### Sticking to static electricity with Coulomb’s law

This exercise is a part of Educator Guide: Insect Swarms Might Electrify the Sky / View Guide
###### Directions for teachers:

Ask students to read the Science News article “Insect swarms might generate as much electric charge as storm clouds” and answer the following questions. Your students can answer all of the questions on their own or in pairs, or you can walk students through the first set and then have them do the second set on their own. A version of the article, “Insect swarms might electrify the sky,” appears in the December 3, 2022 issue of Science News. Review concepts of static electricity and electric fields if needed.

Want to make it a virtual lesson? Post the online Science News article to your virtual classroom. Discuss the article and questions with your class on your virtual platform.

###### Static electricity explained

Before diving into the fascinating world of electrically charged insects, let’s review some basic science concepts and discuss how we experience the concepts in our daily lives.

Static electricity occurs when a stationary electric charge builds up on the surface of a substance. When two objects have opposite charges (positive and negative), the objects attract. When two objects have the same charge (positive and positive; negative and negative), the objects repel. The force of attraction or repulsion between two charged objects is called Coulomb force, or the electrostatic force.

1. Think of a time when you’ve experienced static electricity. How did you know you experienced it? What action caused it to happen?

Student answers will vary but might mention walking on carpet in socks and seeing a spark when touching a doorknob. Or students might mention having their recently dried clothes stick to them, or having their hair stick out and float away from their head uncontrollably on a cool, dry day.

2. Based on your knowledge of the particles that make up atoms and molecules, explain how charges can build up on surfaces.

Atoms and molecules are made up of protons, neutrons and electrons, and generally exist in nature in a neutrally charged state, meaning they have the same number of electrons as protons. When this balance is disrupted by bumping or rubbing on other atoms, electrons may travel from one surface to another. When this happens, there’s an imbalance of charge on both surfaces. The surface that lost electrons is positive and the surface that gained them is more negative.

3. Explain the science behind your experience of static electricity. Why did your hair stand up or your freshly clean clothes stick to your body? Why did you see a spark when you touched a doorknob, for example?

A stationary electric charge built up between two surfaces, likely from the friction of the surfaces rubbing together. One surface lost electrons and the other surface gained electrons. Surfaces that stick together, such as the clothes on your body and the clothes fresh out of a dryer, had opposite charges. Surfaces that repelled each other, such as hair repelling other hair, had the same charge. Static shocks or sparks resulted from the transfer of electrons from an electron-rich surface to an electron-deficient one.

###### Electric charge in the atmosphere

1. Describe how flying insects generate static electricity. How does this electricity contribute to the electric field of the atmosphere?

Flying insects are constantly bumping into atoms and molecules in the air. This disturbance can move electrons to and from atoms and molecules in the atmosphere, creating a buildup of charge, or a charge potential, and generating static electricity.

2. What is the relationship between the density of an insect swarm and the change in the atmosphere’s electric charge? Based on what you’ve learned so far from this discussion, explain the science behind this relationship.

The denser the swarm, the greater the change in the atmosphere’s electric charge. If there are many insects bumping into air atoms and molecules within the same small area, then the insects will collide with many more air atoms and molecules, disrupting the charge distribution and producing a greater electric charge than just one or a few insects could.

Optional extension: Explain how this relationship relates to Coulomb’s law.

Coulomb’s law states that electrostatic force is greater when charged particles are closer together. Researchers observed that denser swarms generate greater electrostatic force.

3. How does the atmosphere’s electric field impact weather?

The article mentions the atmosphere’s electric field influences how water droplets form, dust particles move and lightning develops.

4. Using the example from the Science News article and your answers above, explain how static electricity helps produce lightning. Tip: If you need more information, use this article from Science News Explores.

As water vapor in the atmosphere condenses to form a cloud, the cloud heats up and rises. The higher the cloud rises, the colder the air gets. Small ice crystals form in the cloud. Winds cause the crystals to collide with water droplets and other particles in the cloud, transferring electric charge. Over time, negative electric charges collect at the bottom of the cloud while positive electric charges collect at the top. Eventually, the difference in electric charge between the ground, which is positively charged, and the cloud’s bottom becomes large enough that the cloud discharges an electric current that we call lightning.

5. Why do you think physicist Joseph Dwyer says that electrically charged flying animals are unlikely to ever reach the density required to produce lightning like storm clouds do?

The electric charge generated by dense swarms probably wouldn’t be large enough to produce lightning.