What is energyWhat is energy

Look around you. Look around you. Is anything moving? Is anything moving? 

Can you hear, see or feel anything? Can you hear, see or feel anything? Sure... this is because something is making Sure... this is because something is making

something happen, and most probably, there something happen, and most probably, there is some power at work. This power or ability to is some power at work. This power or ability to make things happen is what we can call make things happen is what we can call energy. It makes things happen. It makes energy. It makes things happen. It makes change possible.change possible.                                                  

HEAT (Thermal energy)HEAT (Thermal energy) Thermal energy is what we call energy Thermal energy is what we call energy

that comes from heat. that comes from heat. For example, For example, a cup of hot tea has thermal energy in the a cup of hot tea has thermal energy in the

form of kinetic energy from its particles. form of kinetic energy from its particles. When you pour some milk into your tea, When you pour some milk into your tea,

some of this energy is transferred to the some of this energy is transferred to the particles in cold milk. What happens next? particles in cold milk. What happens next? The cup of tea is cooler because it lost The cup of tea is cooler because it lost thermal energy to the milk.thermal energy to the milk.

TemparatureTemparature

The temperature of an object is to do The temperature of an object is to do with how hot or cold it is, measured in with how hot or cold it is, measured in degrees Celsius (°C). A thermometer is degrees Celsius (°C). A thermometer is used to measure the temperature of an used to measure the temperature of an object.object. two examplestwo examples

1.1. A swimming pool at 30°C is at a lower temperature than a A swimming pool at 30°C is at a lower temperature than a cup of tea at 80°C. But the swimming pool contains more cup of tea at 80°C. But the swimming pool contains more water, so it stores more thermal energy than the cup of tea. water, so it stores more thermal energy than the cup of tea.

2.2. To boil water we must increase its temperature to 100°C. It To boil water we must increase its temperature to 100°C. It takes longer to boil a large beaker of water than a small takes longer to boil a large beaker of water than a small beaker because the large beaker contains more water and beaker because the large beaker contains more water and needs more thermal energy to reach 100°C needs more thermal energy to reach 100°C

the term energy describes the capacity to the term energy describes the capacity to produce changes within a system, without produce changes within a system, without regard to limitations in transformation regard to limitations in transformation imposed by entropy. imposed by entropy.

Changes in total energy of systems can only Changes in total energy of systems can only be accomplished by adding or subtracting be accomplished by adding or subtracting energy from them, as energy is a quantity energy from them, as energy is a quantity which is conserved, according to the first law which is conserved, according to the first law of thermodynamics.of thermodynamics.

According to special relativity, changes in the According to special relativity, changes in the energy of systems will also coincide with energy of systems will also coincide with changes in the system's mass, and the total changes in the system's mass, and the total amount of mass of a system is a measure of amount of mass of a system is a measure of its energy its energy

EnergyEnergy in a system may be  in a system may be transformedtransformedso so

that it resides in a different state.that it resides in a different state. Energy in many states may be used to do Energy in many states may be used to do

many varieties of physical work.many varieties of physical work. Energy may be used in natural processes or Energy may be used in natural processes or

machines, or else to provide some service to machines, or else to provide some service to society (such as heat, light, or motion).society (such as heat, light, or motion).

For example, an internal combustion engine For example, an internal combustion engine converts the potential chemical energy in converts the potential chemical energy in gasoline and oxygen into heat, which is then gasoline and oxygen into heat, which is then transformed into the propulsive energy transformed into the propulsive energy (kinetic energy that moves a vehicle.) A (kinetic energy that moves a vehicle.) A solar cell converts solar radiation into solar cell converts solar radiation into electrical energy that can then be used to electrical energy that can then be used to light a bulb or power a computer. light a bulb or power a computer.

In general, most types of energy, save for In general, most types of energy, save for thermal energy, may be converted to any thermal energy, may be converted to any other kind of energy, with a theoretical other kind of energy, with a theoretical efficiency of 100%. efficiency of 100%.

Such efficiencies might occur in practice, such Such efficiencies might occur in practice, such as when chemical potential energy is as when chemical potential energy is completely converted into kinetic energies, completely converted into kinetic energies, and vice versa, only in isolated systems.and vice versa, only in isolated systems.

Conversion of other types of energies to heat Conversion of other types of energies to heat also may occur with high efficiency but a also may occur with high efficiency but a perfect level would be only possible for perfect level would be only possible for isolated systems also. isolated systems also.

If there is nothing beyond the frontiers of the If there is nothing beyond the frontiers of the universe then the only real isolated system universe then the only real isolated system would be the universe it self. would be the universe it self.

Currently we do not have the knowledge or Currently we do not have the knowledge or technology to create an isolated system from technology to create an isolated system from a portion of the universe.a portion of the universe.

Exceptions for perfect efficiency (even for Exceptions for perfect efficiency (even for isolated systems) occur when energy has isolated systems) occur when energy has already been partly distributed among many already been partly distributed among many available quantum states for a collection of available quantum states for a collection of particles, which are freely allowed to explore particles, which are freely allowed to explore any state of momentum and position (phase any state of momentum and position (phase space).space).

In such circumstances, a measure called In such circumstances, a measure called entropy, or evening-out of energy distribution entropy, or evening-out of energy distribution in such states, dictates that future states of in such states, dictates that future states of the system must be of at least equal the system must be of at least equal evenness in energy distributionevenness in energy distribution. .

Trasfering HeatTrasfering Heat

1.condution1.condution

When a substance is heated, its When a substance is heated, its particles gain energy and vibrate more particles gain energy and vibrate more vigorously.vigorously.

The particles bump into nearby The particles bump into nearby particles and make them vibrate more. particles and make them vibrate more.

The particles pass the thermal energy The particles pass the thermal energy through the substance by conduction, through the substance by conduction, from the hot end to the cold end. from the hot end to the cold end.

Substances that allow thermal energy to Substances that allow thermal energy to move easily through them are called move easily through them are called conductors.conductors.  

Metals are good conductors of thermal Metals are good conductors of thermal energy. Substances that do not allow energy. Substances that do not allow thermal energy to move through them thermal energy to move through them easily are called easily are called insulatorsinsulators. Air and . Air and plastics are insulators.plastics are insulators.

ConvectionConvection

When particles in liquids and gases When particles in liquids and gases get warm, they become less dense, get warm, they become less dense, and they rise. and they rise.

The space is quickly replaced by The space is quickly replaced by cooler particles that are less dense cooler particles that are less dense (because they are heavier). (because they are heavier).

Thermal energy is transferred from Thermal energy is transferred from hot places to cold places (air or hot places to cold places (air or liquid) by convection.liquid) by convection.

Some examplesSome examples

Radiation Radiation All objects transfer thermal energy All objects transfer thermal energy

by infrared radiation.by infrared radiation. The hotter an object is, the more infrared The hotter an object is, the more infrared

radiation it gives off. radiation it gives off. No particles are involved in radiation, No particles are involved in radiation,

unlike conduction and convection. unlike conduction and convection. This means that thermal energy transfer This means that thermal energy transfer

by radiation can even work in space, but by radiation can even work in space, but conduction and convection cannot.conduction and convection cannot.

One good example is the sun. Even One good example is the sun. Even though it is millions of kilometers away though it is millions of kilometers away in space, we can still feel its heat. in space, we can still feel its heat. Radiation is how we can feel the heat Radiation is how we can feel the heat of the Sun.of the Sun.

Radiation Radiation

Solar panel Solar panel