The image shows two scenarios involving a glass of water and a flat surface (possibly a piece of cardboard or paper), illustrating the concept of
atmospheric pressure and how it can support a liquid in an inverted container.
Let's analyze both diagrams:
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🔹 Left Diagram:
- A hand holds a glass filled with water.
- A flat sheet (e.g., cardboard) is placed on top of the glass.
- The arrows pointing
downward suggest that the person is pressing down on the sheet to keep it in place.
- This setup is
before the glass is flipped.
👉 This represents the
initial state, where the sheet is being held in place by the person’s hand, preventing the water from spilling out.
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🔹 Right Diagram:
- The glass is now
inverted, upside-down.
- The same flat sheet is still covering the opening.
- The hand is holding the glass from the bottom (now at the top).
- Arrows pointing
upward indicate
atmospheric pressure acting on the underside of the sheet.
- The water does
not spill out, even though the glass is upside-down.
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✔ Explanation:
This is a classic demonstration of
atmospheric pressure.
#### Why doesn't the water fall out?
1. When the glass is full of water and covered with a flat sheet, and then carefully turned upside down:
- The water tends to flow out due to gravity.
- However, the
air pressure from the atmosphere pushes upward on the sheet from below.
- This atmospheric pressure is about
101,325 Pascals (Pa) at sea level — enough to support a column of water about
10 meters high.
2. The
weight of the water in the glass is much less than what atmospheric pressure can support.
- So, the upward force from air pressure
balances the downward force of the water’s weight.
- As long as the seal between the sheet and the glass is intact (no air enters), the water stays inside.
3. The sheet is also slightly pushed into the rim of the glass due to the pressure difference, helping maintain the seal.
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🧠 Key Concept: Atmospheric Pressure
- Air exerts pressure in all directions.
- In this experiment, atmospheric pressure
pushes up on the card, counteracting the
downward pull of gravity on the water.
- This demonstrates that
air has weight and exerts pressure.
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🚫 What happens if you remove your hand?
If you slowly release your hand after inverting the glass:
- The water will stay in place
as long as the seal is maintained.
- If air gets under the card (e.g., due to a small gap), the pressure equalizes, and the water spills out.
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✔ Conclusion:
This is a simple but effective demonstration that
atmospheric pressure is strong enough to support the weight of water in an inverted glass, provided there's no air entering from below.
> 💡
Fun Fact: This trick works best with a tall glass because the pressure difference needed to hold the water increases with height — but for typical glasses, atmospheric pressure easily supports the water.
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Let me know if you'd like to simulate this or see variations!
Parent Tip: Review the logic above to help your child master the concept of 6th grade science activity.
