Education Technology

## Summer of STEM: Breaking Board Paradox

Posted 06/21/2018 by Erick Archer

Put a paint stick on the edge of a table with a little less than half the length hanging off the table‘s edge. Now, karate chop it. Did it break? Of course not. It just flew off the table, still intact. Now, do the same set up – this time laying a large piece of newspaper across the part of the stick that is still on the table. Karate chop the part of the stick that is hanging off the table, and voila! The stick breaks! But why?

What you’ll need:
• A few paint sticks from a local hardware store.
• An unfolded piece of newspaper about 3’ x 3’ in area. Butcher paper or thicker wrapping paper will also work.
• A table, a glove to avoid splinters, and goggles to protect your eyes.
What to do:
• Lay the paint stick on the table so that about half is hanging off the table.
• Ensuring no one is in the path of the flying stick, karate chop the part of the stick that is hanging off the table.
• The stick should fly across the room but should not break.
• Now, do the same set up – but this time, lay the paper across the edge of the stick that is still laying across the table.
• With a fast-moving karate chop, try to break the edge of the stick that is hanging off the table. (Be sure you do not mistakenly hit your hand on the table!)
• The stick will likely break.
How it works:
• The paper, by itself, weighs very little. You can try another variation to prove this by crumpling the paper into a ball and setting it on the part of the stick that is still on the table.
• Karate chop it and notice the stick doesn’t break.
• When the paper is placed completely flat on top of the stick, it serves as a large surface area for the air above it to push down on the paper – and by extension, onto the stick.
• A 3’ x 3’ piece of paper across the stick is equivalent to roughly 19,000 pounds of pressure.

Below, see a video of this experiment and others in action: