<p>Hi, I am very new to this subject... <br />so... i know that perpetual motion

Question

<p>Hi, I am very new to this subject... <br />so... i know that perpetual motion cant not exist because it breaks the first 2 laws of thermodynamics. (I was supposed to learn this and make a 20min presentation to the class)<br />Just saying perpetual motion cant exist because of the first 2 laws can't be it. I have to explain what the 2 laws are and how they make perpetual motion not possible. The first law is fairly easy to grasp: you cant get something from nothing.<br />But the second law giving me a really hard time to grasp: energy conversion cant be 100% efficient... then it goes on and talks about entropy and the carnot cycle. <br />what is carnot cycle and what is entropy???<br /><br />and the formulas from wiki goes like<br />W = Q1 (1- T2/T1)<br />what does that all mean???<br />then it suggests some thing like<br />W &lt; Q1 ( 1-T2/T1)<br /> how do i calculate the force (heat) wasted during energy conversion???<br />(never learned about this in class so i need help :)</p>

Explanation / Answer

The Carnot cycle is a theoretical thermodynamic cycle.It can be shown that it is the most efficient cycle for converting a given amount of thermal energy into work, or conversely, creating a temperature difference (e.g. refrigeration) by doing a given amount of work. Every thermodynamic system exists in a particular thermodynamic state. When a system is taken through a series of different states and finally returned to its initial state, a thermodynamic cycle is said to have occurred. In the process of going through this cycle, the system may perform work on its surroundings, thereby acting as a heat engine. A system undergoing a Carnot cycle is called a Carnot heat engine, although such a 'perfect' engine is only a theoretical limit and cannot be built in practice. Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when converting energy to work. During this work, entropy accumulates in the system, which then dissipates in the form of waste heat.

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