Energy and Electricity Y9

Question 1

what is the equation for gravitational potential energy

Answer 1

GPE = mass x gravitational field strength x height
( J = kg x N/kg x m)
* on earth the gravitational field strength is 9.8N/kg

Question 2

what is the equation for kinetic energy

Answer 2

KE = 1/2 x mass x speed²
( J = kg x m/s)
* any object that has mass and is moving has KE

Question 3

what is the equation for charge

Question 4

define ‘energy’

Answer 4

• energy is not created or destroyed
• energy does not make things happen
• energy is only noticeable when being transferred
• 8 energy stores
• 5 energy pathways
• measured in Joules

Question 5

name 8 energy stores

Answer 5

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

Question 6

name 5 energy pathways

Answer 6

force, wave, thermal transfer, electric current, chemical reaction

Question 7

describe a chemical energy store

Answer 7

energy stored in chemical bonds, when chemicals react they transfer this energy, eg. food, muscles, coal

Question 8

describe an elastic potential energy store

Answer 8

energy stored when an object is stretched or squashed, energy is transferred when object returns to original shape, eg. catapults, springs, balloons

Question 9

describe a kinetic energy store

Answer 9

the energy in a moving object, larger mass = larger amount of energy, eg. flying arrow, buses, runners

Question 10

describe a gravitational potential energy store

Answer 10

the energy of an object at a height, transferred when object falls and loses height, eg. aeroplanes, mugs on a table, rock on a cliff

Question 11

describe a thermal energy store

Answer 11

the energy of an object due to temperature, hotter objects have particles that vibrate quicker, energy travels from hot object to a cold object, eg. hot water bottle, coffee, human bodies

Question 12

describe a nuclear energy store

Answer 12

energy in the nucleus of an atom, released when atoms split or fuse together, eg. uranium nuclear fuel, the sun

Question 13

describe a magnetic energy store

Answer 13

when an object is affected by a magnetic field, energy is either increased or reduced, eg. repelling poles have been pushed closer together or attracting poles have been pulled further apart

Question 14

describe an electrostatic energy store

Answer 14

energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart, found in electrically charged objects, eg. thunderclouds

Question 15

describe a force energy pathway

Answer 15

the force of gravity, losing GPE and gaining KE, eg. book falling off shelf

Question 16

describe a wave energy pathway

Answer 16

energy transferred as a wave, eg light radiation and emitted from the sun, talking transfers sound waves from throat to ear drum

Question 17

describe a thermal transfer energy pathway

Answer 17

when an object with high temp transfers to object with low temp, due to temperature difference caused electrically or by chemical reaction, eg. coffee getting cold, opening a window

Question 18

describe an electric current energy pathway

Question 19

describe a chemical reaction energy pathway

Question 20

describe efficient/inefficient energy

Answer 20

efficiency = useful energy output/total energy input
* measured as a value between 0 and 1
* cannot exceed 1 as energy is never created
* larger the efficiency number - larger the efficiency
eg.
steam engine has 2000J of energy and transfers to 400J KE and 1600J thermal, this train is inefficient as only kinetic energy is useful to allow movement
bullet train has 1000J of energy and transfers 600J KE and 400J thermal, this train is efficient as less useless thermal energy is created

Question 21

describe the energy in a falling object

Answer 21

• the force of gravity converts GPE into KE
• object has max GPE at top of its fall and max KE just before it hits the floor
• find max GPE to find max KE
  eg.
  spoon has mass of 200g and falls off a table 1m high, what is its max KE?
  a) calculate GPE
  GPE = m x g x h
  ? = 200 x 9.8 x 1
  max GPE = 1960
  b) total energy input = total energy output
  both equal the same
  max KE = 1960 J