Energy Stores, Transfers, and Conservation

Vocabulary flashcards covering key definitions, energy stores, equations, units, and energy sources from the physics lecture transcript.

Energy

An idea represented by a number that indicates what will happen when objects interact in a system; it cannot be created or destroyed and is measured in joules.

Conservation of energy

The law stating that total energy in any interaction between objects is always conserved, meaning it cannot be created or destroyed.

Energy stores

The formal term preferred by exam boards for types of energy whose amounts change when objects interact.

Kinetic energy

The store of energy an object has when it moves, calculated using the equation $\frac{1}{2}mv^2$, where $m$ is mass in kilograms and $v$ is velocity or speed.

Gravitational potential energy (GPE)

The store of energy associated with an object's height, calculated using $mgh$ (mass in kilograms multiplied by gravitational field strength and change in height in meters).

Gravitational field strength ($g$)

A value of either $9.8\,\text{N/kg}$ or $10\,\text{N/kg}$ that is multiplied by mass and height to calculate gravitational potential energy.

Elastic potential energy

The energy stored in a stretched or compressed object like a spring, calculated as $\frac{1}{2}ke^2$.

Spring constant ($k$)

A measure of a spring's stiffness, measured in newtons per meter ($\text{N/m}$), used to calculate elastic potential energy.

Extension ($e$)

The distance in meters that a spring has stretched beyond its original length.

Specific heat capacity ($c$)

The amount of energy required to raise the temperature of $1\,\text{kg}$ of a substance by $1^\circ\text{C}$.

Chemical potential energy

A store of energy found within substances such as food and fuels.

Closed system

A system in which no energy enters from the surroundings and no energy is lost to the surroundings, allowing initial and final energy quantities to be equated.

Work

Another term for energy used, such as energy used against air resistance or friction.

Power ($P$)

The rate of energy transferred, calculated by dividing energy by time ($P = \frac{E}{t}$).

Watt ($\text{W}$)

The unit of measurement for power, which is equivalent to one joule per second ($\text{J/s}$).

Efficiency

A measure of how much supplied energy or power is transferred usefully, calculated as useful output divided by total input.

Energy sources

The resources from which energy is harnessed from the world around us, distinct from energy stores.

Finite energy sources

Nonrenewable energy sources that cannot be replenished once used up, including fossil fuels (coal, oil, gas) and nuclear fuels such as uranium.

Renewable energy sources

Energy sources that do not run out, such as wind power, hydroelectric power, solar panels, and geothermal power.

Biofuel

Any biological matter that is burned to produce energy.