ES 2.3 LESSON What is Energy?

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• Energy is the capacity to do work.

– Kinetic energy (associated with motion):

• Examples: flowing water, speeding car, electricity, wind

• Thermal energy (heat): total kinetic energy of all the

moving atoms, ions, or molecules in a sample of
matter, measured as temperature

• Electromagnetic radiation: wave energy resulting from

changes in electrical/magnetic fields; includes solar
energy, which fuels life on Earth

– Potential energy (stored energy):

• Can be converted to kinetic energy

2.3 What Is Energy?

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Electromagnetic Radiation

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• High-quality, or concentrated energy, has a high capacity to do useful work.

– Examples: high-temperature thermal energy, concentrated sunlight,

high-speed wind, energy released from burning fuels)

• Low-quality, or dispersed energy, has little capacity to do

useful work.

Energy Quality

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• First law of thermodynamics (law of conservation of energy)

– Whenever energy is converted from one form to another in a

physical or chemical change, no energy is created or destroyed.

• Second law of thermodynamics

– When energy is changed from one form to another, it always

results in less high-quality energy.

Energy Changes Are Governed By Two Scientific Laws