When a empty glass is kept close to ear why you hear sound?

When a seashell is free of its inhabitant, it is simply an empty chamber. Because of this, it is able to amplify and distort the sound of air traveling across its surface in a way filled vessels cannot. The sound that comes from the inside of a shell is the sound of air moving across and within the shell. The cavity of the seashell allows the noise to echo and resonate. The movement of air is constant, so the noise coming from the interior of the shell is a continuous whooshing, which is very similar to the sound of the ocean