Learners investigate what happens when the air pressure on one side of a surface differs from the pressure on the other side. Students build on their understanding of air pressure to discover that equal pressure produces no sensation at all, while unequal pressure produces a push toward the lower-pressure side. The central insight of the lesson is that nothing in nature ever pulls air. Whenever air moves into a space, it is being pushed by higher-pressure air from outside. Students apply this principle to straws, breathing, ear popping, and the behavior of flexible containers, discovering that the same rule explains all of them.

Workbook Pages 

Key Ideas

• When pressure is equal on both sides of a surface, you feel nothing. The forces balance exactly.
• When pressure is unequal, the higher-pressure side pushes toward the lower-pressure side. The bigger the difference, the harder the push.
• Nothing in nature pulls air. When air moves into a space, it is always being pushed by higher pressure elsewhere.
• A straw works because reducing pressure inside your mouth lets the atmosphere push liquid up from below. You do not pull the liquid.
• Breathing follows the same rule. Inhaling expands the chest, lowering inside pressure, and the atmosphere pushes air in. You do not pull air in.
• Ears pop because pressure inside the ear must equalize with outside pressure through a narrow tube. The pop is air squeezing through in small bursts.

Vocabulary

• Inside Pressure: The pressure of air or gas inside a container, space, or body cavity.
• Outside Pressure: The pressure of the air surrounding the outside of a container or surface.
• Atmospheric Pressure: The pressure created by the weight of the entire atmosphere pressing down on Earth’s surface. About 14.7 psi at sea level.
• Unequal Pressure: When pressure is different on two sides of a surface. The higher-pressure side pushes toward the lower-pressure side.
• Eustachian Tube: The narrow tube connecting the inner ear to the throat. Air travels through it to equalize ear pressure.

Discussion Questions

• When you puff your cheeks out, what has changed about the air pressure inside your mouth compared to outside? What is doing the pushing?
• If you poked a small hole in the top of a juice box, why would the liquid stop flowing freely through the straw?
• Why does going down a hill or descending in an airplane often feel worse on the ears than going up?