Come to think of it, the work done on a body is converted into some form of energy.But why is it that it ultimately tends to produce heat? In physics we all talk about energy dissipation in the form of heat,but why not electricity, or even light(somehow or the other it tends to form heat,exceptions barred).Why is thermal death,so prevalent a term for non usable energy, and not, say 'electrical death'?What specific mechanism, if any, exists to see to it that all energy is wasted as heat,and not as some other non usable form ?
[Physics] Why does work done ultimately culminate as wasted heat
dissipationenergyenergy-conservationthermodynamics
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What you say is correct in principle, but ignores the important fact that practical car engines are horribly inefficient, and their effeciency changes quite a bit over the range of speed and power required to move the car. Note that this is the point of transmissions. At best they don't loose any power, but they make the overall process more efficient by allowing the gasoline engine to operate at a more efficient point.
In one way, you can look at a hybrid as having a wide-ranging finely adjustable transmission, but there's more to it than that. The efficiency of a gasoline engine is in part related to what fraction of peak power it must put out. If the gas engine is the only mechanical output in the car, then it must be sized to supply peak power. However, most of the time much less than peak power is needed, so the engine often runs at a inefficient point.
With a electric motor available to fill in the when peak power is demanded, the gas engine can be sized smaller and it is easier to make it more efficient over most of the normal operating range. It also allows for the option of not using the gas engine at all at very low power levels where it would be very inefficient. Instead it can effectively be run in bursts of more efficient operation. For example, if the gas engine is 3% efficient at 500 W, but 6% efficient at 1 kW, then you're better off running it at 1 kW half the time instead of at 500 W all the time. With a hybrid, you have this option. With just a gas engine, it's stuck having to produce whatever power is demanded at the moment, regardless of how efficient that is.
I have a Honda Civic hybrid, and I can tell you this stuff really works. I routinely get 50 miles/gallon minimum on the highway, often substantially more. The engine is physically small for the size car, and it has been specially designed to be easily shut down and restarted. Going down a hill, even at highway speeds, the engine often turns off. If the hill is steep enough, the motor is run as a generator and charges the battery. When I get to the bottom of the hill, I can see that for a little while the control system uses the electric motor to keep the car going at the set speed (this is all with cruise control engaged), then eventually gives up and switches on the gas engine. I can feel a slight klunk when that happens, and the charge indicator goes abruptly from discharge to charge.
To turn thermal energy into useful work completely one would need a thermal bath at the temperature of absolute zero. This is explicitly forbidden by the third law of thermodynamics. The best one can do is given by the efficiency of the (theoretical) Carnot cycle: http://en.wikipedia.org/wiki/Carnot_cycle. Th efficiency of the Carnot cycle only depends on the ratio of the temperatures of the cold and the hot thermal baths that a cyclical thermodynamic machine has access to:
$\eta= 1 - T_{cold}/T_{hot}$.
As you can see from the formula, if $T_{cold}=0$, then the efficiency would be equal to one, i.e. all thermal energy would be converted. That, as we said, is forbidden, because of $T_{cold}>0$. On the other hand, if $T_{cold} =T_{hot}$, then the efficiency of any thermal machine is zero, i.e. one can't extract any useful energy from just one temperature bath.
Practical efficiencies that can be reached with real thermal machines range up to 60% (in combined cycle natural gas plants, I believe), but it becomes increasingly more expensive to improve efficiencies, so at some point the cost of the improvement is higher than the cost of the lost energy, at which point economics sets a limit to energy efficiency. A better way to use the lost heat is for heating purposes. Combining a small power plant with the heating systems of buildings makes almost 100% use of the energy in the fuels that are being burned in the power plant. These cogeneration facilities (named so because they produce electricity and useful heat) are playing an increasingly larger role in energy efficiency improvements.
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Heat means collisions.
Energy can be dissipated by radiation (light or photons). The coined term is "radiative losses". It is a very important source of losses for circular beam accelerators (or any sort of device accelerating charged particles, say an antenna) and for spacecraft re-entering the atmosphere before crashing/landing on Earth. A very import notion regarding radiatives losses it that of black bodies. A human body dissipates more energy through radiation as a black body (to keep its temperature at 37°C) than by doing work (moving, talking, thinking, etc.).
A key notion for your further reading: entropy.
Entropy is studied through statistical physics (from which can be derived thermodynamics as a limit case).
Transfer of momentum from particles can be considered as a random process with an uncertainty about how much momentum is transferred from one particle to another.
The transfer of momentum depends on the angle of collision, the momentum of particles colliding and the cross section of the collision. The cross section contains information about the physical interaction (hard spheres, coulomb force, etc.) that we call a collision.
Also the collisions between particles happens at such a small scale that quantum mechanical Heisenberg uncertainty theorem must be taken into account, meaning that we can't be sure how two particles will exactly exchange momentum.
All of this results in a spreading of the input energy given to a physical system among its many many components (1 mole = $10^{23}$ particles). That's what we call energy dissipation. To describe the state of a system we then use distributions of momentum, speed and energy (see Maxwell-Boltzmann distribution).
Entropy is the quantity that monitors the behavior of those distributions. Heat then describe a transformation of the distribution (displacement of the distribution mean, flattening of the distribution) that is allowed by how the entropy should evolve (2nd principle of Thermodynamics).
To sum up:
Heat <=> collision <=> random momentum transfer process + uncertainty about quantity of momentum exchanged => change in entropy + modification of the energy distribution <=> dissipation (or waste) of energy