Work vs Heat
Work and heat are the two most important concepts of thermodynamics. Work and heat are highly interrelated, but they are not quite the same. The quest to understand work and heat goes way back. With these two concepts cleared, classical thermodynamics became one of the “completed” fields in physics. Both heat and work are concepts of energy. Theories of heat and work have a huge significance in thermodynamics, motor mechanics and machinery. In this article, we are going to discuss the definition, similarities, and differences between heat and work.
In physics work is defined as the amount of energy transferred by a force acting through a distance. Work is a scalar quantity, which means there is only a magnitude to work, a direction is not present. Consider an object being dragged on a rough surface. There is friction acting on the object. For given points A and B, infinite number of paths exist between them, therefore, there are infinitely many routes to take the box from A to B. If the distance the box travels when it is taken on a certain path is x, the work done by friction on the box is F.x, considering only the scalar values. Different paths have different x values. Therefore, work done is different. It can be proved that the work is dependent on the path taken, which means work is a function of path. For a conservative force field, the work done can be taken as a function of the state. The SI unit of work is Joule, named in honor of the English physicist James Joule. The CGS unit of work is erg. Other units are foot-pound, foot-poundal and liter-atmosphere. In thermodynamics, work is usually referred to as the pressure work, because the internal or external pressure is the force generator that does the work. In a constant pressure situation, the work done can be taken as P.ΔV, where p is the pressure and ΔV is the change in volume.
Heat is a form of energy. Heat is also measured in Joule. The first law of thermodynamics is about the conservation of energy. It states that the heat supplied to a system is equal to the internal energy increment of that system plus the work done by the system on the surrounding. This shows that heat can be converted into work, and work can be converted into heat. Heat is defined as the energy stored as random motion of molecules or atoms. The amount of heat in a system, only depends on the state the system is in; therefore, heat is a function of the state.
What is the difference between Heat and Work?
– Heat is the random motion of molecules, while work is the ordered motion in one direction.
– It can be proven that work can be totally converted to heat, but heat cannot be 100% converted to work.
– In such a heat to work conversion, the randomness of the universe decreases. This is forbidden by the second law of thermodynamics.
– Heat is a function of state, while work is a function of path.
– Heat is a form of energy, while work is a method of transferring energy.