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energy Flashcards

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Physics 101 flashcards AP® Physics flashcards
1
Q

define a system

A

an object or group of objects

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2
Q

what happens when a system changes

A

energy is transferred - this can either be into or away from a system, between different objects or between different types of energy stores within a system

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3
Q

what happens when energy is transferred to an object

A

the energy is stored in one of the object’s energy stores

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4
Q

list all energy stores

A

kinetic, thermal, chemical, gravitational potential, elastic potential, electrostatic, magnetic and nuclear

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5
Q

define kinetic energy store

A

energy stored in a moving object

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6
Q

define thermal energy store

A

all objects have thermal energy stores; the higher the temperature, the more thermal energy it stores

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7
Q

define chemical energy store

A

energy stored in substances that can release the energy by a chemical reaction; this includes food, fuels and even our muscles – e.g., chemical energy stored in muscles is transferred to kinetic energy

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8
Q

define gravitational potential energy store

A

it’s stored in objects with mass and are inside a gravitational field

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9
Q

define elastic potential energy store

A

it’s stored in stretched or compressed objects

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10
Q

define electrostatic potential energy store

A

stored in objects with an electric charge interacting with another electric charge

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11
Q

define magnetic energy store

A

stored in magnets that are interacting with other magnetic material

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12
Q

define nuclear energy store

A

energy stored in atomic nuclei released in nuclear reactions

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13
Q

define a closed system

A

a system where neither matter nor energy can enter or leave and so the net change in total energy is always zero

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14
Q

what ways can we transfer energy

A
  • mechanically; doing work by exerting a force on an object and moving it
  • electrically; a current moving through a potential difference can do work
  • by heating; energy can be transferred from a hotter object to a colder object and through radiation when energy is transferred by waves
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15
Q

describe the energy changes when an object is projected upwards

A

the chemical energy store in the person’s muscle decreases and the energy is transferred to the kinetic energy stores of the object. as its altitude increases, the kinetic energy stores decrease as kinetic energy is transferred to gravitational potential energy, so the gravitational potential energy stores increase. some of the kinetic energy is dissipated as thermal energy to the surroundings due to air resistance acting on the object

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16
Q

describe the energy changes when a moving object hits an obstacle

A

the kinetic energy decreases as it is transferred to the thermal energy stores of the obstacle due to friction. the thermal energy stores of the obstacle increase, leading to the energy being dissipated

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17
Q

describe the energy changes when a vehicle slows down

A

kinetic energy is transferred to the thermal energy store in the brake pads. the energy is dissipated as kinetic energy stores of the car decrease and thermal energy stores in the breaks increase due to work being done by friction

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18
Q

describe the energy changes when bringing water to a boil in a kettle

A

energy is transferred from the electrostatic stores in the wires to thermal energy in the heating element. this thermal energy is transferred to the thermal energy stores in the water, causing it to boil

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19
Q

why is no device 100% efficient

A

some energy is always dissipated when an energy transfer takes place – the energy is wasted/stored in a way that is not useful (dissipation is usually by energy transfer to the thermal energy stores of the surroundings)

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20
Q

how does the law of conservation of energy explain why total energy in a closed system is always the same

A

no energy can enter or leave the closed system, and, since energy cannot be created or destroyed, the total energy is always the same

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21
Q

what do you assume when using the elastic potential equation

A

that the limit of proportionality has not been exceeded

22
Q

properties of energy

A

it can be transferred usefully, stored or dissipated, but cannot be created or destroyed

23
Q

define power

A

the rate at which energy is transferred or the rate at which work is done

24
Q

what is an energy transfer of 1 joule per second equal to

A

a power of 1 watt

25
Q

give an example that illustrates the definition of power

A

a powerful machine does not necessarily exert a strong force – a powerful machine is one that transfers a lot of energy in a short space of time

e.g., two identical cars that are racing on the same distance along a straight race track to a finish line - the car with the more powerful engine will reach the finish line faster because it will transfer the same amount of energy, but over less time

another example is two electric motors both lifting the same weight through the same height, but the one with the greater power rating lifts it faster

26
Q

the main factors that affect the rate of energy transfer

A

thermal conductivity and thickness of the walls

27
Q

describe the relationship between the rate of energy transfer and thermal conductivity

A

the higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material; i.e. the lower the thermal conductivity, the more well-insulated a house is

28
Q

feature of most houses in relation to thermal conductivity

A

most houses have an internal and external wall with a cavity in between, which forms a relatively high thermal conductivity

29
Q

how can you reduce unwanted energy transfer via thermal conductivity

A
  • by adding cavity wall insulation which has a very low thermal conductivity; this reduces cost of heating because less energy is wasted
  • double-glazed windows have a lower thermal conductivity because of the layer of insulating air between the two layers of glass, which reduces energy transferred by conduction
  • loft insulation e.g. fibreglass has air gaps that give it a low thermal conductivity
  • draught excluders can stop draughts blowing in and out, reducing energy transfer by convection
30
Q

describe the relationship between the rate of energy transfer and thickness of walls

A

the thicker the walls, the slower the rate of unwanted thermal energy transfer; i.e. an ideal house has walls with a low thermal conductivity and very thick walls

31
Q

how do lubricants work to reduce unwanted energy transfers

A

whenever something moves, frictional forces always act on it that cause energy to be dissipated and transferred to thermal energy stores of the surroundings; lubricants reduce friction between forces when they move so that less energy is transferred to the surroundings

32
Q

what are lubricants

A

substances (usually liquids) that coat objects and flow between the moving parts

33
Q

how do we reduce
- friction
- air-resistance

A

FRICTION: reduced by lubricants
AIR-RESISTANCE: reduced by streamlining

34
Q

define useful devices

A

devices that transfer energy from one energy store to a useful energy store

35
Q

what is the exception to no devices being 100% efficient

A

electric heaters, because all the energy is transferred to the useful thermal energy stores

36
Q

how can efficiency of a device be increased

A

by lubrication or insulation depending on the intended energy transfer

37
Q

name the fossil fuels and their uses

A
  • coal; used for heating and electricity generation
  • oil; used for transport and electricity generation
  • gas; used for heating and electricity generation
38
Q

list the renewable energy resources

A

nuclear, biofuel, wind, hydroelectricity, tidal, geothermal, solar and waves

39
Q

define renewable energy resource

A

an energy resource that is being replenished as it is used up so it will never run out

40
Q

define non-renewable energy resource

A

an energy resource that is not being replenished as quickly as it is used up, so will run out one day

41
Q

pros and cons of renewable energy

A

PROS:
- they will never run out
- they don’t produce greenhouse gases because they don’t release CO₂
- they don’t create radioactive waste products

CONS:
- they still generate pollution
- low-efficiency levels
- can be unreliable
- generally expensive

42
Q

pros of nuclear fuel

A
  • they don’t produce greenhouse gases because they don’t release CO₂
  • it’s more energy rich than fossil fuels
43
Q

what fuels can be used for nuclear power

A

uranium (or plutonium)

44
Q

cons of nuclear fuel

A
  • toxic nuclear waste to dispose of
  • a fire or explosion at a nuclear power station would cause significant environmental damage
45
Q

cons of wind power

A
  • it isn’t always windy
  • it’s expensive to build
46
Q

cons of hydroelectric power

A
  • can damage habitats as it involves damming rivers
47
Q

cons of solar power

A
  • it isn’t always sunny
  • expensive to build
48
Q

cons of geothermal energy

A
  • only certain places can access enough heat
49
Q

cons of tidal energy

A
  • only two tides a day
50
Q

cons of wave energy

A
  • waves vary; not a consistent source of energy
  • they can only be built in certain places
51
Q

pros and cons of biomass

A

PROS:
- carbon neutral

CONS:
- destruction of habitats

52
Q

define specific heat capacity

A

the specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius

physics spec (10 decks)

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