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Thermal energy or Heat energy is related to the motion or vibration of molecules in a substance. When a thermal system changes, heat flows in or out of the system. Heat energy flows from hot bodies to cold ones. Heat flow, like work, is an energy transfer. When heat flows into a substance it may increase the kinetic energy of the particles and thus elevate its temperature. Heat flow may also change the arrangement of the particles making up a substance by increasing their potential energy. This is what happens to water when it reaches a temperature of 100ºC. The molecules of water move further away from each other, thereby changing the state of the water from a liquid to a gas. During the phase transition the temperature of the water does not change.


Nuclear Energy is energy that comes from the binding of the protons and neutrons that make up the nucleus of the atoms. It can be released from atoms in two different ways: nuclear fusion or nuclear fission. In nuclear fusion , energy is released when atoms are combined or fused together. This is how the sun produces energy. In nuclear fission , energy is released when atoms are split apart. Nuclear fission is used in nuclear power plants to produce electricity. Uranium 235 is the fuel used in most nuclear power plants because it undergoes a chain reaction extremely rapidly, resulting in the fission of trillions of atoms within a fraction of a second.


Sources and sinks

The source of energy for many processes occurring on the earth's surface comes from the sun. Radiating solar energy heats the earth unevenly, creating air movements in the atmosphere. Therefore, the sun drives the winds, ocean currents and the water cycle. Sunlight energy is used by plants to create chemical energy through a process called photosynthesis, and this supports the life and growth of plants. In addition, dead plant material decays, and over millions of years is converted into fossil fuels (oil, coal, etc.).

Today, we make use of various sources of energy found on earth to produce electricity. Using machines, we convert the energies of wind, biomass, fossil fuels, water, heat trapped in the earth (geothermal), nuclear and solar energy into usable electricity. The above sources of energy differ in amount, availability, time required for their formation and usefulness. For example, the energy released by one gram of uranium during nuclear fission is much larger than that produced during the combustion of an equal mass of coal.


(Source: US DOE) 1975 2000
Coal 14.989 (24.4%) 22.663 (31.5%)
Natural Gas (dry) 19.640 (32.0%) 19.741 (27.5%)
Crude Oil 17.729 (28.9%) 12.383 (17.2%)
Nuclear 1.900 (3.1%)  8.009 (11.2%)
Hydroelectric 3.155 (5.1%) 2.841 (4.0%)
Natural Gas (plant liquid) 2.374 (3.9%) 2.607 (3.6%)
Geothermal 0.070 (0.1%) 0.319 (0.4%)
Other 1.499 (2.5%) 3.275 (4.6%)
TOTAL 61.356 71.838


(Source: US Department of Energy)

An energy sink is anything that collects a significant quantity of energy that is either lost or not considered transferable in the system under study. Sources and sinks have to be included in an energy budget when accounting for the energy flowing into and out of a system.

Conservation of energy

Though energy can be converted from one form to another, energy cannot be created or destroyed. This principle is called the "law of conservation of energy." For example, in a motorcycle, the chemical potential energy of the fuel changes to kinetic energy. In a radio, electricity is converted into kinetic energy and wave energy (sound).

Machines can be used to convert energy from one form to another. Though ideal machines conserve the mechanical energy of a system, some of the energy always turns into heat when using a machine. For example, heat generated by friction is hard to collect and transform into another form of energy. In this situation, heat energy is usually considered unusable or lost.


Energy units

In the International System of Units (SI), the unit of work or energy is the Joule (J). For very small amounts of energy, the erg (erg) is sometimes used. An erg is one ten millionth of a Joule: 

1 Joule = 10 , 000 , 000 ergs size 12{ matrix { 1 {} # ital "Joule"{}} = matrix { "10","000","000" {} # ital "ergs"{}} } {}

Power is the rate at which energy is used. The unit of power is the Watt (W), named after James Watt, who perfected the steam engine:

1 Watt = 1 Joule /sec ond size 12{ matrix { 1 {} # ital "Watt"{}} = matrix { 1 {} # ital "Joule""/sec" ital "ond"{}} } {}

 Power is sometimes measured in horsepower (hp):

1 horsepower = 746 Watts size 12{ matrix { 1 {} # ital "horsepower"{}} = matrix { "746" {} # ital "Watts"{}} } {}

  Electrical ene rgy is generally expressed in kilowatt-hours (kWh):

1 kilowatt hour = 3, 600 , 000 Joules size 12{ matrix { 1 {} # ital "kilowatt" - ital "hour"{}} = matrix { 3,"600","000" {} # ital "Joules"{}} } {}

It is important to realize that a kilowatt-hour is a unit of energy not power. For example, an iron rated at 2000 Watts size 12{ matrix { "2000" {} # ital "Watts"{}} } {} would consume 2x3 . 6x 10 6 J size 12{ matrix { 2x3 "." 6x"10" rSup { size 8{6} } {} # J{}} } {} of energy in 1 hour size 12{ matrix { 1 {} # ital "hour"{}} } {} .

Heat energy is often measured in calories. One calorie (cal) is defined as the heat required to raise the temperature of 1 gram size 12{ matrix { 1 {} # ital "gram"{}} } {} of water from 14.5 to 15.5 ºC:

1 calorie = 4 . 189 Joules size 12{ matrix { 1 {} # ital "calorie"{}} = matrix { 4 "." "189" {} # ital "Joules"{}} } {}

An old, but still used unit of heat is the British Thermal Unit (BTU). It is defined as the heat energy required to raise the energy temperature of 1 pound of water from 63 size 12{"63"} {} to 64 ° F size 12{"64""" lSup { size 8{ circ } } F} {} .

 Physical Quantity Name Symbol SI Unit
  Force Newton N kg m / s 2 size 12{ ital "kg" cdot m/s rSup { size 8{2} } } {}
  Energy Joule J kg m 2 / s 2 size 12{ ital "kg" cdot m rSup { size 8{2} } /s rSup { size 8{2} } } {}
  Power  Watt W kg m 2 / s 3 size 12{ ital "kg" cdot m rSup { size 8{2} } /s rSup { size 8{3} } } {}

  1 BTU = 1055 Joules size 12{ matrix { 1 {} # ital "BTU"{}} = matrix { "1055" {} # ital "Joules"{}} } {}

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Ap environmental science. OpenStax CNX. Sep 25, 2009 Download for free at http://cnx.org/content/col10548/1.2
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