Energy Flashcards
1
Q
What is kinetic energy
A
kinetic energy is the energy stored in moving objects
2
Q
do stationary objects have kinetic energy
A
no stationary objects such as a parked car do not have kinetic energy
3
Q
what is the formula for kinetic energy
A
Ek=1/2mv^2
4
Q
what are the units for kinetic energy, mass, velocity
A
energy transferred= Joules
Mass=kg
velocity=m/s
5
Q
car runs on petrol- store of chemical energy
A
a chemical reaction takes place in the engine and some of the energy is converted to kinetic energy store as the car moves
6
Q
A car with a mass of 700kg is moving with a speed of 20m/s . calculate the kinetic energy of the car
A
Ek=1/2mv^2
1/2x700x20^2= 140,000J
140KJ
7
Q
A cyclist and bike have a total mass of 100kg and a speed of 15m/s. Calculate the kinetic energy.
A
Ek=1/2mv^2
1/2x100x15^2= 11250J
11.25KJ
8
Q
A tennis ball is travelling at 50m/s and has a kinetic energy of 75J. calculate the mass of the tennis ball.
A
Ek=1/2mv^2
75J=1/2m50^2
75J=1250m
75 divided by 1250=0.06kg
9
Q
what is elastic potential energy
A
when we stretch a spring we are applying a force to change the length of the spring. we are putting energy in to stretch the spring and the stretched spring stores this energy. the energy that the stretched spring stores is called elastic potential energy.
10
Q
if we apply a force, the spring will stretch, what do we call this stretch
A
the extension (e) the extension is directly proportional to the force up until the limit of proportionality.
11
Q
what is the formula for elastic potential energy
A
Ee=1/2ke^2 energy=J spring constant=N/m e=metres value of spring constant depends on the spring.
12
Q
A spring has an extension of 20cm.Calculate the elastic potential energy stored in a spring k=100n/m
A
Ee=1/2ke^2
1/2x100x0.02m^2
2J
13
Q
What is gravitational potential energy?
A
-the energy stored in an object due to its position above the Earth’s surface
it is due to the force of gravity acting on the object
14
Q
lifting ball off ground example
A
a ball is sitting on a shelf, pete lifts the ball off the ground and puts it on a shelf. the chemical energy store in Pete’s muscles is being converted into gravitational potential energy in the ball. so the ball now has a store of gravitational potential energy. if the ball rolls off the shelf, the gravitational potential energy is changed to other forms of energy such as kinetic energy or thermal energy so the ball now has no gravitational potential energy.
15
Q
what is the formula for gravitational potential energy
A
Ep=mgh mass=kg g=n/kg h=m Ep=Joules what is the gravitational field strength- measure of force of gravity
16
Q
A crane lifts a 75kg mass from a height of 8m.Calculate the gravitational potential energy gained by the mass. g=9.8N/kg
A
Ep=mgh
75x9.8x8= 5880J
17
Q
A ball with a mass of 500g is lifted onto a shelf which is 1.5m above the ground.calculate the gravitational potential energy gained by the ball. g=9.8N/kg
A
Ep=mgh
0.5kgx9.8x1.5= 7..35J
18
Q
What is specific heat capacity?
A
the specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg of the substance by 1 degree celsius.
19
Q
calculate energy required to increase the temperature of 2kg of water from 20 degrees celsius to 100 degrees celsius. the specific heat capacity of water is 4200j/kg
A
change in thermal energy= mxc change in temperature
mass x specific heat capacity x change in temperature
2x4200x80=672000J
672Kj
20
Q
An iron has an aluminium plate with a mass of 1.5 kg. calculate the thermal energy stored in the plate when the temperature rises from 20 degrees to 200 degrees. the specific heat capacity of aluminum is 913 j/kg
A
change in thermal energy= mass x specific heat capacity x change in temperature
- 5 x 913 x 180= 246510J
- 51KJ
21
Q
A hot water bottle cools down from 80 degrees celsius to 20 degrees celsius releasing 756000J of thermal energy. Calculate the mass of the water in the hot water bottle. c=4200j/kg
A
change in thermal energy= mass x specific heat capacity x change in temperature 756000=massx4200x60 756000=252000m m=3 3kg
22
Q
recap of different energy stores, kinetic energy, gravitational potential energy, elastic potential energy
A
kinetic energy: energy stored in moving objects
gravitational potential energy: energy stored due to an object’s position above the Earth’s surface. It is due to the force of gravity acting on an object
Elastic potential energy: elastic potential energy is the energy stored in a stretched spring
thermal energy: energy stored due to object’s temperature
23
Q
The law of conservation of energy:
A
Energy can be transferred fully, stored or disspated but cannot be created or destroyed.
24
Q
What is a system
A
a system is an object or a group of objects
25
a pendulum setup
a fixed point, string and a mass
26
what is a closed system
in a closed system no energy or matter can enter or leave
27
pendulum energy transfers
at the top the mass has the maximum store of gravitational potential energy. as the pendulum swings, this is transferred to the kinetic energy store. the mass has the maximum kinetic energy store at the bottom of the spring. why does the mass have the maximum kinetic energy store at the bottom- because thats where its moving at the fastest speed. as the mass swings back up, the kinetic energy store is transferred into the gravitational potential energy store again.
28
what is the problem with the pendulum model
friction has not been considered. as the pendulum swings there is friction in the fixed point. there is also friction as the pendulum passes through air particles. friction causes energy to be transferred to thermal energy stores. the fixed point and the air around the pendulum gradually get warmer. these stores of thermal energy are less useful- energy has been dissipated. this causes pendulum to gradually swing with less energy and it will eventually stop
29
how can we reduce unwanted energy transfers?
-reduce friction by using lubricants on moving parts. in the case of the pendulum we could use oil around the fixed point to reduce friction around it. or we could also remove the air particles from around the pendulum
30
Energy transfers- bungee jumping
at the start of the jump all of the energy in the system is the store of gravitational potential energy. As the jumper falls, energy is transferred from the gravitational potential energy store to the kinetic energy store. when the bungee rope starts to tighten, the kinetic energy store is now at its maximum. when the rope is fully extended the kinetic energy store is zero because the jumper is not moving. at this point, all of the energy has been transferred to the elastic potential energy store. when the bungee jump recoils, energy is transferred from the elastic potential energy store back to the kinetic energy store. during the ascent, energy is transferred from the kinetic energy store back to the gravitational potential energy store. at the top of the ascent all of the energy is now in the gravitational potential energy store.
31
why does the jumper never return to their original position
jumper never returns back to original position because energy is dissipated as thermal energy this is due to friction with air particles as jumper swings through the air. also due to stretching effects in the bungee rope which is not fully elastic. bungee ropes are not fully elastic which is why some thermal energy is always dissipated during stretching and recoil.
32
Work done by force what is the definition
-work is done when energy is transferred from one store to another
33
what is mechanical work
mechanical work is when a force is used to move an object
34
what is electrical work
electrical work is involves a current transferring energy
35
a dog moving a sledge. energy transfers
the chemical energy store of the dog is being transferred to the kinetic energy store of the moving sledge. force of friction is acting between sledge and ground so some of the energy from the kinetic energy store is being transferred to the thermal energy store in the sledge and the ground.
36
work done formula
work done (joules)= force (newtons) x distance (metres)
37
car example energy transfer from kinetic energy store of moving car to thermal energy store of the brakes
a car is travelling at a speed of 20m/s. the driver applies the brakes and the car stops. a moving car has a kinetic energy store. when the driver presses on the brakes, the brakes press against the wheel. this creates friction between the wheel and the brakes. energy from the kinetic energy store is transferred to the thermal energy store of the brakes so the temperature of the brakes increases and the car slows down and stops. so energy has been transferred from the kinetic energy store of the moving car to the thermal energy store of the brakes. so work has been done.
38
During braking, a force of 2000N is applied to the brakes of the car. the car takes 20m to come to a stop. calculate the work done.
work done (joules)= force( newtons) x distance (metres)
40000J
40KJ
39
What is the definition of power
power is the rate at which energy is transferred, or the rate at which work is done.
power (w)= energy (j)/ time (s)
power (w)= work done (j)/ time (s)
1 watt is work done of 1 J per second
40
when a car stops, 40000J of work is done by the brakes in a time of 5 seconds.calculate power of the brakes
power (w)= energy (J)/time (s)
40000/5 =8000 Watts
8000 Watts
41
Motor A transfers 500J of electrical energy into gravitational potential energy in 40 seconds.
Motor B transfers 500J of electrical energy into gravitational potential energy in 60 seconds.
motor A power (w)=energy (j) / time (s) 12.5 watts
| Motor B= 500/60 8.33 Watts
42
Efficiency
useful power output/ total power input
| useful energy output/ total energy input
43
An electrical hob is used to heat water. 15000 J of thermal energy is transferred by the hob. 12000J of thermal energy passes into the water. calculate the efficiency of the energy transfer into the water
12000/15000=0.8
| useful power output/ total energy input
44
An electric current delivers a power of 60 watts to a light bulb. 3 watts of electrical energy are transferred to light energy. calculate the efficieny of the bulb.
3/60 =0.05
| useful power output/ total power input
45
how to reduce heat loss from the hob
use a pan with a wider base and a lid to prevent thermal energy from dissipating from the surface of the water and the edges of the pan. reduce unwanted transfer of thermal energy
46
kettle why is it more efficient at heating water
kettle plastic walls and lid reduce thermal energy transfer because plastic is an insulator and poor conductor of heat. plastic has lower conductivity. the heating element is also inside the kettle unlike when using a pan alot of thermal energy is used to heat the pan itself.
47
Cooling of buildings factors that affect cooling of buildings
1) thermal conductivity- the higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material.
cavity wall insulation- builders pack cavity with insulating material which has very low thermal condictivty. air is a poor conductor so air is trapped in foam in a gap between innner wall and outer wall to reduce heat loss, much less thermal energy passes through the walls and escapes from the house.
48
double glazed windows
lower thermal conductivity so less thermal energy can pass through and leave the house interior. double glazing has a vacuum layer (no particles) to prevent both conduction and convection.
49
loft insulation
loft insulation stops convection currents from forming in the loft
low thermal conductivity reducing the rate at which thermal energy passes through.
50
how can we reduce thermal energy transfer from a house
by constructing the building using materials with low thermal conductivities.
building houses with thick walls as this also reduces the rate of thermal energy transfer.
51
Energy from fossil fuels - uses of energy are:
transport, heating and generating electricity
52
what are the three main fossil fuels:
coal
oil
gas
53
fossil fuels supply 80 percent of the world's total energy needs because they have a number of advantages:
- they are reliable they always provide energy when we need it
- fossil fuels release a great deal of energy
- they are abundant and relatively cheap
- they are extremely versatile they are portable
54
Disadvantages of using fossil fuels to meet energy needs:
- burning fossil fuels releases a huge amount of carbon dioxide and that has contributed to climate change.
- they are non renewable; they are not being replenished as we use them.
- burning fossil fuels can release other pollutants: burning diesel releases carbon particulates which cause global dimming and burning coal releases sulfur dioxide which leads to acid rain. acid rain damages buildings and trees.
55
Nuclear power- non renewable
nuclear power plants run on elements such as uranium and plotonium
56
advantages of nuclear power
- once nuclear power plants are up and running they do not release carbon dioxide. nucleur power does not contribute to climate change
- extremely reliable produces lots of electricity exactly when we want it
57
disadvantages of nucleur power plants
nuclear power plants contain highly radioactive dangerous materials. if there was an accident these materials could be released into the environment.
- decommissioning a nuclear power plant takes many years and is very expensive.
- during its life and during decommisioning, a nuclear power plant generates large amounts of highly dangerous radioactive waste. this must be stored for thousands of years before its safe.
58
UK Energy mix - what has the uk got abundant reserves of
-coal up until 1950s almost all electricity generated in the uk came from burning coal
-coal and coal gas used for almost all heating and cooking
nuclear power introduced 1980s it produced 20 percent of uks electricity
oil and gas production began to replace coal for electricity generation
59
benefits of switching from burning coal to gas
burning gas releases less carbon dioxide then burning coal. this contributes less to climate change.
-gas fired power stations are flexible they can be switched on very quickly during periods of high demand they have a short start up time
coal fired power stations on the other hand have a very long start up time
60
why did we switch to renewable sources of energy
by the 1970s scientists realised that carbon dioxide emissions from human activity could be leading to climate change. energy from fossil fuels was very cheap it was an economic factor switching away from fossil fuels costs money and that could cost jobs.
61
what was the kyoto protocol
countries committed to reducing greenhouse gas emissions.
62
how can we adress the reliability problems of using renewable sources of energy
we need a base load ( constant supply of electricity thats on all the time) nuclear power is ideal for this because nuclear power stations cannot easily be turned on and off they are left on all the time. nucleur power does not release any greenhouse gases.
-we can use gas fired power stations to provide emergency power in times of peak demand. start up time for gas fired power stations is very short. ( switched on quickly)
63
future: renewable nuclear and gas fired power stations
renewables will provide bulk for our electricity
nucleur provide baseload ( constant supply of electricity thats on all the time)
gas providing energy in times of peak demand
64
renewable source definition
```
a renewable energy resource is one that is being or can be replenished as it is used.
wind power,
solar power
hydroelectric power
tidal power
biofuels
geothermal
wave power
```
65
advantages of renewable resources of energy
- renewable energy resources will never run out
| - renewable resources of energy do not add carbon dioxide to the atmosphere. they do not contribute to climate change.
66
disadvantages of renewable resources of energy
wind power and solar power are not reliable. some days are simply not windy and solar power does not work well on cloudy days
hydroelectric power is very reliable but habitats are destroyed when dams are built and valleys are flooded.
hydroelectricity is only useful in countries with lots of rivers so its not really suitable for uk.
tidal power is extremely reliable currently, uk doesnt generate any electricity from tidal power tidal barriers could be a harmful to wildlife
67
what is geothermal energy
geothermal energy uses heat from the earth to generate electricity and heat buildings
68
what is biofuel
biofuel is produced from plant minerals biofuels are carbon neutral, burning them does not release extra co2 into the amosphere
they can be used for transport
however lands used for farming and habitats are used to make bio fuels.
69
required practical thermal insulators: how to investigate effectiveness of thermal insulators
1) first place a small beaker inside a large beaker.
2) use a kettle to boil some water.
3) next, transfer 80cm^3 of hot water into the small beaker
4) use a piece of cardboard as a lid for the large beaker, must have a hole for thermometer
5) place thermometer through hole in the lid
6) the bulb of the thermometer must be inside the hot water
7) record starting temperature of the water and start a stopwatch
8) record temperature of water every 3 minutes for 15 minutes
9) next repeat experiment using same volume of hot water however this time use an insulating material (bubble wrap, wool) to fill the gap between the two beakers.
10) test a range of different insulating materials for example polystyrene balls and cotton wool
11) use same mass of insulating material each time
70
what are the variables for this experiment
independent variable- different types of insulators
dependent variable- temperature decrease
control variable- volume of water and mass of insulating material
the starting temperature of the water must also be kept the same each experiment
71
analysis
water will cool down most slowly with the most effective insulating material
72
we can also investigate effect of thickness of each material, how?
start with a beaker containing 80cm^3 of hot water
measure temperature of water every three minutes for 15 minutes
repeat experiment but wrap two layers of newspaper around beaker
repeat two more times using four layers and then 6 layers of newspaper
73
what are the variables
independent variable- number of layers of newspaper
dependent variable- temperature decrease
control variables- starting temperature of water
volume of water
74
analysis
more layers of newspaper, the slower the water cools down because more layers is a more effective thermal insulator than fewer layers
75
what is conduction
conduction is the process where vibrating particles transfer energy to neighbouring particles
76
what is conduction
conduction is the process when vibrating particles transfer heat energy to neighbouring particles
77
what is thermal conductivity
thermal conductivity is the measure of how quickly energy is transferred through a material. materials with high thermal conductivity transfer energy between their particles quickly.
78
describe how energy is transferred through the walls of the can of the drink by conduction
- in a metal free electrons
- gain kinetic energy
- free electrons transfer energy to other electrons
- by collisions
79
the energy from the can of drink is transferred to the air around the can chiller. a convection current is set up around the can chiller explain how
what is convection firstly- convection is where energetic particles move away from hotter to cooler regions
- particles in the air are free to move they gain kinetic energy and move faster and the space between each particle increases, they spread apart so the density decreases this causes the warm air to rise.
- particles move faster
- particles spread out
- density decreases
- warm air rises
80
two features of the metal cooling fins that could help them transfer energy quickly to the surroundings
- large surface area
| - dark colour
81
the blades of a turbine are 20 meters long. on average 15000kg of air moving at a speed of 12m/s hits the blades every second calculate the kinetic energy of the air hitting the blades every second
kinetic energy formula= 1/2mv^2
| 1/2x15000x12m/s^2= 1,080,000J
