energy (p1) Flashcards
1
Q
describe elastic potential energy:
A
- when stretching the spring, we’re applying a force to change the length
- this is called ‘doing work’
- we’re putting energy in to stretch the spring. the spring is storing the energy. this is called elastic potential energy
- the spring’s extension and the force applied is directly proportional. however, applying too much force to the spring will make it reach its limit of proportionality, where it can’t stretch anymore
2
Q
list all of the energy stores (8):
A
- thermal (heat energy trapped in object. related to its temperature)
- kinetic
- gravitational potential energy
- elastic potential energy
- chemical energy (held in chemical bonds)
- magnetic energy
- electrostatic energy
- nuclear energy
3
Q
what are the 4 ways to transfer energy?
A
- mechanically (e.g. by stretching elastic band)
- electrically (e.g. plugging something into a socket)
- by heating
- by radiation (light/sound waves, infrared radiation)
4
Q
what has happened when a system has changed?
A
energy has been transferred. either from object to object or between different energy stores
5
Q
what is the difference between an open and closed system?
A
open: the matter can exchange energy with the outside world. can lose/gain energy
closed: separate from outside world. neither matter/energy can enter/leave. energy can be transferred within, but the overall change is always 0
6
Q
define mechanical ‘work done’:
A
energy transferred (required) when a force is used to move an object over a distance
- essentially, work is done when energy is transferred from one store to another
- measured in joules
7
Q
define electrical ‘work done’:
A
when current flows. the energy required to overcome the resistance in the wires of a circuit
- calculated by: energy = potential difference x current x time (power x time)
8
Q
how do you calculate work done?
A
force x distance (along line of action of the force)
9
Q
describe the concept of mechanical work done using a train slowing down:
A
train slowing down. applies brakes, causing friction between the brakes and the wheels. the friction does work, as it slows the train down. causes energy in the wheels’ kinetic energy stores to be transferred to the thermal energy stores of the surroundings in the form of heat
10
Q
describe the energy transfers in a coal fire:
A
- coal has a large store of chemical energy
- when coal is burned, the chemical energy is transferred by heating to the thermal energy store of the coal
- hot coals and flames transfer energy to the surroundings by heating and radiation
11
Q
describe the energy transfers when:
an archer pulls the string of a bow back and loads an arrow. the archer then releases the string allowing the arrow to fire
A
- as the string of the bow is pulled back, chemical energy in the archer’s muscles is transferred mechanically to the elastic potential of the bow
- when the archer releases the string of the bow, the elastic potential energy of the string is transferred mechanically to the kinetic energy store of the arrow
12
Q
what is gravity?
A
the force of attraction between two objects, with the size of the force depending on the mass of the two objects and their distance apart
13
Q
what is a gravitational field?
A
the field of influence/attraction around an object. the earth’s gravitational field strength is 9.8N/kg
- larger objects have a larger gravitational field
14
Q
what is an object’s weight?
A
refers to the force acting on an object due to gravity. therefore an object’s weight can change depending on the gravitational field strength. measured in newtons
- weight = mass x gravitational field strength
15
Q
describe gravitational potential energy:
A
- the energy stored in an object due to its position above the Earth’s surface
- this is from the force of gravity acting on the object
16
Q
define specific heat capacity:
A
the energy required to raise the temperature of 1kg of a substance by 1 degree celsius
- can also be the energy released as 1kg of a substance cools by 1 degree
- a material with a higher specific heat capacity requires more energy to change its temperature
17
Q
how is heat transferred in solids?
A
conduction
- As one end of a solid object is heated, energy is transferred to the kinetic energy stores of the particles in that end.
- This causes the particles to vibrate faster, and so they collide with their neighbouring particles more often.
- As the collisions transfer kinetic energy, their neighbours also vibrate faster and collide more often with their neighbours.
- This process repeats over and over again so that energy is effectively passed along the object from one particle to the next.
- Even though it’s kinetic energy that’s being passed between particles, when considering the object as a whole we say that it’s heat (or thermal energy) that’s being transferred.
- mainly occurs in solids as the particles are so close together
18
Q
what is thermal conductivity?
A
how well objects transfer energy by conduction
19
Q
what is convection?
A
- occurs mainly in fluids
- the particles gain energy from heating and move around faster. these more energetic particles move away from the warmer region and towards the cooler region
- the particles in the warmer region are more spread out than those in the cooler region. the fluid in the warmer region expands and becomes less dense than the cooler fluid
20
Q
what is a convection current?
A
heat the bottom of a container of fluid
- heating the container means the particles near the heat source gain kinetic energy and spread out, becoming less dense
- they therefore rise above the colder less dense particles, and these sink and take their place
- the hotter particles lose their energy and cool down, while the cooler particles heat up
- this cycle keeps repeating for as long as the fluid is being heated, and if it occurs in a limited space (e.g. container/room), it causes a convection current
21
Q
how do we reduce convection?
A
stop the free flow of fluids
22
Q
what are the differences and similarities between conduction and convection?
A
both involve particles gaining kinetic energy
- in conduction, only the energy is transferred
- in convection, the particles themselves move
23
Q
how would heat energy be transferred without particles (in a vacuum)?
A
through radiation, by infrared waves. the hotter an object is, the more infrared radiation it emits
24
Q
what is internal energy?
A
the energy stored by the particles making up a substance/system
- made up of the potential (gravitational/elastic) energy stores and kinetic energy stores
25
what happens when we heat an object?
transfer energy to kinetic energy store of particles, increasing their internal energy, read as an increase in temperature
- temperature is simply a measure of the average internal energy of a substance
- some materials require much more energy to increase its temperature than others
26
define power:
- power is the rate at which energy is transferred or at the rate at which work is done
- power is measured in watts.
- an energy transfer of one joule per second is equal to 1 watt.
27
what are the power equations?
power = energy transferred / time
OR
power = work done / time
28
what is the law of conservation of energy?
energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed
29
describe the relationship between thermal conductivity and energy transfer:
the higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material.
30
name some ways to prevent a house from becoming thermally conductive:
- reduce unwanted energy transfers
- walls are made out of an external brick wall and an internal breezeblock. this is very thermally conductive, so the cavity in the middle is packed with insulation (therefore no convection/conduction) - CAVITY WALLS. thick walls also work
- single glazed = one pane of glass, double glazed = two panes. both reduce heat loss through convection. double glazed windows have a small air gap between the two panes, minimising conduction (air is a poor heat conductor)
- loft insulation
31
how to reduce convection in a house:
seal the house closed, to prevent air from moving in and out, as this would lose heat through convection. use foam seals around doors
32
define efficiency:
the proportion of the energy supplied that is transferred into a useful energy output
- most devices aren't 100% efficient
33
what is the efficiency equation?
efficiency = useful energy output / total energy input
OR
efficiency = useful power output / total power input
34
what is a renewable energy source?
- an energy source that is being (or can be) replenished as it is being used.
35
name some uses of energy sources:
- transport
- electricity
- generation
- heating
36
evaluate the use of fossil fuels:
advantages:
- reliable (can be used in any conditions)
- release a great deal of energy (e.g. good for aeroplanes)
- abundant and relatively cheap
- versatile (very useful for powering vehicles)
- most of our current infrastructure is designed to run using fossil fuels (e.g. cars use petrol/diesel)
disadvantages:
- releases carbon dioxide (climate change)
- non-renewable
- can release other pollutants (e.g. diesel releases carbon monoxide and nitrogen and sulfur oxides)
37
describe nuclear power:
- generates electricity
- obtained from nuclear reactions, such as nuclear fission reactions in nuclear power stations
38
evaluate nuclear energy:
advantage:
- don't produce pollutants like sulfur dioxide or greenhouse gases like carbon dioxide
- can be used in any conditions
- although it's a limited resource (uranium), it probably won't run out for a very long time
disadvantage:
- technically a finite resource
- produce radioactive waste, which remains harmful for thousands of years so must be stored carefully
- quite expensive (decommissioning)
- a problem at the power station could lead to a small chance of a nuclear meltdown, which could release large amounts of nuclear waste into the environment
39
evaluate wind and solar energy resources:
advantage:
- renewable (obviously)
- don't release carbon dioxide/pollutants
- low running costs
- don't damage the environment
disadvantage:
- wind and solar aren't reliable (dependent on the weather). also can't increase supply during peak demand
- high upfront costs
- the process of building them generally does release pollutants
- take up lots of space, need so many to create enough power
- people complain that wind turbines don't look nice/are too noisy
40
describe wind power:
- captured through the use of wind turbines, placed in exposed areas with strong winds
- each turbine has a generator inside it, and as the blades spin in the wind, they turn the generator
- the generator converts the kinetic energy from the movement into electrical energy, which can then be transported to the national grid
41
describe solar power:
- solar cells/panels generate electric currents directly from sunlight
- they work well in low energy devices and in remote regions which aren't connected to the national grid
- however, solar energy is now being used on much larger scales
42
what is geothermal power?
- geothermal energy is generated and stored in the Earth's crust. originates from the initial formation of the planet, and the ongoing radioactive decay of materials e.g. uranium in the earth
- can be used either directly for heat (pump water down to the ground, allowing it to heat up, then pumping it back up to the surface, much cheaper) or to generate electricity (leave the water underground until it's heated up so much that it's converted to steam, and as this rises, it turns turbines, which drives generators to produce electricity)
43
evaluate geothermal power:
advantage:
- installing the plant only damages the environment very slightly
- while running, doesn't produce any pollutants/carbon dioxide
- renewable resource
- reliable
disadvantage:
- can only be used in certain areas, e.g. volcanic regions, where hot rocks lie near the surface
- the power plants required can be quite expensive to build
44
describe bio-fuels:
- other renewable energy sources only generate electricity, and we cannot always use this for transport
- biofuels are produced from recently living organisms (plants/algae, as they photosynthesise and have the sun's energy locked up inside them, which can be released when we burn them), and don't add co2 to the climate (carbon neutral)
- however, to grow the crops to create bio-fuels, it will take up food growing space, which may increase the price of food even more
45
evaluate biofuels:
advantages:
- renewable resource, can be grown again and again
- relatively cheap
- easy to transport
- can be mixed with fossil fuels like petrol. can benefit from them, without having to buy new cars
disadvantages:
- must convert natural land to grow the biofuels (deforestation). damaging to environment, releases carbon dioxide
- the harvesting, processing and transportation of plants releases more carbon dioxide
46
describe hydroelectric dams and tidal barrages:
- big dam that prevents water from flowing like it should. higher water level on one side than the other
- the difference in water levels means the stored water has huge amounts of GPE, which can be converted into electricity
- the force of the water being released form the reservoirs behind the dams, spins turbines inside the dams. these are connected to generators, which generate electricity when they spin
HE: trapping water coming from upstream, preventing it from continuing its journey to the ocean. accumulates a reservoir
tidal: makes use of tides. twice a day is high tide. the barrage traps the water as it comes in (high tide), and gradually releases it during low tide
47
evaluate hydroelectric dams and tidal barrages:
advantages:
- both generate large amounts of energy with no pollution
- both reliable
- HE can provide an immediate response to increased demand
- fairly low running costs
- work on both large and small scales
disadvantages:
- big impact on surrounding environment (HE especially, often flood huge areas, can submerge important habitats and villages)
- both can stop boats and fish from travelling up and down the river, negatively affecting fish migrations
- the initial setup of both is expensive
48
describe wave power, and evaluate it:
the water in the sea rises and falls due to waves. wave machines use the kinetic energy in this movement to drive electricity generators
advantages:
- renewable energy resource, no fuel costs
- no harmful polluting gases produced
disadvantages:
- difficult to scale up the designs to produce large amounts of electricity
- having many wave machines can negatively affect wildlife
49
what is a system?
a system is an object or a group of objects.
- e.g. in a pendulum, the objects in the system would be the mass, string, and the fixed point at the top. air particles could also be considered part of the system.
50
describe the forces acting on an object when it is moving, then it hits an obstacle:
- initially has a lot of kinetic energy, allowing it to move.
- when it hits the obstacle, the kinetic energy is immediately transferred into other stores, such as thermal energy and sound waves to the surroundings.
51
describe the forces acting on an object when it is being accelerated by a constant force:
- energy is required to accelerate the object (chemical, thermal, electrical).
- this energy will then gradually convert into kinetic energy, gradually increasing the velocity of the object, therefore accelerating it.
52
what is the equation for kinetic energy?
- kinetic energy = 0.5 x mass x (speed)^2
- kinetic energy = joules (J)
- mass = kilograms (kg)
- speed = m/s
53
what is the equation for gravitational potential energy?
- G.P.E = mass x gravitational field strength x height
- G.P.E = joules (J)
- mass = kilograms (kg)
- height = metres (m)
- gravitational field strength = newtons per kilogram (N/kg)
54
what is the equation for specific heat capacity?
- change in thermal energy = mass x specific heat capacity x temperature change
- change in thermal energy = joules (J)
- mass = kilograms (kg)
- specific heat capacity = joules per kilogram degrees celsius
- temperature change = degrees celsius)
55
what are the two equations for power?
1. power = energy transferred / time
2. power = work done / time
- power = watts (W)
- energy transferred = joules (J)
- time = seconds (s)
- work done = joules (J)
56
give an example to describe power:
- consider a weight-lifting scenario.
- two individuals lift the same weight over their heads, but one does it faster than the other, the one who lifted the weight more swiftly has exerted more power.
- they have done the same amount of work in less time, hence, they have a higher power output.
57
describe energy transfers in a closed system:
- energy can be transferred in a closed system.
- since energy cannot exchange with the surroundings, there will be no net change with the total energy in the system.
- e.g. adding ice cubes to a bottle of water and closing the lid is an energy transfer.
- assuming the water bottle doesn't exchange any energy with its surroundings, and that it's a closed system
- the water will exchange thermal energy with the ice cubes, so the water will cool down.
58
describe lubrication as a method of reducing unwanted energy transfer:
- energy can be lost due to friction.
- when riding a bike, the chain will produce a lot of friction.
- in order to combat this, place oil (a lubricant) on the chain.
- this will stop the chain from experiencing so much friction (makes it easier to pedal), and will maintain the bike in the long run.
59
what is friction?
the resistance something encounters when moving over a solid or through a liquid
- negative thing, as it reduces the efficiency of energy transfer, meaning some can be lost as heat
60
describe streamlining as a method of reducing unwanted energy transfer:
- when objects travel through the air, they experience a contact force called air resistance.
- to combat this, we streamline objects.
- changing the shape of an object streamlines it, to reduce friction from air resistance
- this means it can use less fuel
61
what are the equations for efficiency?
1. efficiency = useful output energy transfer / total input energy transfer
2. efficiency = useful power output / total power input
62
what are the main energy resources available for use on Earth (11, 3 of which are fossil fuels):
- fossil fuels: coal, oil, gas
- nuclear fuel
- bio-fuel
- wind
- hydro-electricity
- geothermal
- tidal
- solar
- waves
63
describe the patterns and trends in the use of energy resources:
- over the past 20 years, there has been a gradual shift towards cleaner technologies.
- government grants have encouraged the use of wind and solar energy farms.
- coal has gradually been replaced with cleaner natural gas.
- a new gen of nuclear power stations is currently in development.
64
what is the kinetic energy of an object?
the energy it possesses, due to its motion. depends on its speed and mass
- higher the speed, higher the kinetic energy
- higher the mass, higher the kinetic energy, as long as everything else is kept equal
65
what is nuclear energy?
the energy stored in the nucleus of an atom which can be released through radioactive decay
66
what is most of our energy used for in the UK today?
- domestic uses. natural gas for heating (the gas is burned for hot water, then pumped into radiators). coal can also be burned in fireplaces. there are also solar water heaters, and biofuels can be burned for heat
- transport. petrol/diesel/kerosene, from oil - fossil fuels. trains used to be powered by coal, but are not mostly electric. increase in use of biofuels (renewable) and electric cars
67
what is a fossil fuel?
- a hydrocarbon containing material formed naturally in the Earth's crust from the remains of dead plants and animals
- the three types: coal, crude oil, natural gas
- they may be burned to provide heat, either for: direct use (e.g. cooking), to power engines, to generate electricity
