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physics > Energy > Flashcards

Energy Flashcards

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AP® Physics flashcards Physics 101 flashcards
1
Q

what is the law of conservation of energy?

A

energy is never created or destroyed, only transferred.

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2
Q

what is the equation for kinetic energy?

A

1/2 x mass, m x speed^2, v^2

kinetic energy measured in joules,
mass measured in kg
speed in m/s^2

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3
Q

what is the equation for work done?

A

work done, W = force, F x distance, s

distance measured in metres,
work done in joules,
force in newtons

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4
Q

equation for weight

A

mass x gravitational field strength.

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5
Q

change in gravitational potential energy

A
  1. weight x change in height
  2. mass, m x gfs, g x change in height
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6
Q

equation for elastic potential energy

A

1/2 x spring constant, k x extension^2, e^2

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7
Q

what are the three ways heat can be transferred by?

A
  • convection
  • conduction
  • radiation
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8
Q

how is heat transferred in solids?

A

by conduction

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9
Q

how is heat transferred in fluids?

A

by convection

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10
Q

how is heat transferred in empty space?

A

by radiation

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11
Q

what happens in conduction?

A

vibrating particles transfer energy to nearby particles

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12
Q

how does conduction work?

(3 marker)

A
  • the vibrating particles gain kinetic energy by heating up
  • these particles collide more with nearby particles and this repeats
  • the heat is then spread out evenly.
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13
Q

why does conduction occur mainly in solids?

(2 marker)

A
  • the particles are tightly packed together
  • this means there would be more collisions that pass on the energy.
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14
Q

define thermal conductivity

A

how well objects transfer thermal energy by conduction.

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15
Q

give one example of an object with high thermal conductivity

A

metal

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16
Q

give one example of an object with low thermal conductivity

A

plastic

17
Q

how does convection work?

(4 marker)

A
  • the particles gain kinetic energy and begin to collide more frequently and forcefully.
  • by the process of random diffusion the particles with energy move away from the warmer side to the cooler side.
  • this means that the particles in the warmer region are more spread out than the particles in the cooler side.
  • therefore, the fluid on the warmer side expands and becomes less dense than the fluid on the cooler side.
18
Q

how is a convection current formed?

(3 marker)

A
  • when the fluid is heated, the warmer particles spread out and are on top of the cooler particles as they become less dense.
  • however they lose the warmth as they are further from the source of heat
  • so the cooler particles become heated again and this process repeats
  • this forms a convection current.
19
Q

how can we reduce convection?

A
  • stop the free flow of fluids
20
Q

how can radiation be carried if not by particles?

A

by infrared waves

21
Q

how can we reduce energy loss?

A
  • thermal insulation
  • lubrication
22
Q

how would sealing the house shut reduce heat loss?

A

air wouldnt be able to pass out by convection.

23
Q

how can we seal the the house?

A

using foam seals

24
Q

how can we reduce heat loss by conduction?

A
  • using cavity walls
  • using double glazed windows
25
Q

how do cavity walls reduce heat loss?

(2 marker)

A
  • they have an air gap between two layers of brick walls which traps the air.
  • air is a poor thermal conductor
26
Q

why is an air gap not efficient in cavity walls?

A

heat can travel through air by convection

27
Q

how do we fix the air gap?

A

fill the gap with insulating foam

this reduces heat loss by both convection and conduction

28
Q

how is double glazing efficient?

(3 marker)

A
  • it is essentially 2 panes of windows with an air gap between them
  • air is a poor thermal conductor
  • therefore heat loss by conduction is reduced.
29
Q

why is friction not useful?

A

friction reduces the efficiency of energy transfer

30
Q

how can we reduce friction?

A

-using oil
-making planes and cars more streamlined

streamlined to reduce friction with air resistance, therefore less fuel.

31
Q

how do wind turbines work?

(3 marker)

A
  • as the turbine spins, the generator also turns
  • the kinetic energy is transferred to electrical energy
  • this is sent to the national grid.

physics (7 decks)

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