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Lesson 0: Introduction to energy use (60-90 min)

Energy types and transformations

Discussion:

Ask the class to brainstorm: what is energy? Use this brainstorming session to develop a list of ways in which energy can be used: playing football, eating, growing plants, charging cell phones, using cell phones, talking about energy, etc.

The scientific definition of energy is “the ability to do work.” Work is defined by any force that moves an object in the direction of that force, and is equal to force times displacement (W=F*d). When you lift a banana off the ground, you’re doing work against the downward force of gravity. And lifting a banana takes energy— so energy allows you to do things that wouldn’t happen by themselves.

Energy can be either kinetic (energy in action) or potential (stored energy). When you hold a banana above the ground, that banana has potential energy; when you release it, gravity pulls the banana and it gains kinetic energy as it speeds up toward the ground.

All of the energy in the world falls into several categories: Heat Light (or sound) Motion (kinetic) Electrical Chemical Nuclear Gravitational Choose several of students’ examples of energy use, and have the class think about all the energy transformations involved:

When a student talks in class, she uses electrical energy to make her brain think and her muscles move. This electrical energy comes from her body, which runs on chemical energy from digesting food. The plants that she ate used light energy from the sun to grow, and the sun uses nuclear energy that it creates by fusing atoms together. The energy in these atoms has been around since the beginning of the universe!

Energy use around the world

Students estimate how much energy they personally use in one day, and how this compares to their peers around the world.

Considering units The basic unit of energy is called a joule. When you pick up a banana from the ground and put it on your desk, you use 1 joule of energy. When you lift 100 bananas up to a table, you use 100 joules of energy. Your body uses a lot of energy: if you stand absolutely still, everything that happens inside you (digesting food, thinking, breathing, pumping blood, etc) requires 100 joules of energy every second! This is why your body feels warm all the time—a lot of the energy you’re using is transformed into heat, which heats up your clothes and anything you touch.

Discuss how much energy other things use: if you talk on a cell phone for 10 minutes, your phone uses 1000 J of electrical energy. A candy bar contains 1 million J when you digest it; you usually talk about food in terms of kilocalories (or Calories in the US), and 1 kcal equals 4,200 joules. An average lightening bolt contains 100 million J of electrical energy, which turns into light, heat, and sound when the lightening hits something.

Here are some other examples:

Activity: As homework, ask students to record how much energy they directly consume in a single day. This includes the food they eat, the electricity they use, and all cooking, heating, and transportation fuels. Ask students to figure out where their electricity comes from: is there hydropower nearby? A coal power plant? Attach a spreadsheet with how much energy (in KJ) is required for a number of common tasks. Also attach a few example energy-use sheets: one from Tanzania, one from China, one from Europe, and one from the US.

The next day, discuss students’ results and compare their energy use to students from other backgrounds.

Not counting food, the average person in the US uses 359 GJ every day, and the average European uses 154 GJ. The average person in China uses 54 GJ, and the average person in Africa uses only 17 GJ daily. Ask students to brainstorm the reasons for these differences. Do Africans use less light, or heat the water when they bathe? How do people in the US wash their clothes and sweep their houses? Do you think most urban Chinese live in big houses, which need more heating during the winter, or small houses? Assume that both Europe and the US have very similar lifestyles—which continent do you think requires more efficient electrical devices? Which continent has bigger houses?

**There could be another unit here on ways to generate electricity and comparing energy sources. This could include discussions like: as Africa becomes more developed, what kinds of power plants will people build? Where is there a lot of wind, and where is there a lot of sun?

Solar Details: In the entire world, human use 4.88*1020J of energy every year (not counting food). But this is only 1/10,000 of the amount of solar energy that hits the planet in a year!!

Here is a graph of hours of perpendicular sunshine vs time of year:

[cite 8.21 Physics of Energy source] Lambda, or longitude, is the angle of a line drawn from the equator to any specific location on the planet. http://eev3.liu.edu/ee0406/nstar/Polaris/polaris1/latitudemain.htm Today, most of the people using solar energy for electricity live in Europe, the US, and China where lambda is around 40˚. Does this make sense? Why isn’t solar energy more popular near the equator?

Challenges with solar energy: you only get energy during the day, so you’ll need to store that energy in batteries when it’s not available it’s expensive to turn light into electricity, because the technology is still relatively new it’s easier to have a lot of small solar power plants rather than one large solar power plant, so everyone involved needs to know how to run the system