Air Pressure Breaks a Ruler

Materials: ★☆☆ Easy to get from supermarket or hardware store
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★★☆ Some safety precautions required to perform safely

Categories: Pressure and Fluids, The Atmosphere, Science Shows

Alternative titles: The Heavy Newspaper

Summary

A ruler placed on the edge of a table with covered by a piece of paper can be broken by a swift strike.

Procedure

Place a wooden ruler so that about 5 inches extend beyond the edge of a sturdy table.
Strike the overhanging end sharply with the side of your hand and observe the result.
Reset the ruler in the same position on the table.
Spread a sheet of paper flat across the portion of the ruler on the table, smoothing out air pockets.
Strike the overhanging end of the ruler in the same way as before.
Observe that the ruler is much harder to move and may snap from the force of your strike.

Links

Air Pressure Breaks a Ruler - George Mehler:

📄 Break a Ruler Using Newspaper and Atmospheric Pressure - Education.com: https://www.education.com/activity/article/pressure-news-pretty-heavy/

Variations

Try using different sizes of newspaper sheets to see how surface area affects the result.
Try gently lifting the ruler with the paper covering it - notice the suction effect.

Safety Precautions

Strike with the soft part of your hand to avoid injury.
Use only thin, inexpensive wooden rulers (not metal-edged rulers, which may cause injury).
Clear the area of breakable objects, as rulers may snap and fly off the table.
Adult supervision recommended for children performing this demonstration.

Questions to Consider

Why is it harder to break the ruler when covered with newspaper?
How does atmospheric pressure contribute to the effect?
Why is smoothing the newspaper important?
How does this relate to the concept of suction cups?
How much force do you think the atmosphere exerts per square inch on the paper?