Practically every one of us has experienced the effects of static electricity, and it is an experience we can see, feel, and sometimes even hear. The classic example of static electricity is of course when you walk across the carpet, then reach for the doorknob and receive a shock. Another way we experience static electricity is when you slide down a plastic slide then come out with your hair standing straight up. Some of us have even witnessed a car go up in flames while the driver is filling up their car with gasoline. In The Flying Circus of Physics, there is yet another real life example of static electricity. One day, a professor was driving slowly alongside two of his friends who were in another car matching his speed. While the car was still moving, the professor’s friend in the passenger side of the other car reached out to hand him a package of gum. When the separation between their hands lessened to a few centimeters, a “terrific discharge“ occurred between them, which left them temporarily disabled. Thankfully, the professor regained his senses and was able to control the car before anyone was hurt, but we are left to wonder why this disabling spark occurred. What is it that can shock your finger, make your hair stand straight up, start a fire, or in this case shock you enough to temporarily disable you?
To understand this, we first need to look at what a charge is. The world is made up of atoms which are broken down even further into positively charged protons, negatively charged electrons, and neutrons, which have no charge. When we rub things together, electrons can move from one atom to another. Some atoms then have extra electrons, and a negative charge. Other atoms lose electrons, and they have a positive charge. This is what we call static electricity. If two things have different charges, they will be attracted and pull towards each other. If two things have the same charge, they will repel, and push away from each other. So when you go down a slide it rubs against your hair and electrons are moved from your hair to the slide. This leaves your hair with the same positive charge, so they want to repel each other, and the farthest they can get is to stand up and away from all the other hairs. You’re probably wondering how this is applied to the exchange of gum scenario. Well, it is an extremely similar situation. The professor and the passenger of the other car had different charges. So when they reached out to exchange the gum, a spark was created when the electrons from one hand jumped through the air to reach the other hand. The electrons did this because the charges between the two were not balanced, and the charge difference needed to be reduced.
However, this explanation still doesn’t clarify everything that happened with the shocking exchange of gum. Why is it that the professor and the passenger of the other car had different charges when they were both riding in a car? When people experience a shock as they get out of their car, they often blame it on the car itself. However, it is not that the car is charged, but the body. The author of Humans and Sparks, William Beaty, clarifies this idea by explaining that the cause of car sparking is contact-electrification between insulating surfaces, followed by separation of those surfaces. He goes on to explain that the passenger in the car is one surface, and the car seat is the other. So when you sit on a plastic car seat, the contact between your clothes and the seat’s surface causes the electrical charges within atoms of the material to transfer between surfaces. Therefore, one surface ends up with more negative charges than positive. When the professor and the passenger of the other car reached out to exchange the gum, the different charges equalized by leaping through the air, shocking both of them. Their movement in the car, what they were wearing, and the interior of the car all could have contributed to the difference in their charges. All of this ultimately resulted in the shocking exchange of gum.
Here is a link to a study conducted by John Chubb Instrumentation that was done in order to discover what factors, such as the type of clothing and the type of car seat, affect the body voltage when getting out of a car.
The Control of Body Voltage Getting Out of a Car
Listed below is a link to a video of others who have experienced the pain that often comes along with static electricity.
Beaty, William. "Humans and Sparks." Preventing Painful High-Voltage Electrostatic Doorknob Sparks. 1997. Web. 17 Oct 2009.
This is William Beaty’s article that explains the cause of static electricity, how to stop the pain, and how to prevent it. He also talks about “Electric People” in this article. However, his explanation of the cause of static electricity was of the most help to me. He had a very in-depth explanation of why car door sparks occur, which is directly related to the question I was trying to answer. I found this source to be credible, because at the bottom of the webpage he gave his contact information, and there was also a link to his biography. It listed all of his credentials, as well as what he has written in the past. Overall I found this website to be useful, but I wasn’t able to use the entire article, because he spent a lot of time talking about “Electric People”.
Chubb, John. "The Control of Body Voltage Getting Out of a Car." John Chubb Instrumentation. 1998. Web. 17 Oct 2009.
This was a link provided by William Beaty’s article. It is the description of an experiment that was conducted in order to measure the electrostatic voltages generated on a person getting out of a car. This study matches my question perfectly, and helped to confirm my explanation. I believe this article to be credible, because it explains where they got all of their information, how they conducted the experiment, and also how the experiment can be replicated.
Gonick, Larry, and Art Huffman. The Cartoon Guide to Physics. New York, NY: HarperPerennial, 1991. Print.>
This is one of the books we use in PHYS 1090. I found Chapter 12, Charges, to be very helpful when answering my question. Even though the explanation in this book was rather brief, it explained the basic concepts that I needed in a clear and understandable way. I found this source to be extremely credible, because it is the book we use in our class, and there is also a biography about both of the authors in the back of the book. Art Huffman is very qualified to write a guide to physics.
Henderson, Tom. "Static Electricity." The Physics Classroom. Web. 17 Oct 2009.
I found this website to be extremely helpful. It is full of very valuable information, and the concepts were explained very clearly. I was able to learn a lot from this website, and it helped me to better answer my question. There was even a quiz at the end of each section, to check understanding. I found this source to be very reliable. The website included his biography, as well as a place where I could contact him to ask questions and give him feedback.
Safety At Gas Stations-Static Effect! Be Aware![Video].(2006).Retrieved October 21,2009, from http://www.youtube.com/watch?v=AFKrlPUSBJU&feature=related.
I felt this video did a great job of showing what can happen at a gas station due to static electricity.
Walker, Jearl. The Flying Circus of Physics. 2nd ed. 1977. Print.
This is the book that I originally retrieved the question from, and it also included a brief answer.