several questions on an experiment on electrostatics


by iknownth
Tags: electrostatics
iknownth
iknownth is offline
#1
Nov29-12, 07:24 AM
P: 16
Move a can without touching it
1. Place an empty aluminium can on a table so that it can roll freely.
2. Rub an inflated rubber balloon on your hair.
3. Hold the rubbed balloon several centimetres away from the can and move it away from the can slowly.
4. Put the balloon on the opposite side and see if the trick still works.

My questions:
1) What makes an object roll? It is obvious that a heavy object cannot roll easily, so, can the mass of an object determine whether it can roll or not?
2) Is the rubbing effect in step 2 still significant for steps 3 & 4?
3) "The aluminium can is an neutral object and the rubber balloon is positively charged after rubbing with hair. Thus, it can attract the aluminium can." Is it what the experiment what to imply?

Thanks in advance.
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HallsofIvy
HallsofIvy is offline
#2
Nov29-12, 07:39 AM
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PF Gold
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Where did you get these questions? They look an awful lot like basic homework questions. If so, this should be in the "homework" section. Even if not, it won't do you any good for someone else to answer them until after you have thought about it for a while yourself. Do you know anything about "electro-statics"? Do you know what "induced charge" is? What do you think is happening here?
iknownth
iknownth is offline
#3
Nov29-12, 07:48 AM
P: 16
......
These are my questions and I have thought about it for some time. I really don't understand. "The aluminium can is an neutral object and the rubber balloon is positively charged after rubbing with hair. Thus, it can attract the aluminium can." This is what I think is happening here. I just know that there is charging by rubbing and an attraction between a neutral object and a charged object.

HallsofIvy
HallsofIvy is offline
#4
Nov29-12, 07:54 AM
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PF Gold
P: 38,879

several questions on an experiment on electrostatics


Do you know what "induced charge" is? Yes, rubbing the balloon on your hair transfers some electrons from the balloon to you hair, leaving your hair (temporarily) negatively charged and the balloon positively charged. When you hold the balloon near the neutral can, the balloon attracts electron in the can so that the side of the can nearest the balloon becomes negatively charged (it is important here that electrons can move freely in metals), so that the can itself acts as if it were negatively charged.
iknownth
iknownth is offline
#5
Nov29-12, 08:09 AM
P: 16
The balloon becomes positively charged temporarily, then why can steps 3 & 4 of the experiment still be carried out?
How do we know if an object becomes positively charged or negatively charged? By the triboelectric series, rubber should be more likely to gain electrons. Should the balloon be negatively charged? Does the charge matters?
Can you also answer my first question? What makes an object roll?


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