Energy stores and transfers

Question 1

system

Answer 1

an object or group of objects

Question 2

what happens whenever anything changes in a system?

Answer 2

whenever anything changes in a system, energy is transferred between its stores or surroundings.

Question 3

closed system

Answer 3

a closed system is where no energy can escape to or enter from the surroundings. The total energy in a closed system never changes.

Question 4

kinetic energy store store

Answer 4

the energy an object has because of its motion

Question 5

gravitational potential energy store

Answer 5

the energy an object has due to its elevating height in a gravitational field

Question 6

elastic potential energy store

Answer 6

the energy an object has when it’s being stretched or compressed.

Question 7

how many energy stores are there?

Answer 7

8

Question 8

thermal/internal energy store

Answer 8

the energy an object has because of its temperature (sum of kinetic and potential energy)

Question 9

chemical energy store

Answer 9

the energy stored in chemical bonds, energy can be transferred by chemical reactions involving food, fuel, and batteries.

Question 10

nuclear energy store

Answer 10

energy stored in the nucleus of an atom

Question 11

magnetic energy store

Answer 11

energy a magnetic object has when it is near a magnet or in a magnetic field.

Question 12

electrostatic energy store

Answer 12

energy a charged object has when near another charged object

Question 13

how many energy transfers are there?

Answer 13

4

Question 14

list the 4 energy transfers/ pathways and a brief summary of each.

Answer 14

HEATING = energy transferred to an object with a lower temperature
RADIATION = waves (light and sound)
ELECTRICITY = when an electric current flows
MECHANICAL = by force

Question 15

describe the energy transfers when stretching a rubber band

Answer 15

when you stretch a rubber band, energy from your chemical store is mechanically transferred to the elastic potential energy store of the rubber band.

Question 16

describe the energy transfers when a block is dropped from a height

Answer 16

when a block is dropped from a height. energy is mechanically transferred (by gravity) from the gravitational potential energy store of the block to kinetic energy store.

Question 17

describe the energy transfers when the block hits the ground.

Answer 17

when this block hits the ground, energy from the kinetic energy store is transferred mechanically and by radiation (sound waves) to thermal energy store of the surrounding.

Question 18

describe the energy transfers in a kettle heating up water

Answer 18

the electric current in the kettle transfers energy to the heating element’s thermal energy store. Energy is transferred by heating to the thermal energy store of the water.

Question 19

describe the energy transfers when an object slows down due to friction

Answer 19

when an object slows down due to friction, energy is transferred from the object’s kinetic energy store to its thermal store, the thermal store of the object it is rubbing against, and to the surroundings

Question 20

whats the equation for gravitational potential energy?

Answer 20

Ep = mgh

Ep = gravitational potential energy (J)
m = mass (kg)
g = gravitational field strength (N/kg)
h = height (m)

Question 21

whats the equation for kinetic energy?

Answer 21

Ek = ½mv²

Ek = kinetic energy (J)
m = mass (kg)
v = speed (m/s)

Question 22

power

Answer 22

how much work is done/how much energy is transferred per second.

Question 23

what is work done?

Answer 23

work done means the same thing as energy transferred.

Question 24

whats the equation of power involving energy transferred?

Answer 24

P = E/t

P = power (W)
E = energy transferred (J)
t = time (s)

Question 25

whats the equation of power involving work done?

Answer 25

P = W/t P = power (W) W = work done (J) t = time (s)

Question 26

1 watt = ?

Answer 26

1 W = 1 J of energy transferred per second

Question 27

whats the equation for elastic potential energy?

Answer 27

Ee =½ke² Ee = elastic potential energy (J) k = spring constant (N/m) e = extension (m)

Question 28

law of conservation of energy

Answer 28

energy cannot be created nor destroyed, it can only be transferred from one store to another.

Question 29

other than TRANSFERRING energy, what else can happen?

Answer 29

energy can only be transferred usefully, stored, or dissipated (wasted)

Question 30

dissipated energy

Answer 30

dissipated energy is often described as being wasted

Question 31

where does energy actually go?

Answer 31

energy is never entirely transferred usefully - some energy is always dissipated, meaning it is transferred to less useful stores

Question 32

where does all energy eventually end up at?

Answer 32

all energy eventually ends up being transferred to the thermal energy store of the surroundings

Question 33

Lubrication

Answer 33

a way of reducing unwanted energy transfer due to friction, rather, allowing smooth movement.

Question 34

Streamlining

Answer 34

a way of reducing energy wasted due to air resistance or drag in water.

Question 35

what is efficiency a measure of?

Answer 35

efficiency is a measure of how much energy is transferred usefully.

Question 36

whats the equation for effficiency? (energy)

Answer 36

efficiency = useful output energy transfer (J) / total input energy transfer (J)

Question 37

whats the equation for efficiency? (power)

Answer 37

efficiency = useful power output (W) / total power input (W)

Question 38

How is energy wasted in machines due to the work done against the force of friction?

Answer 38

in machines, work done against the force of friction usually causes energy to be wasted because energy is transferred to the thermal store of the machine and its surroundings.

Question 39

name an example of a way to reduce energy wasted due to heat dissipated to the surroundings.

Answer 39

thermal insulation is a way of reducing energy wasted to to heat dissipated to the surroundings.