Topic 8 Energy - forces doing work

• 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