Rolf herds coins, repelling them with an electrically charged ruler.
Charged plastic will attract the surface of water into a visible bump.
A PVC or other small plastic object like a credit
card or a ruler.
Wool, hair, or paper
A nearly full container of water.
To Do and Notice
Look across the surface of the water and notice the reflections of the background.
Rub the plastic with the wool until it is crackling with electric charge and bring it near the surface of the water.
Notice how the reflections in the water change as the water rises to form a lump under the charged plastic.
What's Going on?
Electrically charged things like the plastic attract electrically neutral things like the water. The water rises up against gravity and forms a lump. The lump in the water affects the way the water reflects the scene beyond.
This was discovered during class by Rolf who noticed that when he brought a charged plastic ruler close to a floating aluminum coin the coin was repelled by the ruler!
Actually, the charged ruler was making a mound in the surface of the water and the coins were sliding down the water mound under gravity, surfing coins.
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Scientific Explorations with Paul Doherty
1 Feb 2000