Energy

Created by

Rosa Cane-McCree

Cards (24)

what are 8 energy stores
thermal
kinetic
chemical
gravitational
elastic
nuclear
electrostatic
magnetic
what is the law of conservation of energy
energy cannot be created or destroyed. energy can only be transferred between stores
what is a closed system
a system where there is no energy lost by dissipation due to friction or heating
what is an open system
a a system that lets matter and energy in and out
what is the equation for work done
work done = power x time
what is the equation for power
power = (energy)work done / time
what is the equation for cost
cost = work done x cost per unit
what is the equation for specific heat capacity
Energy = mass x specific heat capacity x change in temperature
what is the equation for specific latent heat
Energy = mass x specific latent heat
what is dissipation
the transfer of energy to stores that aren't useful (surroundings)
explain the dissipation of a car engine due to friction
the chemical energy used in the engine dissipates into thermal energy due to friction as the parts of the engine heat up
explain the dissipation of kettle water and the plastic of the kettle
the thermal energy from the water dissipates into the surrounding (the plastic wall of the kettle) as thermal energy as the kettle heats up
name 2 ways you can reduce dissipation + give an example
dissipation of friction: lubrication (e.g oiling an engine)
dissipation of heat: insulation (e.g double glazing glass on windows)
how does the thickness of the wall in a house affect the rate of cooling
thinner walls will take a shorter time to cool down rather than thicker walls meaning the rate of temperature drop increases
how does the thermal conductivity of the walls in a house affect the rate of cooling  
the walls with the higher thermal conductivity will cool down faster meaning the rate of temperature drop is greater
how do you calculate efficiency
efficiency = (useful output energy transfer / input energy transfer ) x 100
how can you increase efficiency and explain
by reducing the wasted energy
use insulation to reduce heating the surroundings
make devices from materials that reduce unwanted energy transfer
use technology to produce devices that are better at their jobs
analyse the energy transfer of a car at the start and end of a race (in an open system)
Start:
no kinetic energy (its stationary)
lots of chemical energy (more fuel)
some thermal energy (dissipated due to friction of the engine)
End:
lots of kinetic energy (moving)
less chemical energy (loss of fuel)
more thermal energy (more friction and sound energy causes dissipation)
analyse the energy transfer of a car breaking
Moving:
kinetic energy (it's moving)
less thermal energy (cool surroundings)
Breaking:
no kinetic energy (stopped moving)
more thermal energy (break pads heat the surroundings)
analyse the energy transfer of a gymnast running onto a spring board
above the springboard:
no elastic energy (uncompressed springs)
lots of kinetic energy (running)
lots of gravitational potential (jumping)
on the springboard:
lots of elastic energy (compressed springs)
no kinetic energy (stationary)
less gravitational potential (lower height)
analyse the energy transfer of someone throwing a tennis ball upwards(in an open system)
left the hand:
lots of kinetic energy (moving)
less gravitational potential (closer to the earth)
less thermal energy (colder surroundings)
stationary in the air:
no kinetic energy (stationary)
more gravitational potential (further from the earth)
more thermal energy (air resistance heats up the surroundings)
analyse the energy transfer of a pair of sunglasses falling onto sand
just before they land:
lots of kinetic energy (moving)
less thermal energy (cooler sand and air)
on the sand:
no kinetic energy (stationary)
more thermal energy (warmer sand and air)
analyse the energy transfer of an electric kettle boiling water
when the kettle is turned on:
more chemical energy (more fuel and oxygen)
less thermal energy (cold water)
when the water is boiled:
less chemical energy (less fuel and oxygen)
more thermal energy (boiled water)
analyse the energy transfer of a storage heater (heats concrete block at night and warms a room at day)
start of the day:
more thermal energy of concrete (hot piece of concrete)
less thermal energy of room (cold room)
end of the day:
less thermal energy of concrete (cold piece of concrete)
more thermal energy of room (warm room)