Everyday Energy

The everyday magic of energy, with the physics left in

Sunlight crosses empty space, a spinning magnet lights a room, and the calorie on a food label is the heat that would warm a litre of water by one degree Celsius. None of it is magic, and all of it can be measured. Everyday Energy explains how, in plain language, with every figure taken from US government science agencies, NIST or university physics pages.

Start with the forms of energy Open the units table
Drawing on a deep indigo ground: a yellow sun sends wavy rays towards a glowing light bulb, while along the ground a pendulum swings, a spring sits compressed, a small fire burns and a house has a lit window.
Stored energy, moving energy, light, heat and electricity: the cast of every guide on this site.
  1. Energy is stored or movingEvery form is either potential energy, waiting in position or in chemical bonds, or kinetic energy, the energy of motion.
  2. It changes form, never amountEnergy is neither created nor destroyed. What looks like "using it up" is turning it into forms we cannot easily use, mostly heat.
  3. One quantity, many unitsJoules, kilowatt-hours, Btu and food calories all measure the same thing, and fixed factors convert between them.

Six guides, from a rolling ball to the calorie

Each guide stands on its own, but read in order they build from first principles to the electricity meter and the food label. Every guide names the documents it relies on and the date it was last reviewed against them.

  1. The forms of energy: stored and in motion

    Potential and kinetic energy, and the everyday forms within each.

  2. Conversion and conservation: energy changes form, never amount

    Why energy is never used up, only changed, and what efficiency measures.

  3. Sunlight: the energy that crosses empty space

    Fusion in the Sun, light as waves and photons, and the spectrum.

  4. How electricity reaches a home

    Electrons, generators, transformers and the grid, in order.

  5. Energy at home: watts, kilowatt-hours and efficiency

    Power versus energy, the kilowatt-hour, and estimating appliance use.

  6. Energy in food: what a calorie measures

    The calorie as a unit of energy, in joules and in everyday terms.

Physics only, and every number traced to a source

"Energy" is one of the most stretched words in the language. This site uses it in one sense only: the physical quantity that scientists measure in joules. It explains that quantity with the help of the US Energy Information Administration, the National Institute of Standards and Technology, NASA and university physics pages, names the documents on every page, and leaves out anything those sources do not support.

Read the editorial policy

  • Authoritative sources onlyGovernment science and statistics agencies, the national measurement institute and university teaching pages. No blogs, vendors or forums.
  • No invented figuresConversion factors come from NIST or the EIA. Where a page works an example, the arithmetic is shown so it can be checked.
  • Nothing for saleNo utility, energy company or retailer is behind the site. No advertising, affiliate links or product recommendations.

Three conversions worth remembering

  • 3.6 MJin one kilowatt-hour, the unit on an electricity bill
  • 3,412 Btuin one kilowatt-hour, the EIA's factor for comparing fuels
  • 4,184 Jin one thermochemical kilocalorie, the "calorie" of a food label

The units table sets out every energy and power unit used on this site, with its conversion to joules or watts and the document each factor comes from.

Open the energy and power units table