards and the other part will still remain in t
