What Would Happen If You Did the Old 'Keep a Paper Towel Dry Under Water' Experiment?

Have you ever wondered what would happen if you tried to keep a paper towel dry under water? The short answer is: if the altitude is above a certain point, it will become wet. This intriguing experiment has sparked curiosity and has been the subject of many discussions. Let's delve into the science behind it.

Understanding the Experiment

The experiment typically involves placing a paper towel in a cup and submerging it in water. Under normal circumstances, the paper towel stays dry because the air trapped in the cup maintains a pressure that keeps the water out. However, what happens if the altitude increases significantly?

The Role of Air Pressure

At standard altitudes, the water that enters the cup is primarily due to the pressure difference between the inside of the cup and the outside. The air inside the cup is trapped and maintains a certain pressure. When submerging the cup, this pressure helps keep the water out.

At higher altitudes, the air pressure decreases. This reduction in air pressure means that the pressure inside the cup is less capable of preventing water from entering the cup. As a result, the water level in the cup may gradually rise, eventually coming into contact with the paper towel, causing it to get wet.

Theoretical Experiment at Vacuum

Imagine if you were to perform the experiment in a vacuum. In a vacuum, there is no air, so the pressure inside the cup would be very low. This means that even a small pressure difference from the outside could cause the water to rise inside the cup and potentially wet the paper towel.

However, in reality, we would never reach a complete vacuum, as some air would be trapped in the cup at even the highest altitudes. This trapped air could still provide enough pressure to keep the paper towel relatively dry.

Real-World Considerations

The altitude at which the paper towel might get wet depends on various factors, such as the shape of the cup and the initial amount of air trapped inside. A typical estimate is that this could happen between 8-12 km up, depending on the specific conditions.

Conclusion

The experiment of keeping a paper towel dry under water becomes fascinating when we consider the role of air pressure at different altitudes. While it may seem counterintuitive, the decrease in air pressure at high altitudes can lead to the paper towel getting wet. This experiment not only demonstrates the principles of air pressure but also highlights the importance of understanding atmospheric conditions in various scenarios.