01: energy Flashcards
what is a system?
an object or a group of objects that interact
describe ‘kinetic energy’
[2]
definition: the energy stored in moving objects
equation: Eₖ = ½ x m x v²
describe ‘elastic potential energy’
definition: the energy stored in a (stretched) spring
equation: Eₑ = 1/2 x k (spring constant) x e²
notes: extension is directly proportional to force
describe ‘work’
definition: the transformation of energy from energy one store to another
equation: Work (J) = Force (N) x Distance (m)
describe ‘gravitational potential energy’
definition: the energy stored in an object due to its distance from the earths surface
equation: Eₚ (J) = m (mass kg) x g (gravity n/kg) x h (height m)
describe ‘thermal / internal energy’
definition: energy stored in a system by the particles (total energy of kinetic and potential energy)
equation:
notes: internal energy increases / decreases with temperature
describe ‘specific heat capacity’
definition: the amount of energy to raise the temperature of a substance by 1°c
equation: △e (J) = m (kg) x shc x △θ (°c)
law of conservation of energy
energy can be transferred usefully, stored, or dissipated but not created nor destroyed
describe the kinetic energy and gravitational potential energy transfers within a pendulum (including friction)
highest point: no Ek, maximum Ep
lowest point: maximum Ek, minimum Ep
friction is at the fixed point and also between air particles which causes energy to be dissipated - we can combat this by using lubricants, or removing air particles around the pendulum
describe bungee jumping process
Ep —> Ek —> Ee (when extension occurs) —> Ek —> Ep
energy is dissipated as thermal energy due to friction between air particles, and the stretching effects the bungee rope which is not fully elastic, this causes the bungee jumper to never return to its original position
describe ‘power’
definition: the rate at which energy is transferred / the rate at which work is done
equation: power (W) = energy transferred (J) ÷ time (s)
power (W) = work done (J) ÷ time (s)
notes: 1W = 1J/s
describe ‘efficiency’
definition:
equation: efficiency = useful energy / power output ÷ total energy / power input
notes:
describe ‘thermal conductivity’ and how it relates to building construction
the higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across that material
construct building with low thermal conductivity materials, or with thick walls /windows to reduce rate of thermal energy transfer
describe ‘fossil fuels’
definition: coal, oil, gas
advantages: reliable, release lots of energy, abundant, relatively cheap, versatile
disadvantages: releases lots of CO2, non-renewable, can release other pollutants (diesel - carbon particles, nitrogen oxides, coal - sulfur dioxide (leads to acid rain))
describe ‘nuclear power’
advantages: does not release CO2 (only when being built), reliable
disadvantage: highly dangerous, dismantling takes many years and is expensive, generates large amounts of radioactive waste which must be stored for years before being safe
