Activity Based Science Learning >The rotating straw


Introduction:

As we know, by rubbing or induction electric charge can be produced. By combing your hair you must have tried to attract small pieces of paper. You must also be knowing that charges are of two types- positive charge and negative charge. Like changes repel while unlike charges attract each other. We shall see this with the help of an interesting experiment. 

Required Material:

Two straws (used for sipping cold drinks), a bottle having a plane surface which has negligible friction. 

Procedure:

1.         Take a plastic bottle whose cap is plane.

2.         Take two drinking straws and by holding them from one end rub them well two or three times with the help of a handkerchief.

3.         Now, place one of the straws on the top of the bottle cap in such a manner that it remains parallel to the ground and its middle portion sits on the top of the cap.

4.         Now take the other straw, holding it from one end bring it near the first straw.

5.         As soon as the second straw is brought near the straw resting on the bottle, the latter moves away from the former by rotating on its resting point.

6.         If we keep moving the hand held straw in a circular manner towards the straw on the bottle cap, the latter also continuously keeps getting away. While doing so it also rotates presenting a very interesting view of repulsion.

7.         Now, instead of the second straw being the handkerchief which was used for rubbing the straws, towards the first straw.

8.         The first straw now starts getting attracted towards the handkerchief.  Moving the handkerchief away from the straw in a circular manner, the straw also keeps moving towards the handkerchief while making a circular rotation. 

Discussion:

When both the straws are rubbed with a handkerchief, the same kind of charge is developed in them while the opposite charge is produced in the handkerchief. In the first case, as both the straws hold the same kind of charge they repel each other and so the straw resting on the bottle moves away from the hand held straw. In the second case as the charge on the handkerchief has a sign opposite to that on the straw, the handkerchief and the straw attract each other, Therefore, the straw on the bottle moves towards the handkerchief.

The place where the straw rests on the bottle the friction between the cap and the straw should be least there, so that the straw is free to rotate on the cap. 

Do and Think a Little more:

During winter people are after found rubbing their hands. When you rub your both hands against each other do they develop charges? Devise an experiment which can answer this question.





 


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