However complex the workings of living organisms, they share with all other natural systems the same physical principles of the conservation and transformation of matter and energy. Over long spans of time, matter and energy are transformed among living things, and between them and the physical environment. In these grand-scale cycles, the total amount of matter and energy remains constant, even though their form and location undergo continual change.
Almost all life on earth is ultimately maintained by transformations of energy from the sun. Plants capture the sun's energy and use it to synthesize complex, energy-rich molecules (chiefly sugars) from molecules of carbon dioxide and water. These synthesized molecules then serve, directly or indirectly, as the source of energy for the plants themselves and ultimately for all animals and decomposer organisms (such as bacteria and fungi). This is the food web: The organisms that consume the plants derive energy and materials from breaking down the plant molecules, use them to synthesize their own structures, and then are themselves consumed by other organisms. At each stage in the food web, some energy is stored in newly synthesized structures and some is dissipated into the environment as heat produced by the energy-releasing chemical processes in cells. A similar energy cycle begins in the oceans with the capture of the sun's energy by tiny, plant-like organisms. Each successive stage in a food web captures only a small fraction of the energy content of organisms it feeds on.
The elements that make up the molecules of living things are continually recycled. Chief among these elements are carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, calcium, sodium, potassium, and iron. These and other elements, mostly occurring in energy-rich molecules, are passed along the food web and eventually are recycled by decomposers back to mineral nutrients usable by plants. Although there often may be local excesses and deficits, the situation over the whole earth is that organisms are dying and decaying at about the same rate as that at which new life is being synthesized. That is, the total living biomass stays roughly constant, there is a cyclic flow of materials from old to new life, and there is an irreversible flow of energy from captured sunlight into dissipated heat.
An important interruption in the usual flow of energy apparently occurred millions of years ago when the growth of land plants and marine organisms exceeded the ability of decomposers to recycle them. The accumulating layers of energy-rich organic material were gradually turned into coal and oil by the pressure of the overlying earth. The energy stored in their molecular structure we can now release by burning, and our modern civilization depends on immense amounts of energy from such fossil fuels recovered from the earth. By burning fossil fuels, we are finally passing most of the stored energy on to the environment as heat. We are also passing back to the atmosphere—in a relatively very short time—large amounts of carbon dioxide that had been removed from it slowly over millions of years.
The amount of life any environment can sustain is limited by its most basic resources: the inflow of energy, minerals, and water. Sustained productivity of an ecosystem requires sufficient energy for new products that are synthesized (such as trees and crops) and also for recycling completely the residue of the old (dead leaves, human sewage, etc.). When human technology intrudes, materials may accumulate as waste that is not recycled. When the inflow of resources is insufficient, there is accelerated soil leaching, desertification, or depletion of mineral reserves.
Force is any influence that causes a free body to undergo a change in speed, a change in direction, or a change in shape. Force can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate, or which can cause a flexible object to deform. A force has both magnitude and direction, making it a vector quantity. Newton's second law, F=ma, can be formulated to state that an object with a constant mass will accelerate in proportion to the net force acting upon and in inverse proportion to its mass, an approximation which breaks down near the speed of light. Newton's original formulation is exact, and does not break down: this version states that the net force acting upon an object is equal to the rate at which its momentum changes.
Related concepts to accelerating forces include thrust, increasing the velocity of the object, drag, decreasing the velocity of any object, and torque, causing changes in rotational speed about an axis. Forces which do not act uniformly on all parts of a body will also cause mechanical stresses,[2] a technical term for influences which cause deformation of matter. While mechanical stress can remain embedded in a solid object, gradually deforming it, mechanical stress in a fluid determines changes in its pressure and volume.
A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
For simplicity sake, all forces (interactions) between objects can be placed into two broad categories:
contact forces, and
forces resulting from action-at-a-distance
Contact forces are those types of forces that result when the two interacting objects are perceived to be physically contacting each other. Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces. These specific forces will be discussed in more detail later in Lesson 2 as well as in other lessons.
Action-at-a-distance forces are those types of forces that result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. Examples of action-at-a-distance forces include gravitational forces. For example, the sun and planets exert a gravitational pull on each other despite their large spatial separation. Even when your feet leave the earth and you are no longer in physical contact with the earth, there is a gravitational pull between you and the Earth. Electric forces are action-at-a-distance forces. For example, the protons in the nucleus of an atom and the electrons outside the nucleus experience an electrical pull towards each other despite their small spatial separation. And magnetic forces are action-at-a-distance forces. For example, two magnets can exert a magnetic pull on each other even when separated by a distance of a few centimeters.
Play is defined as “outside of ordinary life,” not serious,” and “unproductive.” Some authors attribute this work/play distinction to industrialization or to social-class distinctions. What is play’s relationship to “work”? Many scientists think of much of their work as play, often linking the idea of play with high creativity. “Play did not interrupt work,” he says, it just provided another venue for thinking. People often have more brainstorms on the jogging path than at their desks.” “Work and play have always been overlapping categories.” It gives the following outcomes to the human being they are:
• People play at work to seek competence, stimulation, challenge, or reinforcement.
• People who perform very playful tasks enjoy what they are doing. When they judge those activities appropriate, they switch to them readily and try to continue doing them.
• They tend to concentrate more and increase their persistence.
• They become less aware of the passage of time and reluctant to change activities.
• They become so absorbed that they may neglect other things, such as long-term goals, non-playful tasks and social relations.
• Their learning is enhanced because the pleasure and involvement of playful activities induces them to expend time and effort.
• Through different forms of play they can either broaden their behavioral repertoires incrementally, discover or invent radically new behaviors, and polish their existing skills through repetitive practice.
• Playful tasks foster creativity. If the playful tasks are new ones, they will put much effort into learning them and exploring them, usually trying to control their own learning.
There is to a large extent the result of changing technology. Starbuck and Webster attribute much of the erosion of the distinction between play and work to the introduction of PCs into the workplace, since they are “simultaneously fun to use and serious tools.”
Types of forces
A force is any influence that causes a free body to undergo a change in speed, a change in direction, or a change in shape. Force can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate, or which can cause a flexible object to deform. A force has both magnitude and direction, making it a vector quantity. Newton's second law, F=ma, can be formulated to state that an object with a constant mass will accelerate in proportion to the net force acting upon and in inverse proportion to its mass, an approximation which breaks down near the speed of light. Newton's original formulation is exact, and does not break down: this version states that the net force acting upon an object is equal to the rate at which its momentum changesces
] Sir Isaac Newton sought to describe the motion of all objects using the concepts of inertia and force, and in doing so he found that they obey certain conservation laws. In 1687 Newton went on to publish his thesis Philosophiae Naturalis Principia Mathematica.[4][10] In this work Newton set out three laws of motion that to this day are the way forces are described in physics.[10]
[edit]Newton's first law
Main article: Newton's laws of motion#Newton's first law
Newton's first law of motion states that objects continue to move in a state of constant velocity unless acted upon by an external net force or resultant force.[10] This law is an extension of Galileo's insight that constant velocity was associated with a lack of net force (see a more detailed description of this below). Newton proposed that every object with mass has an innate inertia that functions as the fundamental equilibrium "natural state" in place of the Aristotelian idea of the "natural state of rest". That is, the first law contradicts the intuitive Aristotelian belief that a net force is required to keep an object moving with constant velocity. By making rest physically indistinguishable from non-zero constant velocity, Newton's first law directly connects inertia with the concept of relative velocities. Specifically, in systems where objects are moving with different velocities, it is impossible to determine which object is "in motion" and which object is "at rest". In other words, to phrase matters more technically, the laws of physics are the same in every inertial frame of reference, that is, in all frames related by a Galilean transformation.
For example, while traveling in a moving vehicle at a constant velocity, the laws of physics do not change from being at rest. A person can throw a ball straight up in the air and catch it as it falls down without worrying about applying a force in the direction the vehicle is moving. This is true even though another person who is observing the moving vehicle pass by also observes the ball follow a curving parabolic path in the same direction as the motion of the vehicle. It is the inertia of the ball associated with its constant velocity in the direction of the vehicle's motion that ensures the ball continues to move forward even as it is thrown up and falls back down. From the perspective of the person in the car, the vehicle and everything inside of it is at rest: It is the outside world that is moving with a constant speed in the opposite direction. Since there is no experiment that can distinguish whether it is the vehicle that is at rest or the outside world that is at rest, the two situations are considered to be physically indistinguishable. Inertia therefore applies equally well to constant velocity motion as it does to rest.
The concept of inertia can be further generalized to explain the tendency of objects to continue in many different forms of constant motion, even those that are not strictly constant velocity. The rotational inertia of planet Earth is what fixes the constancy of the length of a day and the length of a year. Albert Einstein extended the principle of inertia further when he explained that reference frames subject to constant acceleration, such as those free-falling toward a gravitating object, were physically equivalent to inertial reference frames. This is why, for example, astronauts experience weightlessness when in free-fall orbit around the Earth, and why Newton's Laws of Motion are more easily discernible in such environments. If an astronaut places an object with mass in mid-air next to herself, it will remain stationary with respect to the astronaut due to its inertia. This is the same thing that would occur if the astronaut and the object were in intergalactic space with no net force of gravity acting on their shared reference frame. This principle of equivalence was one of the foundational underpinnings for the development of the general theory of relativity.[11]
Though Sir Isaac Newton's most famous equation is , he actually wrote down a different form for his second law of motion that did not use differential calculus.
[edit]Newton's second law
Main article: Newton's laws of motion#Newton's second law
A modern statement of Newton's second law is a vector differential equation:[12]
where is the momentum of the system, and is the net (vector sum) force. In equilibrium, there is zero net force by definition, but (balanced) forces may be present nevertheless. In contrast, the second law states an unbalanced force acting on an object will result in the object's momentum changing over time.[10]
By the definition of momentum,
where m is the mass and is the velocity.
In a system of constant mass, the use of the constant factor rule in differentiation allows the mass to move outside the derivative operator, and the equation becomes
.
By substituting the definition of acceleration, the algebraic version of Newton's second law is derived:
It is sometimes called the "second most famous formula in physics".[13] Newton never explicitly stated the formula in the reduced form above.
Newton's second law asserts the direct proportionality of acceleration to force and the inverse proportionality of acceleration to mass. Accelerations can be defined through kinematic measurements. However, while kinematics are well-described through reference frame analysis in advanced physics, there are still deep questions that remain as to what is the proper definition of mass. General relativity offers an equivalence between space-time and mass, but lacking a coherent theory of quantum gravity, it is unclear as to how or whether this connection is relevant on microscales. With some justification, Newton's second law can be taken as a quantitative definition of mass by writing the law as an equality; the relative units of force and mass then are fixed.
The use of Newton's second law as a definition of force has been disparaged in some of the more rigorous textbooks,[3][14] because it is essentially a mathematical truism. Notable physicists, philosophers and mathematicians who have sought a more explicit definition of the concept of force include Ernst Mach, Clifford Truesdell and Walter Noll.[15]
Newton's second law can be used to measure the strength of forces. For instance, knowledge of the masses of planets along with the accelerations of their orbits allows scientists to calculate the gravitational forces on planets.
[edit]Newton's third law
Main article: Newton's laws of motion#Newton's third law: law of reciprocal actions
Newton's third law is a result of applying symmetry to situations where forces can be attributed to the presence of different objects. For any two objects (call them 1 and 2), Newton's third law states that any force that is applied to object 1 due to the action of object 2 is automatically accompanied by a force applied to object 2 due to the action of object 1[16]
This law implies that forces always occur in action-and-reaction pairs.[10] If object 1 and object 2 are considered to be in the same system, then the net force on the system due to the interactions between objects 1 and 2 is zero since
This means that in a closed system of particles, there are no internal forces that are unbalanced. That is, action-and-reaction pairs of forces shared between any two objects in a closed system will not cause the center of mass of the system to accelerate. The constituent objects only accelerate with respect to each other, the system itself remains unaccelerated. Alternatively, if an external force acts on the system, then the center of mass will experience an acceleration proportional to the magnitude of the external force divided by the mass of the system.[3]
Combining Newton's second and third laws, it is possible to show that the linear momentum of a system is conserved. Using
and integrating with respect to time, the equation:
is obtained. For a system which includes objects 1 and 2,
which is the conservation of linear momentum.[17] Using the similar arguments, it is possible to generalizing this to a system of an arbitrary number of particles. This shows that exchanging momentum between constituent objects will not affect the net momentum of a system. In general, as long as all forces are due to the interaction of objects with mass, it is possible to define a system such that net momentum is never lost nor gained.
Types of Forces
There are nine types of forces you can apply to simulations, each described in this section. Each force is represented by its own control object, which can be selected, transformed, rotated, and scaled like any other object in the scene. For example, you can animate the rotation of a fan’s control object to create the effect of a classic oscillating fan. Scaling a force’s control object changes its strength (amplitude) accordingly.
Attractor
Drag
Eddy
Toric
Turbulence
Wind
Attractor (Magnet)
The attractor attracts or repels ICE particles, hair, or rigid bodies much like a magnet attracts/repels iron filings, depending on whether you specify a positive or negative value for the Amplitude (strength). Positive values repel objects from the attractor control object while negative values attract them to its center.
Rigid bodies are attracted to the attractor’s center when they’re inside the sphere.
You can set the attractor’s range of influence so that the magnetic field will have an effect only on objects that are within the number of Softimage units that you specify.
You can also set the decay of the attractor to have maximum force at the center and minimum at the edges, or the reverse (with negative values) with minimum force at the center and maximum at the edges.
Drag
The drag force opposes the movement of ICE particles, rigid bodies, and hair as if they were in a medium, such as fluid. This give a more direct level of control when you want to slow down particles or hairs. For example, you could create the effect of hair moving under water using the drag force or create a slow-motion effect of particles as they are being emitted.
In the image below, the particles are slowed down by the drag force, as if they are moving through a thick fluid.
You can control the drag’s amplitude, which is the strength of the force. You can also set the flow type to be either Laminar (a smooth and regular flow) or Turbulent (an irregular, more chaotic flow).
The basic drag force formula uses the cross-sectional area of the simulated object (Assume Size option) as the scaling factor, but you can set the Radius which calculates the drag using an area value in Softimage units that you specify.
Eddy (Vacuum)
An eddy force simulates the effect of a vacuum or local turbulence on ICE particles, rigid bodies, hair, and cloth by creating a vortex force field inside a cylinder. Anything that is inside the cylinder is affected by the force.Rigid bodies are swirled around inside the eddy control object, then are flung out as they leave the control object.
You can control the eddy’s flow velocity, which is the speed of the force. As well, you can use the eddy’s flow viscosity to create a drag effect on the simulated objects.
To control the eddy’s area of influence, you can adjust the size of its radius and length of its cylinder.
The force is defined along the cylinder’s axis and in a radius. For the force going in a radial direction, negative values attract objects toward the cylinder axis, while positive values push objects away from it.
The eddy’s intensity falls off (decays) from the cylinder’s center to its outer edge (radius), and moves from the bottom to the top of the axis. You can adjust the falloff for both the radial and axial decay.
Fan
The fan creates a “local” effect of wind blowing through a cylinder so that everything inside the cylinder is affected. The fan’s wind direction follows the cylinder’s axis.
Rigid bodies that are within the fan control object are pushed away from it.
You can control the fan’s velocity, which is its speed. As well, you can use the fan’s flow viscosity to create a drag effect on the simulated objects.
To control the fan’s area of influence, you can adjust the size of the radius and length of its cylinder.
The fan’s intensity falls off (decays) from the cylinder’s center to its outer edge (radius), and moves from the bottom to the top of the axis (its drop length). You can adjust the intensity’s falloff for both the radial (across its axis) and axial (along its length) decay.
Gravity
Gravity is the most common type of “force” that you will use, for obvious reasons. Gravity is actually an acceleration that is the same for all objects regardless of their mass: every object falls at the same rate (remember Galileo and Newton?). However, everything changes at the moment there is air resistance/friction or when the object collides with another because that’s where its mass, energy, and momentum play a major role.
To have the correct gravitational behavior from the objects, the size of the objects in the scene must be taken into consideration. In Softimage, the default gravity is set to 98.1, which is earth’s gravity if you define 1 Softimage unit as 10 cm. This scale is used because most characters are modeled with a scale of 1 unit equalling 10 cm, and it is also the scale used for the default Softimage rigs and models.
However, if you define 1 Softimage unit as 1 meter, you would need to set the gravity to 9.81. Depending on the scale of objects in your scene, you may need to adjust this value (including a negative value) to get objects falling as they should.
Toric
The toric force is similar to an eddy except that it is in the shape of a torus (also known as a donut, which tastes better). It simulates the effect of a vacuum or local turbulence by creating a vortex force field inside the torus. Anything that is inside the torus is affected by the force.
This force is useful for making billowing effects in smoke simulations or having ICE particles or rigid bodies “sucked” through a tube to follow a path. If you want to do effects such as mushroom clouds or billowing smoke, use a drag force working in conjunction with this one.
You can keep the torus closed (360 degrees) or you can have it open. This can be useful for having particles travel through one or more open-ended toric forces as if they were being piped through a straw.
Rigid bodies get sucked into the torus and swirl along its main circumference. When they go outside of the toric control object, they get flung off into space.
You can control the size of the toric force by setting its main radius (essentially the size of the torus) and the cross-section, which is the thickness of the torus.
You can use the toric force’s flow viscosity to create a drag effect on the simulated objects.
The torus force has three different Flow Velocity components:
• The Around Axis is the strength of the force that pushes the simulated objects (spins them) around the cross-section the torus in a cyclical way.
• The Away From Axis strength attracts objects toward or repels them away from the main axis.
• The Around Torus strength moves objects along the main torus axis through the tube.
As well, you can set the decay (falloff) of the amplitude as objects are farther away from the main axis.
Turbulence
Turbulence creates allover random noise patterns on simulated objects. This could be useful for creating starfields, for example, or foggy or smoky atmospheric effects when used with a sprite shader.
If you’re using ICE particles, you can use the Turbulence node or Turbulize compounds to deform an object by perturbing its points, such as for creating ocean wave-like effects on a grid.
Turbulence generates a random noise among the rigid bodies as the simulation starts. In this case, the turbulence is applied only along the X axis.
You can set the amplitude (strength) of the turbulence using either positive or negative values.
You can choose to use either Perlin or Simplex noise:
• Perlin noise has spatial coherence, meaning that several different points in roughly the same location in space tend to have similar noise added to them. It interpolates between the random values. Perlin noise can help make objects more natural-looking by imitating the controlled random appearance of elements found in nature; that is, there is structure to the noise while still appearing fairly random.
• Simplex noise is similar to Perlin noise, but is less computationally complex. This is because it divides the space into equilateral triangles to interpolate between, which reduces the number of data points. This makes Simplex noise useful for producing noise over large spatial areas.
Simplex noise has a well-defined and continuous gradient everywhere that can be computed fairly quickly, and has no noticeable directional artifacts.
The Frequency parameters determine the number of times the noise pattern is repeated on each axis that you choose. You can also set the noise frequency over time (in frames), letting you speed up or slow down the whole effect.
You can also add a fractal-type of complexity to the noise which increases the level of detail.
Vortex
The vortex simulates a spiralling, swirling movement on ICE particles, rigid bodies, or hair.
Rigid bodies swirl around the axis inside the vortex control object. With Local selected, the rigid bodies are affected only when they’re within the sphere. When they go outside of the control object, they are flung off into space.
You can control the vortex amplitude, which is the strength of the force, including a radial component. You can set the vortex’s range of influence so that the vortex will have an effect only on objects that are within the number of Softimage units that you specify.
You can also set the decay of the vortex to have maximum force at the center and minimum at the edges, or the reverse (with negative values) with minimum force at the center and maximum at the edges.
Wind
The wind force creates the effect of wind blowing on the simulated objects. You can control the wind’s velocity (speed) and its flow viscosity, which creates a drag effect on the simulated objects.
If there are no other forces at work on an ICE particle simulation except wind, particles will eventually reach the speed of the wind’s velocity setting which, in some cases, can actually slow down the particle velocity at emission. This is because particles have an initial velocity of their own when they’re emitted
Forms of Energy
Mechanical energy
Mechanical energy puts something in motion. It moves cars and lifts elevators. A machine uses mechanical energy to do work. The mechanical energy of a system is the sum of its kinetic and potential energy. Levers, which need a fulcrum to operate, are the simplest type of machine. Wheels, pulleys and inclined planes are the basic elements of most machines.
Chemical energy
Chemical energy is the energy stored in molecules and chemical compounds, and is found in food, wood, coal, petroleum and other fuels. When the chemical bonds are broken, either by combustion or other chemical reactions, the stored chemical energy is released in the form of heat or light. For example, muscle cells contain glycogen. When the muscle does work the glycogen is broken down into glucose. When the chemical energy in the glucose is transferred to the muscle fibers some of the energy goes into the surroundings as heat.
Electrical energy
Electrical energy is produced when unbalanced forces between electrons and protons in atoms create moving electrons called electric currents. For example, when we spin a copper wire through the poles of a magnet we induce the motion of electrons in the wire and produce electricity. Electricity can be used to perform work such as lighting a bulb, heating a cooking element on a stove or powering a motor. Note that electricity is a "secondary" source of energy. That means other sources of energy are needed to produce electricity.
Radiant energy
Radiant energy is carried by waves. Changes in the internal energy of particles cause the atoms to emit energy in the form of electromagnetic radiation which includes visible light, ultraviolet (UV) radiation, infrared (IR) radiation, microwaves, radio waves, gamma rays, and X-rays.
Electromagnetic radiation from the sun, particularly light, is of utmost importance in environmental systems because biogeochemical cycles and virtually all other processes on earth are driven by them.
Thermal energy
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
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
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.
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
Examples of the transformation of different energy forms.
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.
Animation: Fuel Cell Vehicle
Energy Units
1 British Thermal Unit = 1055 Joules.
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</dd>
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/second</dd>
Power is sometimes measured in horsepower (hp):
1 horsepower = 746 Watts</dd>
Electrical energy is generally expressed in kilowatt-hours (kWh):
1 kilowatt-hour = 3,600,000 Joules</dd>
It is important to realize that a kilowatt-hour is a unit of energy not power. For example, an iron rated at 2000 Watts would consume 2 x 3.6 106 J of energy in 1 hour.
Heat energy is often measured in calories. One calorie (cal) is defined as the heat required to raise the temperature of 1 gram of water from 14.5 to 15.5 ºC:
1 calorie = 4.189 Joules</dd>
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 to 64ºF
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