1.2 conservation & dissipation of energy

what is the law of conservation of energy?

energy can be transferred usefully, stored, or dissipated, but it cannot be created or destroyed

give an example of energy conservation in a pendulum

at the top: maximum gravitational potential energy; middle: energy transfers to kinetic energy; bottom: maximum kinetic energy; back up: kinetic energy transfers to gravitational potential energy

what effect does friction have on energy?

it transfers energy to thermal stores, causing energy to be dissipated and less useful

how can we reduce unwanted energy transfers?

reduce friction using lubricants (e.g., oil) or removing particles from around moving parts

what is thermal conductivity?

the higher it is, the faster energy transfers by conduction across a material

how do modern houses reduce thermal energy loss?

use materials with low thermal conductivity, build thick walls, fill wall cavities with insulating material, and use double-glazed windows

what is efficiency?

percentage of input energy that is transferred into useful energy

equation for efficiency?

efficiency = useful output ÷ total input (energy or power)

give an example of increasing efficiency in heating water

use a pan with a bigger base and a lid to reduce heat lost to air, or use an electric kettle (heating element inside water + plastic has lower conductivity than metal)