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  1. Without watching the video, it is called nucleation. Small imperfections in the surface allow for bubbles to form easily. As the bubbles form it is easier for more and more to coalesce in the same spot.

  2. Nice answer here already. To expand a bit further, we can compare a similar phenomenon to fluids on a larger scale where we can see all the action. You might imagine water flowing along the mostly flat ceiling of a cave. Why doesn’t the water just fall down under gravity? Adhesion, attractive molecular forces between different materials, tries to hold the water to the surface seeming to defy gravity. These two opposing forces aren’t usually lined up so perfectly as to cancel each other out. The surface is never perfectly parallel to gravity so the water flows along the surface toward the lowest point. There it might hit a stalactite, pool at the bottom, and eventually gather enough mass of extra water that the pull of gravity overcomes the adhesive forces. Then a water drop falls.

    Gasses dissolved in liquid behave similarly except the buoyant force would play the role of gravity in our earlier example, pulling the material upward. The bubbles you see are a collection of enough separate gas molecules collecting at a single point to finally overcome adhesion and rise to the surface. For a well manufactured glass, these slight imperfections in the surface might be imperceptible to the human eye.

    Ninja edit: Spelling and clarifications.

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