energy stores and systems

what is a system

an object or group of objects that interact

when is energy stored?

when a system changes

examples of energy being stored

• throwing an object upwards - before the ball leaves your hand, it has a store of kinetic energy. at its highest point, it has a store of gravitational energy. when you catch it again, it has a store of kinetic energy.

• boiling water in a kettle - when you turn it on, the water gets hotter. there is more thermal energy stored in the hot water than there was in the hot water

what are examples of energy stores?

• kinetic

• thermal

• chemical

• gravitational

• magnetic

• electrostatic

• elastic potential

• nuclear

how is energy measured?

in joules (J), kilojoules (kJ), or megajoules (MJ)

what is the conservation of energy?

the concept that the amount of energy always stays the same. it can be transferred from one store to another, but never created or destroyed

what are the ways energy is transferred?

• mechanical (work is done by a force)

• electrically (work is done by moving charge)

• heating

what is the equation to calculate kinetic energy

kinetic energy (J) = ½ x mass (kg) x (speed)² (m/s)²

what is the formula to find elastic potential energy?

elastic potential energy (J) = ½ x spring constant (N/m) x extension (m)