Boyle's Law states that when the temperature is kept constant, the relationship between volume and pressure is inversely proportional. As the volume decreases, the pressure increases, meaning as the one doubles, the other halves. This law aided in the invention of syringes and explains the science behind balloons, plane travel and bubbles.
Boyle's Law is important when using a syringe. When fully depressed, the syringe is at a neutral state with no air in the cylinder. When the plunger is pulled back, you are increasing the volume in the container and thus reducing the pressure. They are inversely proportional and one must decrease while the other increases. The liquid draws up into the syringe because it balances the pressure, making it equal to the pressure outside of the syringe.
Popping a Balloon
When popping a balloon, you are attempting to reduce the amount of air trapped inside of the container, thus, you increase the pressure on the system. You squeeze the balloon, increasing the pressure, which decreases the volume. The system will become too disproportional, too stressed, and must pop to equalize the system. The same happens when you overfill a balloon, putting too much pressure proportional to the volume the container can handle.
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When ascending or descending in a plane, or taking a subway or train under a deep waterway, your ears "pop," or feel uncomfortable because of a change of pressure in your head. Our ears maintain a level of water that helps you stay balanced and adjust to altitude changes. When this happens quickly, like during a plane's take-off, the pressure in your ears builds along with an increased volume. This goes against Boyle's Law. You must swallow hard to release some of the pressure through an opening in your throat that creates an equal system outside and inside your ear.
Boyle's Law is extremely helpful for SCUBA divers. As you dive deeper, the pressure increases on your body and decreases the volume in your lungs. As you ascend out of the depths of the ocean, you slowly release air from your lungs, which is compressed due to the pressure. Divers are taught to exhale steadily as they rise to the surface, because air in their lungs compressed as they submerged and is expanding as they rise. Failing to expel the expanding air could lead to severe internal injuries.