# Straws on wall

1. Feb 28, 2013

### Numeriprimi

Hi!
Someone said me, if I take a plastic straw and wipe it with a handkerchief (or something like that), I can recharge it so that it will hang even on some of the walls due to electric charge (but do not know which way, tomorrow I am going to buy some straws:-D)
How would you explain this phenomenon? How big is that electric charge?

2. Feb 28, 2013

### Drakkith

Staff Emeritus
3. Mar 1, 2013

### Numeriprimi

Re: staws on wall

Thanks! :-)
Hmm, it's a lot. And how do you know it?
I ask about eletric charge, so how can I calculate it? From voltage?
Electricity I have not seen since elementary school, so I don't know much.

4. Mar 1, 2013

### Numeriprimi

Re: staws on wall

One element must be charged positively and the other negatively to attract. Straw is positive or negative?

5. Mar 1, 2013

### sophiecentaur

Re: staws on wall

Actually, only one object needs to be charged. A charged comb can pick up uncharged dust because the dust particles become polarised and the nearer (opposite) charge is attracted more than the further (same) charge is repelled - but is further away so the net force is attraction. It's called 'induced charging' and is what's used all over in dust extractors and many other Electrostatic machines.
In the straws case, the straw is charged and the surface of the wall acquires an opposite charge by induction. Hence the sticking.
Before I had it explained, I couldn't figure out how it would work!