30 Jun, 2013
PRESENTATION: When an inflated balloon is rubbed with a wool cloth, this acquires a net charge that induces another charge of the opposite sign in another material that is put in contact with it. If this material is light enough (for instance some pieces of paper) it will be attracted by the balloon.
- Electrostatics with Computer-Interfaced Charge Sensors, Robert A. Morse, Phys. Teach. 44, 498 (2006)
- Knock off the match, Martin Gardner, Phys. Teach. 38, 191 (2000)
INTRODUCTION: All we see is formed by small particles called atoms, which are composed of even smaller parts called protons, electrons and neutrons. One of the forms of differentiating them is by means of their charge. Protons have it positive, electrons negative, and neutrons neuter. In general, the atoms have the same number of electrons and protons, but if an object is rubbed against another the electrons can pass from one to the other. When the charges are separated in this way we call ecstatic electricity. Two objects with opposite or different charges attract each other or pull towards themselves. The objects with the same charge repel each other or push one from the other far away. A charged object will also attract something with a neutral charge.
OBJECTIVE: To test the behaviour of a charged balloon.
MATERIALS: balloon, wool jumper.
SETUP: We first inflate a balloon, and later on we rub it against a wool jumper so that it can acquire a charge. Once charged we approach it to different objects (hair, paper pieces, water, a wall….) to test the repulsion and attraction that takes place between them.
EXPLANATION: If a balloon is charged, it picks up extra electrons and acquires a negative charge. Keeping it by a neuter object it will make the charges in this object move. If it is a conductor, many electrons will move easily towards the opposite side. If it is an insulator, the electrons of the atoms and the molecules can only move very slightly towards one side, far from the balloon. I any case, there are more positive charges near the negative balloon and, as the opposites attract each other, the balloon is stuck.
CONCEPTS: static electricity, atom charge, electrostatic field, repulsion, attraction.
- YOUTUBE 1
- YOUTUBE 2
- PHYSLET (How to make a balloon stick to a wall)
- Tipler P.A. Física, Reverté, 2010.
- Fowler R.J, Electricidad: Principios y Aplicaciones, Reverté, 1994.
- González Cabrera V.M., Física Fundamental, Progreso, 1974.
- Enríquez Harper G., Fundamentos de Electricidad, Limusa, 1994.
STUDENTS 2012-2013: Natalia Cid, Alba conde, Sandra Correa, Charles De Araujo.
LINK pdf STUDENTS (In Spanish):