Just about everything in the universe, every clump of matter, every molecule, every atom, exhibits a property known as static electricity. But what exactly is static electricity? Where does it come from, and what causes the effect?
By 600 BCE, naturalists discovered that if you rubbed a piece of amber with cat's fur, the amber would attract small bits and pieces of paper. For these ancient scientists static electricity was pure magic. For more than two millennia, investigators were intrigued, mystified, and amused with the properties of static electricity. In the 18th century, Ben Franklin would first attempt some serious science with respect to the phenomenon, flying his kite in a thunderstorm to capture and quantify the mysterious manifestation. Franklin went on to invent the lightening rod, the Franklin stove, bifocal glasses, and a number of other novel devices, but he never really understood static electricity.
In the latter 18th century, physicist Charles Coulomb defined the laws of attraction and repulsion of electrical charges, but still did not understand what caused them. Many other scientists, Galvani, Volt, Faraday, Edison and Tesla to name a few, would contribute bits and pieces to human understanding of static electricity. But it wasn't until the early years of the 20th century, when Earnest B. Rutherford built his theory of atomic structure, based in large part on the work of physicists Neils Bohr, Max Planck and Werner Heisenberg, that an understanding of static electricity emerged in the continuum of human conscious contemplation.
Rutherford's theory posited, that an atom consisted of a positively charged nucleus surrounded by a field of negatively charged electrons, held together by a status of mutual attraction of opposing electrical charges. This attraction was initially named after Charles Coulomb as the Coulomb force, but today it is more generally known as the electromagnetic force. Each atom of matter consists of neutrons (uncharged particles), protons (positively charged particles) and electrons (negatively charged particles. The neutrons are a combination of protons and electrons held together by the weak nuclear force, and protons are quarks and gluons held together by the strong nuclear force. The number of protons in the nucleus of an atom establishes its elemental properties and results in net positive charge of the atomic nucleus. In an unionized state, the electrons with are equal in number to the protons, exhibit a new negative charge and orbit the nucleus at relatively great distance.
The nucleus of an atom, to achieve electrical stability(an overall null electrical potential or charge), attracts a number of electrons equal to the number of protons. The electrons are distributed in what are referred to as shells or levels, labeled K,L,M,N,P and Q. The K shell, closest to an atoms nucleus, can never hold more than two electrons. The remaining shells can hold differing quantities of electrons, but the outermost shell of a given atom can never hold more than 8 electrons. Interestingly, even though the electrical charge between an atoms nucleus and electron allotment may be null (a number of electrons equal to the number of protons), the atom needs to achieve a status of balance or stability with respect to its outermost shell. The way that a given atom achieves this stability is through Covalent bonding (sharing electrons with other atoms) or ionic bonding (donating electrons to other atoms).
Atoms that are bonded with other atoms are generally considered stable and electrical charge neutral, and atoms which have not achieved stability carry a net positive or net negative electrical charge. This net charge, referred to as a valance and measured in coulombs, is essentially the property we refer to as static electricity.
Most compounds or substances are charge neutral, but when subjected to friction, as in the case of the cat's fir and amber, electrons are essentially ripped away from them. In this way, a surplus of electrons builds up on the surface of one material while a deficit of electrons occurs on the material which has lost the electrons. A material with a surplus of electrons exhibits a negative static charge while a material with a deficit of electrons represents a positive static charge.
Not all elemental substances are as susceptible to developing net static charges as others. Generally, atoms of elements with 2-3 or 5-7 electrons in their outermost shell are less susceptible to static development. All elements will develop static potentials when enough energy is applied to ionize them, but this could be viewed more as dynamic charging as opposed to static charging. Elements with a single electron in their K shell (hydrogen being the only one with this configuration) and elements with four electrons in their outermost shell, are more susceptible to developing static charges, because they will just as readily give up an electron as accept donated ones to achieve electrical stability.
Carbon, silicon, germanium, tin and lead are all elements with four electrons in their outermost shell. These elements, in addition to displaying a propensity to develop static charges, exhibit some other unique and even bizarre properties. Carbon is the lightest or least dense element of this group having only six neutrons, six protons and subsequently six electrons. Carbon itself as well as many carbon compounds are highly electro-static. The amber, and cats fur mentioned above, are both materials rich in carbon as well as hydrogen. As a result they are very susceptible to developing static electrical charges. While these are examples of materials which exhibit pronounced electro-static properties it is important to note that electrostatic charges can develop on the surface of almost any material. For instance, the wing of an aircraft which is primarily an alloy of aluminum and magnesium, can build up a tremendous static potential as it moves through the air. For this reason, an airplane's wing incorporates little wires on its trailing edge to dissipate the charge back into the air. Next time you fly, look at the wing and you will see them there.
Most of us have felt the instant exhilaration of a static electric discharge when getting up out of a chair while wearing something made of wool or polyester fiber. If you ever have the chance to go into a very dark room and after allowing your eyes to adjust, remove a sweater you are wearing, you will be treated to a static electricity light show. Humid air conducts electricity better than dry air does, so you may have noticed static electricity build up is more of a problem on dry days than it is on rainy days. So why do we witness perhaps the most profound exhibition of static electricity, lightening, on rainy days?
Warm moist air is actually less dense than dryer cooler air and therefore is lighter as well. As a result, warm moist air rises in a process called convection. When a plume of war moist air rises in the atmosphere and gets high enough up where the atmosphere is much cooler, the water vapor of the warm moist air condenses into water droplets. These water droplets, now denser and heavier than the air around them, begin to fall back to Earth. With respect to the moisture plume, the shaft of ascending warm moist air is in the middle of the plume and the cooler falling water droplets are on the periphery of it. Thus, there is one mass of moist air rising rapidly and a cooler mass of air and water droplets falling in the opposite direction right next to it. Needless to say, the warm rising air rips electrons off of the cooler descending molecules of air and water and carries them to the top of the forming cloud. When the static negative electrical potential at the top of the cloud become strong enough, a lightening discharge occurs.
A lightening discharge is incredibly hot, many times hotter than even the surface of the Sun. Fortunately it is also very brief, just a few milliseconds, because electricity (electrons) travel at almost the speed of light. Interestingly, bolts of lightening in a thunderstorm superheat the air around them fueling the air convection going on in the cloud. The result is that even greater static potentials develop.
Thousands of years ago, humans had no understanding at all of what was going on in the world they found themselves in. To these ancient folk, thunder, lightening and what caused them were a great enigma and they had little resources to comprehend them. They thought the stars and planets in the sky were deities responsible for many such phenomena they otherwise had no wherewithal to explain. Today, through the diligent efforts of some astute individuals, we know that lightening and thunder are simply a discharge of massive static electrical charges that build up in clouds. Not only have we learned what static electricity is and what causes it, we have harnessed the power of electricity and put it to work improving almost every aspect of human existence.