If you’re anything like me, you’ve likely experienced a few extra zaps as you go throughout your day.
You reach for a doorknob, touch a TV screen, or even pet your beloved dog or cat and are rewarded with a surprising jolt of electricity.
Lately, it’s hard to get through a single day without getting shocked. But why?
What causes static electricity and why does it seem to intensify over the winter months?
What is Static Electricity?
Static electricity results from the buildup of electrical charges on objects. This electrical charge buildup occurs due to processes that occur at the atomic level.
Static Electricity Happens at the Atomic Level
All matter is made up of atoms.
Each atom contains three types of particles: protons, neutrons, and electrons. Two of these particles are electrically charged: protons have a positive charge and electrons have a negative charge. (Neutrons have no charge and are electrically neutral).
Despite the fact that they are made up of charged particles, atoms have no net charge due to the fact that the number of protons and electrons within an atom are equal. In other words, atoms contain an equal number of positively-charged protons and negatively-charged electrons and the equal number of opposite charges cancel each other out.
While an atom’s protons and neutrons reside in the center (or nucleus) of an atom, its electrons are constantly moving.
Not only can electrons move within an atom, they can also “jump” from one atom to another. The ability of electrons to move from atom to atom gives rise to electricity and is the basis for chemical reactions.
Not surprisingly, it is also the tendency of electrons to move that results in static electricity.
When an electron jumps from one atom to another, it upsets the charge balance of both atoms. Consider the following figure, in which an electron from a sodium (Na) atom jumps to a chlorine (Cl) atom:
Let’s look at what happens to each atom during the process:
Before the electron jump, both the sodium and chlorine atoms are electrically neutral since they contain an equal number of positively-charged protons and negatively-charged electrons.
Following the electron transfer, the sodium atom (now called an ion) gains a charge of +1 since its protons now outnumber its electrons by one. Likewise, the chlorine ion gains a charge of -1 due to the fact that it now has 18 electrons and only 17 protons.
Electrons are constantly jumping from atom to atom, resulting in the formation of charged ions. Remember, static electricity results from the buildup of electrical charges on objects. These charge buildups are the direct result of electrons jumping from atom to atom within different objects. When a positively-charged object gets near a negatively-charged object, electrons will jump from the object with the negative charge to the one with the positive charge in order to restore a neutral charge to each object.
Static shocks are due to the electrons jumping from one object to another.
You likely have noticed that you don’t get a shock when you touch everything (thank goodness!). Instead it seems that only touching certain objects triggers a static electricity discharge.
Why is that?
Insulators, Conductors, and the Triboelectric Effect
Materials can be classified as either insulators or conductors (of electricity, heat, etc.). Conductors are made up of atoms that allow electrons to flow freely from particle to particle. If a conductor becomes charged, the charge is quickly distributed across the entire surface of the object through the movement of electrons. In contrast, insulators are made up of atoms that restrict the flow of electrons from atom to atom.
Even though the atoms within insulators restrict the flow of electrons, insulators can still become charged.
However, when an insulator becomes charged, the charge remains localized to one region within the material. The charge will build up in an insulator rather than spreading through the material and diffusing as the same charge would in a conductor.
When two materials are rubbed together, the friction generated by the rubbing causes electrons to jump from the atoms of one material to atoms in the other material. Consequently, one material will become positively charged while the other material will become negatively charged. This phenomenon is called the triboelectric effect (“tribo” means relating to friction).
Scientists have compiled a list of materials arranged by how likely each material is to become positively or negatively charged due to rubbing. An abridged form of this Triboelectric Series of some common insulators is shown in the figure above.
If two of the insulators from the list are rubbed together, both objects will become charged. The item higher on the list will become positively charged, while the item lower on the list will become negatively charged.
This explains why you get flyaway hair when you pull off a wool sweater. As the wool rubs against your hair when you remove your sweater, your hair becomes positively charged while your sweater becomes negatively charged. Oftentimes, your hair will seem “drawn” to the sweater. This is because opposite charges attract, and the electrons from the sweater seek to travel back to the atoms of your hair in order to restore a neutral charge.
Why is Static Electricity Worse in the Winter?
If electrons are constantly jumping from the atoms of one material to the atoms of another, why do we tend to get more static shocks in the winter than any other time of the year?
It has to do with the amount of moisture in the air.
In the warmer months, the air around us holds much more water and water is an excellent conductor. If any static charge builds up on the objects in our home, the water in the air allows a path for electrons to flow and restore neutral charge to the objects.
This all changes in winter, when the humidity in the air drops.
Cold air isn’t able to hold as much water vapor as warm air.
Without the water in the air, insulating materials in your home build up static charge and are unable to release it.
When you walk across the wool carpet in your rubber-soled shoes, your shoes pick up electrons and become negatively charged. Your body, being over 60% water, is a good conductor and the charge quickly spreads through your body. But without water in the air, the excess electrons can’t flow away from your body to restore neutrality. You reach for a doorknob made of metal (a conductor with an affinity for electrons) and electrons jump from your hand to the doorknob, resulting in a shock.
So what do you do to prevent those uncomfortable shocks?
Buy a humidifier to add some more water vapor to the air of your home. The increased water vapor in the air will allow electrons to flow from charged services, diffusing the static buildup and decreasing the risk of static shocks.
Or, you could always move to my home state of Florida where it seems the humidity is always high.
Having Fun with Static Electricity
Here are some videos showing some fun experiments you can perform to play with static electricity.