Work vs Energy: Is the work the same as the energy? Which comes first, energy or work?
The SI unit for both work and energy is Joule
Definition of work
In thermodynamics, work performed by a system is energy transferred by the system to its surroundings, by a mechanism through which the system can spontaneously exert forces on its surroundings. Energy can also transfer from the surroundings to the system; in a sign convention used in physics, such work has a negative magnitude.
Definition of energy
Energy is the ability to bring about change or to do work.
Work and energy both are associated with PV [ pressure x volume]
Work is PV. Energy is how PV generates.
The common unit is the liter- atmosphere. 1 Joule = 0.0098692 liter-atmosphere,
Now, the next part. Work and energy are two completely different concepts.
When we say energy, energy has two parts one is internal energy[ IE]?U stored energy and the second is work energy [PdV].
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dH =?dU + PdV ( 1st law)
IE is a point function/ state variable/ stored energy. Work is path function/ always in transit. Energy is conserved. Work is always moving back and forth a system to surrounding and like a courier ensuring that energy stock does not deplete. Energy is an exact differential. Work is inexact differential.
Energy relates to state quantities that describe equilibrium (e.g., gas, liquid, solid, etc), not the path which the system has taken to reach its present state.
Work is a path function irrespective of the initial and final states of the process.
Question: Which comes first energy or work?
The obvious question is which comes first, energy or work? Obviously, energy comes first. A system can't do work without energy.
Now your points. Mechanical energy is simply kinetic energy and kinetic energy depends only on temperature. Therefore to generate mechanical energy we need two points in a system with different temperatures. We call these points hot and cold reservoirs of thermal energy.
Let us take case of the turbine in a power plant, there are two temperature points, one is the superheated steam temperature and the other is the condenser temperature. Temperature is an intensive property and it is a state function. A fixed quantity of mechanical energy, therefore, generates depending on the state of the system between these two points which makes the turbine spin and do mechanical work.
The total work done to rotate a rigid body through an angle θ about a fixed axis is the sum of the torques integrated over the angular displacement. If the torque is a constant as a function of θ, then?WAB=τ(θB?θA) W A B = τ ( θ B ? θ A ). This is the mechanical work. It depends on the angle of rotation of the turbine. That is how much energy it can convert into rotation. Work is not a fixed quantity. While the energy is.
Internal energy is like a fixed deposit and work energy is your savings account that meets routine expenses. You do not touch fixed deposits as long as there is money in the savings account.
Passionate about metallurgical calculations
2 年Thank you for posting, Nikhilesh Mukherjee . I once thought of an example to put the difference in plain words. In the end, energy transfer (aka heat) os no other that the result of microscopic mechanical interaction between energized particles with say the walls of a heat exchanger. Interactions result into elastic collisions that transfer energy from the higher kinetically energized particles to the lower ones. This explains: Heat cannot occur when there is a difference in the temperature, aka kinetic energy level. Only here, energy is transferrable When it comes to work, I think of a turbine impeller. There, collisions need to provoke rotation of the blades, thus motion of the rotor through the magnetic field. Electrical energy is withdrawn at the other end. Coming back to the inlet fluid, energy can be harnessed if molecules are able to run against the ultimate electricity withdrawal. This is why there is not all energy of the working fluid can be turned into work, thus yielding to an energy utilization rate (work). The highest conversion rates take place at pure electrical machines, where electrons are able to beat any obstacle in the circuit they are flowing through.
junior engineer (production) at grasim industries limited (chemical division)
2 年Thanks
Naval Architecture Course Director @ Lloyd's Training Academy Informa KNECT 365
2 年Nikhilesh Mukherjee, I am afraid that I can't agree. The mechanical work is a form of energy. It depicts how the mechanism allowing increase of kinetic energy. It occurs to me that you think to much in terms of definitions found in thermodynamics. Everything refers to movement of particles even in thermodynamics, Within thermodynamics is difficult to address individual molecule/atom therefore a statistical approach have been introduced. As result large number of particles behaviour are treated modelled like a single one. Of course PV means energy but when is associated with volume variation i.e movement of entire "particle" than it is mechanical work. When is a constant volume i.e. the " particle" doesn't move as whole it is potential energy. Therefore we should not forget the roots and for sure we don't need to move away fro them