Energy Flashcards
what is the law of conservation of energy?
energy is never created or destroyed, only transferred.
what is the equation for kinetic energy?
1/2 x mass, m x speed^2, v^2
kinetic energy measured in joules,
mass measured in kg
speed in m/s^2
what is the equation for work done?
work done, W = force, F x distance, s
distance measured in metres,
work done in joules,
force in newtons
equation for weight
mass x gravitational field strength.
change in gravitational potential energy
- weight x change in height
- mass, m x gfs, g x change in height
equation for elastic potential energy
1/2 x spring constant, k x extension^2, e^2
what are the three ways heat can be transferred by?
- convection
- conduction
- radiation
how is heat transferred in solids?
by conduction
how is heat transferred in fluids?
by convection
how is heat transferred in empty space?
by radiation
what happens in conduction?
vibrating particles transfer energy to nearby particles
how does conduction work?
(3 marker)
- the vibrating particles gain kinetic energy by heating up
- these particles collide more with nearby particles and this repeats
- the heat is then spread out evenly.
why does conduction occur mainly in solids?
(2 marker)
- the particles are tightly packed together
- this means there would be more collisions that pass on the energy.
define thermal conductivity
how well objects transfer thermal energy by conduction.
give one example of an object with high thermal conductivity
metal
give one example of an object with low thermal conductivity
plastic
how does convection work?
(4 marker)
- the particles gain kinetic energy and begin to collide more frequently and forcefully.
- by the process of random diffusion the particles with energy move away from the warmer side to the cooler side.
- this means that the particles in the warmer region are more spread out than the particles in the cooler side.
- therefore, the fluid on the warmer side expands and becomes less dense than the fluid on the cooler side.
how is a convection current formed?
(3 marker)
- when the fluid is heated, the warmer particles spread out and are on top of the cooler particles as they become less dense.
- however they lose the warmth as they are further from the source of heat
- so the cooler particles become heated again and this process repeats
- this forms a convection current.
how can we reduce convection?
- stop the free flow of fluids
how can radiation be carried if not by particles?
by infrared waves
how can we reduce energy loss?
- thermal insulation
- lubrication
how would sealing the house shut reduce heat loss?
air wouldnt be able to pass out by convection.
how can we seal the the house?
using foam seals
how can we reduce heat loss by conduction?
- using cavity walls
- using double glazed windows
how do cavity walls reduce heat loss?
(2 marker)
- they have an air gap between two layers of brick walls which traps the air.
- air is a poor thermal conductor
why is an air gap not efficient in cavity walls?
heat can travel through air by convection
how do we fix the air gap?
fill the gap with insulating foam
this reduces heat loss by both convection and conduction
how is double glazing efficient?
(3 marker)
- it is essentially 2 panes of windows with an air gap between them
- air is a poor thermal conductor
- therefore heat loss by conduction is reduced.
why is friction not useful?
friction reduces the efficiency of energy transfer
how can we reduce friction?
-using oil
-making planes and cars more streamlined
streamlined to reduce friction with air resistance, therefore less fuel.
how do wind turbines work?
(3 marker)
- as the turbine spins, the generator also turns
- the kinetic energy is transferred to electrical energy
- this is sent to the national grid.
