morsy
26 - 12 - 08, 02:31 PM
Despite all my nit-picking in the words above, most scientists and engineers find it acceptable and useful to talk about chemical and electrical and mechanical and magnetic energy and others. They also frequently describe internal energy as heat or "heat content" or "quantity of heat" as some of the older texts call it.
But it is helpful to understand why some people say that all those other forms of energy are really types of kinetic energy or potential energy being "expressed" in different ways.
Electrical energy, for example, is the flow of charged particles called electrons or ions. When electrons are flowing through a wire or through hundreds of feet of air (an event we call lightning) it is because they are being "pushed" or forced by an electrical field. This field is caused by a difference in electrical charge. A force is exerted on the electrons and they move. Work is done on the charged particles. A force is pushing them through a distance. Actually, they are hopping from atom to atom, being pushed by an electromotive force. While the electrons are moving they contain kinetic energy. So at the itsy-bitsy atomic level electricity is a form of kinetic energy.
Mechanical energy is the useful way we sometimes refer to things like gears, engines, locomotives pulling trains, canon balls flying through the air, or other examples of energy in mechanical devices. But, of course, by now you see that all these moving parts contain kinetic energy. They are really just different modes of kinetic energy - the energy contained in a moving mass. In order to get these various objects spinning or rolling, a force has to be exerted. Work is a force acting through a distance, so the way they get moving and keep moving is by having work done on them. Work is an energy transfer process.
Chemical energy is another term we use a lot. This is more vague. We say things like, "during combustion, chemical energy is released". Hmmm. The term chemical energy refers to energy that is stored in molecular bonds, the forces that hold molecules together. So releasing chemical energy must mean the energy is finally free from its molecular bonds. In the more general sense, of course, it is potential energy. Stored energy, or energy that is "waiting to happen", or that has the "potential" to happen, or that can happen but hasn't yet, is rather sensibly called potential energy.
As described in the photosynthesis section, carbohydrate molecules, used by living organisms for food (and other things), store energy in their atomic bonds. Living cells release this stored energy relatively slowly by a process called respiration. Some of the stored potential energy becomes the kinetic energy of cell processes and muscle movement and some of it becomes internal energy (often called heat). But now you know I should have said, "some of stored energy is transferred by the heat process into the internal energy of the cell. The cell is "warmed up" by increasing the average energy of the cell molecules. Eventually, of course, all of it becomes internal energy and then flows by heat transfer into the air and objects around the organism.
Enough examples. We get the idea. Maybe you can think about some other forms. Unless you are writing a thermodynamics text book it is probably okay to say there are more than two forms of energy and to use the terms heat and work as if they are a type of energy. So when you find me doing it in this web site, don't write me a nit-picky e-mail telling me heat is a process, not a form of energy. I know. I know.
Thermal Energy (side note added later)
Bopping around in various text books and resources is the fairly common term "thermal energy". This seems generally to be used as another term for internal energy or heat content. One of my thermo books does outright propose this term as a way to avoid using heat as a type of energy. According to this book, it was tried in the past but never quite caught on. I still like the idea, and so have started using the term interchangeably in new pages on this site. So in this web site when you see the term thermal energy it means the type of internal energy that is usually called heat as described above. It the short run it may add to your confusion, but in the long run you'll be the wiser for it. Do you buy that?
Back to where you where (if you came from above)
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Thermal Energy is Total Kinetic Energy
by ismail morsy (revised10 noveber2008)
The thermal energy of an object consists of the total kinetic energy of all its atoms and molecules. It is a form of energy related to heat and temperature. Thermal energy can be created internally with chemical, nuclear and electrical reactions. It can also be created or increased from external effects, such as mechanical motion, radiation and thermal conduction.
Questions you may have include:
How can thermal energy be created?
What are internal reactions?
What are external effects?
Creation of thermal energy
Thermal energy is the total internal kinetic energy of an object due to the random motion of its atoms and molecules. It is sometimes confused with internal energy or thermodynamic energy. They consist of the sum of the internal kinetic energy (thermal energy) and the potential energy of an object. You may need to make sure which definition a teacher or book is using.
Kinetic Theory of Matter
The Kinetic Theory of Matter states that matter consists of atoms or molecules in random motion. Those moving particles can transfer their kinetic energy to other nearby particles. The total kinetic energy of all the particles in an object make up the thermal energy of that object.
Temperature and heat
Temperature and heat are related to thermal energy.
Temperature is defined as the average kinetic energy of all the atoms or molecules in an object.
Heat is defined as the flow of thermal energy from an object of one temperature to an object of another temperature. You feel the flow of heat when warm air from a furnace reaches you.
Internal reactions
The thermal energy of an object can be created or increased by chemical and nuclear reactions, as well as electrical effects. Each releases or transfers energy that cause an object's internal particles to increase their motion and thus their kinetic energy.
Chemical
For example, some chemical reactions cause nearby molecules to accelerate, thus increasing the total thermal energy of the object. Burning is a common form of a heat-producing chemical reaction.
Nuclear
Nuclear reactions, such as nuclear fission or nuclear decay, give off high-speed particles that increase the thermal energy of a material.
Electrical resistance
The resistance to the motion of electrons in an electrical circuit cause the wire's molecules to increase their kinetic motion, thus increasing the thermal energy of the wire. Often you can feel the wire get warm when electricity is flowing through it.
External effects
External sources of energy such as mechanical motion, radiation and thermal conduction can also increase the thermal energy of an object.
Mechanical
Mechanical sources of heat are primarily external. When objects rub together, the friction causes molecules to increase their energy, resulting in heat. Likewise, bending or pounding on a piece of metal will cause it to get warmer.
Radiation
Light from the sun radiating on an object can transfer energy to the object's molecules, causing them to move faster. In other words, the object heats up. Radiation is considered a form of heat transfer.
Conduction of heat
The Kinetic Theory of Matter shows how the kinetic energy of a material's particles can be increased though collisions with faster nearby particles. This explains how a material can be heated through conduction heat transfer.
Summary
Thermal energy consists of the total internal kinetic energy of an object due to the random motion of its atoms and molecules. It is related to heat and temperature. Thermal energy can be created internally with chemical, nuclear and electrical reactions. It can also be created or increased from external effects, such as mechanical, radiation and conduction effects.
But it is helpful to understand why some people say that all those other forms of energy are really types of kinetic energy or potential energy being "expressed" in different ways.
Electrical energy, for example, is the flow of charged particles called electrons or ions. When electrons are flowing through a wire or through hundreds of feet of air (an event we call lightning) it is because they are being "pushed" or forced by an electrical field. This field is caused by a difference in electrical charge. A force is exerted on the electrons and they move. Work is done on the charged particles. A force is pushing them through a distance. Actually, they are hopping from atom to atom, being pushed by an electromotive force. While the electrons are moving they contain kinetic energy. So at the itsy-bitsy atomic level electricity is a form of kinetic energy.
Mechanical energy is the useful way we sometimes refer to things like gears, engines, locomotives pulling trains, canon balls flying through the air, or other examples of energy in mechanical devices. But, of course, by now you see that all these moving parts contain kinetic energy. They are really just different modes of kinetic energy - the energy contained in a moving mass. In order to get these various objects spinning or rolling, a force has to be exerted. Work is a force acting through a distance, so the way they get moving and keep moving is by having work done on them. Work is an energy transfer process.
Chemical energy is another term we use a lot. This is more vague. We say things like, "during combustion, chemical energy is released". Hmmm. The term chemical energy refers to energy that is stored in molecular bonds, the forces that hold molecules together. So releasing chemical energy must mean the energy is finally free from its molecular bonds. In the more general sense, of course, it is potential energy. Stored energy, or energy that is "waiting to happen", or that has the "potential" to happen, or that can happen but hasn't yet, is rather sensibly called potential energy.
As described in the photosynthesis section, carbohydrate molecules, used by living organisms for food (and other things), store energy in their atomic bonds. Living cells release this stored energy relatively slowly by a process called respiration. Some of the stored potential energy becomes the kinetic energy of cell processes and muscle movement and some of it becomes internal energy (often called heat). But now you know I should have said, "some of stored energy is transferred by the heat process into the internal energy of the cell. The cell is "warmed up" by increasing the average energy of the cell molecules. Eventually, of course, all of it becomes internal energy and then flows by heat transfer into the air and objects around the organism.
Enough examples. We get the idea. Maybe you can think about some other forms. Unless you are writing a thermodynamics text book it is probably okay to say there are more than two forms of energy and to use the terms heat and work as if they are a type of energy. So when you find me doing it in this web site, don't write me a nit-picky e-mail telling me heat is a process, not a form of energy. I know. I know.
Thermal Energy (side note added later)
Bopping around in various text books and resources is the fairly common term "thermal energy". This seems generally to be used as another term for internal energy or heat content. One of my thermo books does outright propose this term as a way to avoid using heat as a type of energy. According to this book, it was tried in the past but never quite caught on. I still like the idea, and so have started using the term interchangeably in new pages on this site. So in this web site when you see the term thermal energy it means the type of internal energy that is usually called heat as described above. It the short run it may add to your confusion, but in the long run you'll be the wiser for it. Do you buy that?
Back to where you where (if you came from above)
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Thermal Energy is Total Kinetic Energy
by ismail morsy (revised10 noveber2008)
The thermal energy of an object consists of the total kinetic energy of all its atoms and molecules. It is a form of energy related to heat and temperature. Thermal energy can be created internally with chemical, nuclear and electrical reactions. It can also be created or increased from external effects, such as mechanical motion, radiation and thermal conduction.
Questions you may have include:
How can thermal energy be created?
What are internal reactions?
What are external effects?
Creation of thermal energy
Thermal energy is the total internal kinetic energy of an object due to the random motion of its atoms and molecules. It is sometimes confused with internal energy or thermodynamic energy. They consist of the sum of the internal kinetic energy (thermal energy) and the potential energy of an object. You may need to make sure which definition a teacher or book is using.
Kinetic Theory of Matter
The Kinetic Theory of Matter states that matter consists of atoms or molecules in random motion. Those moving particles can transfer their kinetic energy to other nearby particles. The total kinetic energy of all the particles in an object make up the thermal energy of that object.
Temperature and heat
Temperature and heat are related to thermal energy.
Temperature is defined as the average kinetic energy of all the atoms or molecules in an object.
Heat is defined as the flow of thermal energy from an object of one temperature to an object of another temperature. You feel the flow of heat when warm air from a furnace reaches you.
Internal reactions
The thermal energy of an object can be created or increased by chemical and nuclear reactions, as well as electrical effects. Each releases or transfers energy that cause an object's internal particles to increase their motion and thus their kinetic energy.
Chemical
For example, some chemical reactions cause nearby molecules to accelerate, thus increasing the total thermal energy of the object. Burning is a common form of a heat-producing chemical reaction.
Nuclear
Nuclear reactions, such as nuclear fission or nuclear decay, give off high-speed particles that increase the thermal energy of a material.
Electrical resistance
The resistance to the motion of electrons in an electrical circuit cause the wire's molecules to increase their kinetic motion, thus increasing the thermal energy of the wire. Often you can feel the wire get warm when electricity is flowing through it.
External effects
External sources of energy such as mechanical motion, radiation and thermal conduction can also increase the thermal energy of an object.
Mechanical
Mechanical sources of heat are primarily external. When objects rub together, the friction causes molecules to increase their energy, resulting in heat. Likewise, bending or pounding on a piece of metal will cause it to get warmer.
Radiation
Light from the sun radiating on an object can transfer energy to the object's molecules, causing them to move faster. In other words, the object heats up. Radiation is considered a form of heat transfer.
Conduction of heat
The Kinetic Theory of Matter shows how the kinetic energy of a material's particles can be increased though collisions with faster nearby particles. This explains how a material can be heated through conduction heat transfer.
Summary
Thermal energy consists of the total internal kinetic energy of an object due to the random motion of its atoms and molecules. It is related to heat and temperature. Thermal energy can be created internally with chemical, nuclear and electrical reactions. It can also be created or increased from external effects, such as mechanical, radiation and conduction effects.