topic 1 - energy: conservation and dissipation of energy Flashcards
What three things can energy do according to the conservation of energy principle?
Be transferred usefully, stored or dissipated.
What two things cannot happen to energy according to the conservation of energy principle?
It can’t be created or destroyed.
When energy is transferred between stores, what always happens to some of it?
It gets dissipated.
What is dissipated energy?
Energy that is being stored in a way that is not useful (e.g. thermal stores).
Give an example of an system in any object where energy is dissipated to prove that there is no net change to the total energy.
Any valid example including:
A mobile phone (useful chemical energy, wasted thermal energy)
Cold spoon being put into hot soup (useful thermal energy of soup, wasted thermal energy of spoon)
Whenever something moves, why is energy dissipated?
There is usually at least one frictional force acting against the object.
How can lubrication reduce unwanted energy transfers?
They reduce the frictional force between objects so less energy is dissipated into thermal energy stores.
How does the use of thermal insulation in houses reduce unwanted energy transfers?
Thick walls made from a material with low thermal conductivity slows the rate of energy transfer (so the building will cool more slowly).
What is conduction?
The process where vibrating particles transfer energy to neighbouring particles.
When an object has a high thermal conductivity, how does this affect conduction?
It increases the rate of energy transfer by conduction across the material.
What are cavity walls and how do they slow the rate of cooling in a building?
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 through the walls.
Which medium does conduction mainly occur in?
Solids.
What is convection?
Where energectic particles move from hotter to colder regions.
Which mediums does convection only occur in?
Liquids and gases.
In conduction and convection, which store is energy transferred to and which store is it shared across
Transferred to thermal energy store and shared across kinetic energy store.
