{"id":16611,"date":"2018-01-19T16:26:32","date_gmt":"2018-01-19T16:26:32","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=16611"},"modified":"2022-11-08T08:08:11","modified_gmt":"2022-11-08T08:08:11","slug":"what-is-mechanical-energy","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-mechanical-energy\/","title":{"rendered":"What is Mechanical Energy"},"content":{"rendered":"<div   id="8n9s8rpp6h"    class=\"su-quote su-quote-style-default\"><div   id="8n9s8rpp6h"    class=\"su-quote-inner su-u-clearfix su-u-trim\">In physics, <strong>mechanical energy<\/strong> (E<sub>mech<\/sub>) is the energy associated with the <strong>motion<\/strong> and<strong> position<\/strong> of an object, usually in some force field (e.g.,, gravitational field).<\/div><\/div>\n<p><strong>Mechanical energy<\/strong> (and thermal energy) can be separated into two categories, transient and stored. Transient energy is energy in motion, that is, energy being transferred from one place to another. Stored energy is the energy contained within a substance or object. Transient mechanical energy is commonly referred to as <strong>work<\/strong>. Stored mechanical energy exists in one of two forms: <strong>kinetic<\/strong> or <strong>potential<\/strong>:<\/p>\n<ul>\n<li><strong>Potential energy<\/strong>. Potential energy, U, is defined as the energy stored in an object subjected to a conservative force. Common types include the gravitational potential energy of an object that depends on its mass and its distance from the center of mass of another object.<\/li>\n<li><strong>Kinetic energy<\/strong>. The kinetic energy, <em>K<\/em>, is defined as the energy stored in an object because of its motion. It depends on the speed of an object and is the ability of a moving object to do work on other objects when it collides with them.<\/li>\n<\/ul>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum.png\"><img loading=\"lazy\" class=\"size-full wp-image-15713 aligncenter\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum.png\" alt=\"conservartion-of-mechanical-energy-pendulum\" width=\"282\" height=\"214\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum.png 282w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum-180x138.png 180w\" sizes=\"(max-width: 282px) 100vw, 282px\" \/><\/a><\/p>\n<div   id="8n9s8rpp6h"    class=\"collapsible-container\">\n<h2>Conservation of Mechanical Energy<\/h2>\n<p>First, the principle of the <strong>Conservation of Mechanical Energy<\/strong> was stated:<\/p>\n<p style=\"text-align: left;\"><em><span style=\"font-size: 18px;\"><strong>The total mechanical energy<\/strong> (defined as the sum of its potential and kinetic energies) of a particle being acted on by only conservative forces<strong> is constant<\/strong>.<\/span><\/em><\/p>\n<p><strong><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-example.png\"><img loading=\"lazy\" class=\"alignright size-full wp-image-15711\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-example.png\" alt=\"conservartion-of-mechanical-energy-example\" width=\"194\" height=\"172\" \/><\/a><\/strong><\/p>\n<p>See also: <a title=\"Conservation of Mechanical Energy\" href=\"http:\/\/sitepourvtc.com\/laws-of-conservation\/law-of-conservation-of-energy\/conservation-of-mechanical-energy\/\">Conservation of Mechanical Energy<\/a>.<\/p>\n<p><strong>An isolated system<\/strong> is one in which <strong>no external force<\/strong> causes energy changes. If only <strong>conservative forces<\/strong> act on an object and <strong>U<\/strong> is the<strong> potential energy<\/strong> function for the total conservative force, then:<\/p>\n<p style=\"text-align: center;\"><em><span style=\"font-size: 18px;\"><strong>E<\/strong><strong><sub>mech<\/sub><\/strong><strong> = U + K<\/strong><\/span><\/em><\/p>\n<p><strong>The potential energy, <em>U<\/em><\/strong>, depends on the position of an object subjected to a conservative force.<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/potential-energy-equation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-15710\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/potential-energy-equation.png\" alt=\"potential-energy-equation\" width=\"176\" height=\"71\" \/><\/a><\/p>\n<p>It is defined as the object&#8217;s ability to do work and is increased as the object is moved in the opposite direction of the direction of the force.<\/p>\n<p><strong>The potential energy<\/strong> associated with a system consisting of Earth and a nearby particle is\u00a0<strong>gravitational potential energy<\/strong>.<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/gravitational-potential-energy-equation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-15712\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/gravitational-potential-energy-equation.png\" alt=\"gravitational-potential-energy-equation\" width=\"256\" height=\"45\" \/><\/a><\/p>\n<p><strong>The kinetic energy, <em>K<\/em><\/strong>, depends on the speed of an object and is the ability of a moving object to do work on other objects when it collides with them.<\/p>\n<p style=\"text-align: center;\"><em><span style=\"font-size: 18px;\"><strong>\u00a0K = \u00bd mv<sup>2<\/sup><\/strong><\/span><\/em><\/p>\n<p>The definition mentioned above (<strong>E<\/strong><strong><sub>mech<\/sub><\/strong><strong> = U + K<\/strong>) assumes that the system is <strong>free of friction<\/strong> and other <a title=\"Conservative \u2013 Nonconservative Forces\" href=\"http:\/\/sitepourvtc.com\/laws-of-conservation\/law-of-conservation-of-energy\/conservative-nonconservative-forces\/\"><strong>non-conservative forces<\/strong><\/a>. The difference between a conservative and a non-conservative force is that when a conservative force moves an object from one point to another, the work done by the conservative force is independent of the path.<\/p>\n<p>In any real situation, <strong>frictional forces<\/strong> and other non-conservative forces are present. Still, their effects on the system are so small that the principle of <strong>conservation of mechanical energy<\/strong> can be used as a fair approximation in many cases. For example, the frictional force is a non-conservative force because it reduces the mechanical energy in a system.<\/p>\n<p>Note that non-conservative forces do not always reduce mechanical energy. A non-conservative force changes the mechanical energy. Some forces increase the total mechanical energy, like the force provided by a motor or engine, which is also a non-conservative force.<\/p>\n<h2>Example: Block sliding down a frictionless incline slope<\/h2>\n<p>The 1 kg block starts at a height H (let say 1 m) above the ground, with <strong>potential energy<\/strong> <strong>mgH<\/strong> and<strong> kinetic energy<\/strong> equal to 0. It slides to the ground (without friction) and arrives with no potential energy and kinetic energy <strong>K = \u00bd mv<sup>2<\/sup><\/strong>. Calculate the velocity of the block on the ground and its kinetic energy.<br \/>\n<span style=\"font-size: 25px;\"><br \/>\n<strong><em>E<\/em><\/strong><strong><em><sub>mech<\/sub><\/em><\/strong><strong><em> = U + K = const<\/em><\/strong><\/span><\/p>\n<p><strong><em>=&gt; \u00bd mv<\/em><\/strong><strong><em><sup>2<\/sup><\/em><\/strong><strong><em> = mgH<\/em><\/strong><\/p>\n<p><strong><em>=&gt; v = \u221a2gH = 4.43 m\/s<\/em><\/strong><\/p>\n<p><strong><em>=&gt; K<\/em><\/strong><strong><em><sub>2<\/sub><\/em><\/strong><strong><em> = \u00bd x 1 kg x (4.43 m\/s)<\/em><\/strong><strong><em><sup>2<\/sup><\/em><\/strong><strong><em> = 19.62 kg.m<\/em><\/strong><strong><em><sup>2<\/sup><\/em><\/strong><strong><em>.s<\/em><\/strong><strong><em><sup>-2<\/sup><\/em><\/strong><strong><em> = 19.62 J<\/em><\/strong><\/p>\n<h2>Example: Pendulum<\/h2>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum.png\"><img loading=\"lazy\" class=\"alignright size-full wp-image-15713\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum.png\" alt=\"conservartion-of-mechanical-energy-pendulum\" width=\"282\" height=\"214\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum.png 282w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum-180x138.png 180w\" sizes=\"(max-width: 282px) 100vw, 282px\" \/><\/a>Assume a <strong>pendulum<\/strong> (ball of mass m suspended on a string of length <strong>L<\/strong> that we have pulled up so that the ball is a height <strong>H &lt; L<\/strong> above its lowest point on the arc of its stretched string motion. The pendulum is subjected to the <strong>conservative gravitational force<\/strong> where frictional forces like air drag and friction at the pivot are negligible.<\/p>\n<p>We release it from rest. <strong>How fast is it going at the bottom?<\/strong><\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum2.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-15714\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum2.png\" alt=\"conservartion-of-mechanical-energy-pendulum2\" width=\"322\" height=\"115\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum2.png 322w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum2-300x107.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/conservartion-of-mechanical-energy-pendulum2-320x115.png 320w\" sizes=\"(max-width: 322px) 100vw, 322px\" \/><\/a><\/p>\n<p>The pendulum reaches the <strong>greatest kinetic energy<\/strong> and <strong>least potential energy<\/strong> when in the <strong>vertical position<\/strong>\u00a0because it will have the greatest speed and be nearest the Earth at this point. On the other hand, it will have its <strong>least kinetic energy<\/strong> and <strong>greatest potential energy<\/strong> at the <strong>extreme positions<\/strong> of its swing because it has zero speed and is farthest from Earth at these points.<\/p>\n<p>If the amplitude is limited to small swings, the period <em>T<\/em> of a simple pendulum, the time is taken for a complete cycle, is:<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/period-of-pendulum-conservation-of-energy.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-15715\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/10\/period-of-pendulum-conservation-of-energy.png\" alt=\"period-of-pendulum-conservation-of-energy\" width=\"252\" height=\"77\" \/><\/a><\/p>\n<p>where <strong><em>L<\/em><\/strong> is the length of the pendulum and <strong><em>g<\/em><\/strong> is the local acceleration of gravity. For small swings, the period of swing is approximately the same for different size swings. That is, <strong>the period is independent of amplitude<\/strong>.<\/p>\n<\/div>\n<div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:20px 0;border-width:2px;border-color:#999999\"><\/div>\n<div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\u00a0 <div   id="8n9s8rpp6h"    class=\"su-accordion su-u-trim\"><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>References:<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\"><strong>Reactor Physics and Thermal Hydraulics:<\/strong>\n<ol>\n<li>J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading,\u00a0MA (1983).<\/li>\n<li>J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.<\/li>\n<li>W. M. Stacey, Nuclear Reactor Physics, John Wiley &amp; Sons, 2001, ISBN: 0- 471-39127-1.<\/li>\n<li>Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering,\u00a0Springer; 4th edition, 1994, ISBN:\u00a0978-0412985317<\/li>\n<li>Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC\u00a0Press; 2\u00a0edition, 2012, ISBN:\u00a0978-0415802871<\/li>\n<li>Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN:\u00a0978-3-319-13419-2<\/li>\n<li>Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition,\u00a0John Wiley &amp; Sons, 2006, ISBN:\u00a0978-0-470-03037-0<\/li>\n<li>Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010,\u00a0ISBN 978-1-4020-8670-0.<\/li>\n<li>U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2, and 3. June 1992.<\/li>\n<\/ol>\n<\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-default\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See above:<\/h2>\n<p>Energy<a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/p><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Mechanical energy (and thermal energy) can be separated into two categories, transient and stored. Transient energy is energy in motion, that is, energy being transferred from one place to another. Stored energy is the energy contained within a substance or object. Transient mechanical energy is commonly referred to as work. Stored mechanical energy exists in &#8230; <a title=\"What is Mechanical Energy\" class=\"read-more\" href=\"https:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-mechanical-energy\/\" aria-label=\"More on What is Mechanical Energy\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":16542,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"generate_page_header":""},"_links":{"self":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/16611"}],"collection":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/comments?post=16611"}],"version-history":[{"count":3,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/16611\/revisions"}],"predecessor-version":[{"id":34786,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/16611\/revisions\/34786"}],"up":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/16542"}],"wp:attachment":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/media?parent=16611"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}