We all know we need to be washing our hands more thoroughly. It would be nice if it didn't take an actual pandemic to get people to wash their hands after they went for a pee, but there we are.
Getting your kids to wash their hands is a whole other matter entirely, as I'm sure a lot of people with kids will have found. One time, for instance, I asked my nephew to wash his hands and he went into the bathroom and made tap sound effects with his mouth.
Well, an elementary school teacher has found a much more effective method for getting kids to clean the dirt and germs off their hands. You only need a bit of pepper (to represent germs), and some soap and water (to represent soap and water).
The kids (in case you're one of those maniacs that watch videos with the sound off) are pretty pleased by the results when they dip their finger in the soap and the pepper flees like people do these days when someone coughs on a bus.
Adults are impressed too.
Obviously the real reason that the pepper scatters is that the soap breaks the surface tension of the water.
The pepper floats on top of the water because it's hydrophobic. Water molecules like to cling to each other via hydrogen bonds, creating a cohesive force similar to an elastic membrane, which is called surface tension. It allows water to resist external forces, such as the weight of something floating on the surface, and allows it to cling together as water droplets. Soap is really good at breaking the surface tension of water, which is part of what makes it so good at cleaning. When you put your soapy finger into the water, it changes the surface tension. The water molecules want to keep the surface tension going, so they move away from the soap and take the pepper along with them.
But that's basically a fun science lesson for when they're older; right now it's mainly incredibly useful for tricking kids into washing their hands more. You can explain the real reason to them once we're through the pandemic.