Conservation of energy Flashcards
What is the conservation of energy principle?
Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed.
What can power be described as?
The rate of energy transfer/ the rate of doing work.
Conduction
Energy is transferred to the thermal store of the object & shared across the kinetic energy stores of the particles in the object. Happens in solids.
Describe the process of conduction.
Particles near the heat source vibrate more & collide with neighbouring particles, transferring energy between their kinetic energy stores & causing them to vibrate too. Process continues thru-out the object until energy is transferred to the other side & then usually to the thermal energy store of the surroundings/ anything touching the object.
Convection
Energetic particles move away from hotter to cooler regions. Happens in gases and liquids.
Describe convection.
Energy is transferred to the particles near the heat source (possibly by conduction) these particles become warmer and less dense. They rise to cooler regions and are replaced by cooler more dense particles. These particles are also heated up at the same time the previously risen air loses energy, cools, becomes denser and sinks. The cycle repeats (convection current)
How can frictional forces be reduced?
Friction causes some energy in the system to be dissipated. When objects are rubbed together, lubricants can be used to reduce the friction between the objects surfaces when they move. Lubricants are usually liquids so they can flow easily between objects and coat them.
How can you prevent heat loss in your house?
. thick walls made from a material with low thermal conductivity ()slows down the rate of energy transfer
. using thermal insulation
What are cavity walls?
Some houses have cavity walls, made up of an inner and outer wall with an air gap in the middle. The air gap reduces the amount of energy transferred by conduction thru the walls.
What is cavity wall insulation?
The cavity wall air gap is filled with foam which can reduce energy transfer by convection in the wall cavity.
What is Loft insulation? What does it do?
Loft insulation can be laid out across the loft floor and ceiling. Fibreglass wool is often used which is a good insulator as it has pockets of trapped air. Loft insulation reduces energy loss by conduction and also helps prevent convection currents from being created.
What are double-glazed windows? How do they work?
They work in the same way as cavity walls - They have an air gap between 2 sheets of glass to prevent energy transfer by conduction through the windows.
What do draught excluders do?
Draught excluders around doors and windows reduce energy transfers by convection.
