Energy is transferred when things happen. Energy transferred by a force is called work done
work done(J) =force (N) * distance moved in the direction of the force (m)
when a system changes: energy is transferred: into/away from system, between different objects in a system or between different types of energy stores whenever a system changes - some energy is dissipated and stored in less useful ways
where there are energy transfers in a closed system there is no net change to the total energy in that system
an energy system can be changed through work done by forces, in electrical equipment and in heating
work done (J) = Force (N) * Distance moved in the direction of the force (m)
Energy Transferred = work done
mechanically: when a force acts on a body, energy can be transferred between two stores-electrically: electricity can transfer energy from a power source, delivering it to components within a circuit -heating: thermal energy can be transferred from place to place by the processes of conduction, convection and thermal radiation
consider a car moving at speed-the car applies the brakes and comes to a stop-in doing so, energy in the car's kinetic store is transferred mechanically into a thermal store in the brakes
Change in GPE (J) = mass (kg) * Gravitational field strength (N/Kg) * Change in Vertical height (m)
KE = 1/2 * m * v^2
-whenever energy is transformed, some of the original energy usually ends up in an unwanted [wasted] form-a light bulb e.g. will produce unwanted heat in addition to light
Mechanical processes become wasteful when they cause a rise in temperature, due to friction. This heat will then dissipate into the environment
Power is the rate at which energy is transferred machines for example car engines transfer energy from one type to another every second
Power (W) = Work Done (J) / time taken (s)
One watt is equal to one joule per second J/s
Efficiency = useful energy transferred by the device / total energy transferred by the device