Children's Museum of Houston

Static Shock

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The one thing that really bugs me in the winter?  Not so much the cold, but always getting that little “ZAP” when I get out of the car.  So why do we get zapped when we get out of the car and why mostly only during the winter?  Of course, I also sometimes get a similar zap when walking around the Children’s Museum of Houston and then touching a doorknob.

First, we need to understand the nature of the “zap.”   The zap is a discharge of static electricity that has built up as we are riding around.  Atoms, the very tiny particles that make up all matter, are themselves composed of three main particles: protons (with a positive charge), neutrons (with no charge), and electrons (with a negative charge).  The protons and neutrons are located in the center of the atom and the electrons orbit the atom.

When some substances rub together (like our clothes and car seats), electrons are transferred from one substance to the other.  The substance that gains electrons develops a negative charge and the substance that loses electrons gains a positive charge.  That different in charge is STATIC ELECTRICITY!  And, when the charges equalize back out, you get the “zap” in the form of a static discharge.

So what does the cold have to do with it?  On cold days, the humidity in the air is lower due to the lower temperature.  As the temperature of air lowers, less water vapor can be dispersed in the air as compared to when it is warm (this is also why your lips chap more during cold weather).  Humidity is the enemy to the build-up of a static charge.  So, the drier the air, the more static charge can build up, and thus the larger the discharge.  Let’s do a little experiment to see the effects of static electricity.

What You Need:

• Balloon
• Puffed Rice Cereal (like Rice Krispies®)
• Hair or a wool or felt cloth

What To Do:

• Pour some puffed rice cereal onto a table
• Inflate the balloon
• Rub it against your hair (or a piece of wool or felt cloth)
• Slowly lower it towards the puffed rice cereal.  What happens?

What’s Going On?

You can’t see static electricity.  But, we can see the effects of static electricity once the charges build up.  When you rub the balloon against your hair, it picks up electrons, becoming negatively charged.  This static electric charge affects the cereal and causes it to jump around, often sticking to the balloon.

Some people may be asking right now, “but we can see the spark in the ‘zap’ we get when we shock ourselves.  And we can see lightning.  Aren’t those static electricity?”  Well, yes and no.  They are caused by the discharge of electrons from the negative to the positive charge build-up.  So they are CAUSED by static electricity, but are not directly static electricity.  In fact, they represent the end of a build-up of static electricity, for the “zap” removes the excess electrons and re-equalizes the charges back to neutral.