Step-by-step tutorial
Step 1
Sprinkle pepper over a bowl of water.
Step 2
APut a tiny bit of dish soap on your finger (or a toothpick).
Step 3
Touch the surface of the water. Watch what happens!
Tip
After a few touches, you’ll need to start over with clean water.
Learn more
This experiment works because water is pretty sticky, and one of its favorite things to stick to is itself! It’s like each water molecule holding hands with all the other water molecules around it. Scientists call this surface tension.
Soap, however, ruins all this happy hand-holding. You can imagine a soap molecule like a tiny connector piece with two different ends. One end wants to grab onto water molecules, while the other end wants to push them away. So once soap is added, the surface tension breaks… but only in that one spot.
The water all around the soapy spot is still holding hands and sticking together. That surface tension stickiness pulls the water towards the edges of the bowl, taking the pepper along with it!