1. Static Electricity:
* When you comb your hair, the friction between the comb and your hair causes electrons to be transferred from one to the other. Usually, the comb ends up gaining electrons, becoming negatively charged, and your hair loses electrons, becoming positively charged. The type of charge depends on the materials involved; some materials readily gain electrons, while others readily lose them. Common combs made of plastic tend to gain electrons.
2. Water's Polarity:
* Water molecules (H₂O) are polar. This means they have a slightly positive end (near the hydrogen atoms) and a slightly negative end (near the oxygen atom). This uneven distribution of charge is due to oxygen being more electronegative than hydrogen, meaning it pulls the electrons in the covalent bond closer to itself.
3. Electrostatic Attraction in Action:
* When you bring the charged comb (typically negatively charged) near the stream of water:
* The positive ends of the water molecules are attracted to the negative charge of the comb.
* Similarly, if the comb were positively charged (less common, but possible with certain comb materials), the negative ends of the water molecules would be attracted to the comb.
* This attraction causes the stream of water to bend towards the comb. The water molecules are orienting themselves so that their oppositely charged ends are facing the charged comb.
In simpler terms:
Imagine the comb is like a magnet, and the water molecules are like tiny compass needles. The "magnet" (comb) is charged with electricity from rubbing it on your hair. The "compass needles" (water molecules) have a slightly positive and slightly negative end. The opposite charges attract each other, so the water molecules turn towards the comb, causing the water stream to bend.
Important Considerations:
* Dry Air: This effect works best in dry air. Humidity (water vapor in the air) can dissipate the static charge on the comb, reducing the effect.
* Comb Material: The type of material the comb is made of affects how well it holds a static charge. Plastic combs generally work well.
* Cleanliness: A clean comb and clean hair help the charge build up better.
* Charge Strength: The stronger the static charge on the comb, the more dramatic the bending effect will be. Rubbing the comb against your hair for a longer time will usually create a stronger charge.
* Water Stream Thinness: A very thin, controlled stream of water is ideal. Too much water mass makes it harder for the electrostatic force to overcome the water's inertia and surface tension.
Therefore, the bending of water near a comb after it's been run through hair is a classic demonstration of electrostatic forces acting on polar molecules.