Explain why water does not run out of a dropper unless its rubber bulb is pressed.

(N/A) The dropper works based on the principle of atmospheric pressure. When the rubber bulb is not pressed,the air pressure inside the dropper is equal to the atmospheric pressure outside. Since there is no pressure difference,the water remains inside due to surface tension and the balance of forces. When the rubber bulb is pressed,the volume of air inside decreases,which increases the air pressure inside the dropper. This increased pressure pushes the water out of the nozzle.