Robert Boyle was experimenting with the air pump with the help of Robert Hooke. Hooke designed the pump and Boyle used it to discover a whole series of important facts. He showed that sound didn't travel in vacuum, proved that flame required air and he investigated the elastic properties of air.
A real world example would be the popping of your ears at a high altitude. It is due to the unbalanced pressure of the air outside and inside of our ears.