Simple science experiment

Today I am writing about a simple science experiment. For this, no parental guidance is required ! Take water in a glass. Now put a straw inside the glass. Hold a straw outside the glass in hand. Now put both the straws in the mouth and try to suck water. WE CANNOT !!!! Though one straw is inside the glass and touching the water level, still we can't suck the water from either of straws. WHY ???.. Air is lighter than water. In scientific terms, density of air is less than that of water. So when we are trying to suck water, one straw in water and another in air, air being lighter than water, is easily sucked first inside the mouth through straw. Now our mouth is not empty. It is full of air. This air puts pressure on the entry of water. In other words, the space is already occupied by air and this air is not allowing the water to come inside. That's why we cannot suck water.