aqa physics - energy transfers in a system

what is the conservation of energy principle?

energy cannot be created or destroyed, only transferred, stored, or dissipated

why is dissipated energy called wasted energy?

it is stored in a way that is not useful, usually in thermal energy stores

why does a phone feel warm after being used for a while?

energy is transferred from the battery's chemical store, but some is dissipated to the phone's thermal energy store

why does soup cool down when a spoon is placed in it inside a sealed flask?

energy is transferred from the soup's thermal store to the spoon's thermal store, but no energy leaves the system, so net change is zero

what is conduction?

the transfer of energy by vibrating particles in solids

how does conduction work?

heated particles vibrate more, colliding with neighboring particles and transferring energy through kinetic stores

what is thermal conductivity?

a measure of how quickly energy is transferred through a material

what is convection?

the movement of energetic particles from hotter to cooler regions in liquids and gases

why does heated fluid become less dense?

particles move faster and spread apart, increasing the space between them

how does a convection current form?

warm, less dense fluid rises, cooler, denser fluid sinks, and the cycle continues if there is a constant heat source

how do radiators heat a room?

warm air rises, cooler air moves in to replace it, creating a convection current

how does lubrication reduce friction?

it reduces friction between surfaces, preventing energy dissipation as heat

what are lubricants usually made of?

liquids like oil that can flow between objects and coat them

how can insulation reduce heat loss in a house?

thick walls with low thermal conductivity slow down energy transfer

how can you investigate thermal insulators?

measure water temperature loss in a sealed container wrapped in different materials

how does insulation thickness affect heat loss?

thicker insulation reduces temperature change, making it a better thermal insulator