Sometimes you do a cool science trick and everyone nods and smiles and tells you that’s pretty interesting and other times you do a cool science trick and your friends look at you like you’re a bad-ass magic-slinging wizard of the white council. This is one of those times. In this edition of Science! For Parties! I teach you the secrets of (drum roll please) The Cowardly Pepper!
For this trick you’ll need some simple household items: pepper (or any kind of visible seasoning); dish soap; a bowl or plate (if you use a plate try to use a large one with a bit of depth to it); and water. Fill up your bowl with water then cover the water in pepper (the more you use the cooler the effect). Put a dab of dish soap on the end of your finger and dip it into the center of the bowl. The pepper will run away! If you really want to be tricky ask one of your friends to put their finger in first then when nothing happens you can use your secretly dipped in dish soap finger to make your friends think that you’re made of magic.
If you’re uncomfortable with your friends believing that you’re a wizard you can explain the trick to them. It relies on the scientific property of surface tension. Surface tension is what we call that elastic like membrane formed by the liquid molecules’ tendency to have a greater attraction to each other than to the air molecules surrounding them. In this case the pepper rests on the top of the water because it does not exert enough force to break through the surface tension of the water. But when you add the dish soap to the equation it lowers the surface tension of the water by introducing a liquid with weaker molecular attraction than water. This is when the pepper runs for cover.
The thing is it’s not actually the pepper that’s making a break for it but the water the pepper is floating on. You see with its surface tension lowered at the point your finger enters the water the water molecules are repelled by the disruption and attracted to the stronger cohesive forces at the edges of the bowl. So the water runs away and the pepper is just along for the ride. Cool right?
That’s it for this edition of Science! For Parties! Until next time witches and warlocks.