P8 - Forces doing Work

• energy of a system can be changed through work done by forces, in electrical equipment, in heating
• units of work done and energy are joules
• work done = force x distance moved in the direction of the force
• power is rate at which energy is transferred or used up
• unit of power is watts (W)
• power = workdone / time taken
• efficiency = useful output / total input
• electrical appliances have an efficiency rating that shows how much energy they use compared with their output
• mechanical processes become wasteful when they cause a rise in temp
• energy is all system changes is dissipated so that it is stored in less useful ways
• Change in GPE = mass x gravity x height
• KE = 1/2 x mass x velocity squared
• in a closed system there is no net change to the total energy in that system