How can soap change the pull across a water surface?
The classic kitchen-sink magic trick: shake pepper on a dish of water, touch the middle with a soapy fingertip, and watch every speck flee to the rim in an instant — plus a water bug standing on a pond, or water piling up over a too-full glass.
Talk about it
- Shake pepper onto a dish of water and watch it float. Before you touch it with a soapy finger, guess out loud what the flakes will do.
- Nothing pushed the pepper — so what did the soap actually change? Try to say it in one sentence.
- A bug stands on clean water but sinks when soap is added. What does that tell us about what was holding the bug up?