The Magic of Electric Force
Topics Covered: Electric Charge, Electric Force
Let’s say you have two plastic rods. Hang one rod from a thread, and slowly bring another plastic rod near the first. What do you think would happen? Duh, you say, nothing would happen. But what if you vigorously rub both rods with wool and repeat the same process? Surprisingly, you will find that two rods repel each other. Seems like magic! But why? In this lesson, we’ll get into some basics of magical concepts of electrostatics and electrical charges.
In our little experiment, the rods and wool are initially neutral. In physics, being “neutral” means that both the rods and the wool have equal amounts of positive and negative charges. Since both are neutral, putting two neutral objects near each other would not change anything.
However, when we rub the plastic rod and wool together, the negative charge moves from the wool to the rod. The electrons will move from the wool to the rod, which leaves the rod with extra negative charges and wool with excess positive charges!
Now, when we use the charge diagram, we typically only draw the excess charges. This means now the wool is left only with the positive charges and the rod is left with only the negative charges. In other words, both the wool and rod are now charged. So when you put two charged rods next to each other, they will repel each other— because like charges repel, and opposite charges attract.
This force that exists between two rods is called electric force. Electric force is a force that exists between charged objects, and can be repulsive or attractive. Objects with like charges (-- or ++) experience repulsive electric force, while the objects with opposite charges (+-) experience attractive electric force.
This phenomenon can be seen in other objects as well. When you rub the balloon against your hair, it will cause the electrons to move from your hair to the balloon. Since the balloon now has a negative charge and hair has a positive charge (since it lost electrons), your hair will get pulled toward the balloon! What a cool magic of physics!
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