Topic 1 - Work, Energy and Power Flashcards
1What is a closed system
A system in which neither energy nor matter can enter or leave. Net change is always zero.
What happens when a system changes
Energy is transferred between different stores when work is done by a force or by a current flowing.
Baby Bouncer Question
The baby initially has GPE, when he moves down the GPE is mechanically converted into the baby’s KE and the spring’s EPE. At the end, all the energy is stored as EPE in the spring
Collision between car and wall
Energy transferred mechanically from KE of car to TE of car and wall. Some energy will also be transferred away as sound waves.
Conservation of Energy
Energy cannot be created or destroyed, only stored transferred usefully or dissipated.
Dissipated energy
Whenever there is a change in system, some of the energy transferred is dissipated. This is ‘wasted’ energy as it is not transferred to useful stores.
Kinetic energy
1/2 x mass x (velocity)^2
1/2mv^2
GPE
mass x gravitational field strength x height
mgh
EPE
1/2 x spring constant x extension^2 (m)
Specific Heat Capacity
How much energy it takes to heat 1kg of the material by 1 degree celsius.
ΔE = mcΔt
change in energy = mass x specific heat capacity x change in temp
power
energy transferred / time
How does conduction work
-When one part of an object is heated, its particles gain more kinetic energy.
- These particles vibrate more and collide with neighbouring particles, transferring kinetic energy to them.
- These collisions cause the kinetic energy to spread through the object’s particles, and by extension heat.
How can you keep your house warm in winter?
Thick walls with low thermal conductivity , as it reduces energy transferred away from the house due to its insulating properties
How does lubrication reduce the amount of energy dissipated
Lubricating reduces work done against friction between objects’ surfaces.
This reduces the amount of energy dissipated as thermal energy of surroundings
This increases the efficiency.
efficiency
useful energy output/ total energy input
Non - renewable resource
They aren’t being made at the same rate as they are being used and will run out one day.
Renewable resource
They are made at the same rate or faster than they are used and will therefore never run out.
Non - renewable ( examples)
Fossil fuels and nuclear fuel
Renewable ( examples )
Wind, Solar, Geothermal, waves, Hydroelectricity, Biofuels
Fossil fuels
advantages - reliable, abundant, readily available
disadvantages- non-renewable, produces CO2 emissions that contribute to global warming
Nuclear fuel
advantages - doesn’t produce CO2 emissions, reliable, readily available
disadvantages - non-renewable, produces toxic waste that is hard to store, carries risk of major catastrophe like Chernobyl
Wind
advantages - renewable, no CO2emissions
disadvantages - unreliable: needs wind, produces lot of noise
Solar
advantages - renewable, no CO2 emissions
disadvantages - unreliable: needs sun, only works in day
Geothermal
advantages - renewable, no CO2 emissions, reliable
disadvantages - not many suitable locations, high set up cost
Hydroelectric
advantages - renewable, can respond immediately to increased demand, generally reliable
disadvantages - flooding of valley causes rotting vegetation, loss of habitat
Wave
advantages - renewable, no CO2 emissions
disadvantages - unreliable : waves die out quickly, produces little energy comparatively
Biofuel
advantages - renewable, reliable: can be grown all year round
disadvantages - produces CO2 emissions, cost to refine them is high