Week 37
Pressure Inside and Outside
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.
Students use their own faces as a direct experience of inside and outside pressure, observing what happens when they increase pressure inside the mouth and when they decrease it, then connecting each observation to the pressure rule.
Students create a partial vacuum inside a plastic bottle and observe how outside air pressure responds, making the abstract concept of pressure difference physically visible.
- 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.
- 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.
- 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?
Students use their own faces as a direct experience of inside and outside pressure, observing what happens when they increase pressure inside the mouth and when they decrease it, then connecting each observation to the pressure rule.
- With your mouth relaxed and slightly open, press your cheeks gently. They move easily. This is equal pressure on both sides.
- Close your mouth and puff your cheeks out as far as you can. Now press your cheeks. What is resisting your fingers? What has increased inside your mouth?
- Suck your cheeks in as far as you can. Who pushed them in? Was it a pulling force from inside, or a pushing force from outside?
- Put a straw in a glass of water. Take a sip while thinking: what is actually moving the liquid? Stop partway and think through the pressure on the water surface outside the straw versus inside your mouth.
- Take a slow deep breath with your hand on your chest. Feel your chest expand. What does that expansion do to inside pressure? What does outside air then do?
- In your notebook, write out the sequence for how a straw works in three steps, using only the words pressure, higher, lower, push, and flow.
Students create a partial vacuum inside a plastic bottle and observe how outside air pressure responds, making the abstract concept of pressure difference physically visible.
- One empty plastic water bottle with a cap
- A notebook and pencil
- Squeeze the bottle firmly to push some air out, then quickly put the cap on while still squeezing.
- Release the squeeze while keeping the cap on. Watch what happens to the shape of the bottle.
- Describe in your notebook: what happened, and why? What is different inside the bottle versus outside right now?
- Open the cap slowly. Listen and describe what you hear. Which direction is air flowing, and why?
- Repeat with one full breath of air blown into the bottle before capping. Now which direction does the bottle bulge when you release? What changed?
L37_Pressure_Inside_and_Outside by Selene