{"id":11287,"date":"2026-07-09T14:28:03","date_gmt":"2026-07-09T14:28:03","guid":{"rendered":"https:\/\/www.myengineeringbuddy.com\/blog\/work-done-in-physics\/"},"modified":"2026-07-09T14:28:03","modified_gmt":"2026-07-09T14:28:03","slug":"work-done-in-physics","status":"publish","type":"post","link":"https:\/\/www.myengineeringbuddy.com\/blog\/work-done-in-physics\/","title":{"rendered":"Work Done in Physics"},"content":{"rendered":"\n<h2>What is Work Done in Physics?<\/h2>\n<p>Work done in Physics is entirely different from our usual understanding of day-to-day work like working in an office, doing workouts, etc.<\/p>\n<p>Work done in physics should be taken more as a scientific\/physical definition rather than correlating it with real life. Although many similarities exist, strictly speaking, these are different.<\/p>\n<p>Continue reading further or contact us on WhatsApp to get an <a href=\"https:\/\/www.myengineeringbuddy.com\/online-tutoring\/online-physics-tutor\/\">Online Physics Tutor<\/a> who can explain to you the relevant concepts better.<\/p>\n<p>To better understand work done in Physics, let us see its formula.<\/p>\n\n<h3>Work Done Equation<\/h3>\n<p>The work done by a constant force F when its point of application undergoes a displacement S is defined to be<\/p>\n<p><strong>$W = FScos theta $<\/strong><\/p>\n<p>Here, $theta $ is the angle between <strong>F<\/strong> and <strong>S<\/strong>.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/1-removebg-preview-1-300x110.png\" alt=\"Diagram showing force F and displacement S with angle theta between them\">\n<p>Only the component of <strong>F<\/strong> along <strong>S<\/strong>, that is $Fcos theta$, contributes to the work done. Strictly speaking, the work is done by the source or agent that applies the force.<\/p>\n<p>To understand it better, let us calculate the work done in the below examples.<\/p>\n\n<h3>Example 1<\/h3>\n<p>If we lift a body from rest to a height h, then work done by lifting force F:<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/2-removebg-preview-1-182x300.png\" alt=\"Diagram of a body being lifted to height h by force F\">\n<p>${W_1} = Fhcos 0 = Fh$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/3-removebg-preview-1.png\" alt=\"Equation for work done by lifting force\">\n<p>Again, work done by the force of gravity mg:<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/4-removebg-preview-1.png\" alt=\"Equation for work done by gravity\">\n<p>${W_2} = (mg),(h),cos {180^o}$<\/p>\n<p>${W_2} = &#8211; mgh$<\/p>\n\n<h3>Example 2<\/h3>\n<p>If a body is pulled on a rough horizontal surface through a displacement S:<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/5-removebg-preview-1-300x203.png\" alt=\"Diagram of a body being pulled on a rough horizontal surface\">\n<p>Work done by normal reaction and gravity:<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/6-removebg-preview-2.png\" alt=\"Equation for work done by normal reaction and gravity\">\n<p>${W_N} = NScos {90^o} = 0$<\/p>\n<p>Work done by pulling force F:<\/p>\n<p>${W_F} = FScos {0^o} = FS$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/7-removebg-preview-1-300x18.png\" alt=\"Equation for work done by pulling force F\">\n<p>Work done by frictional force:<\/p>\n<p>${W_f} = f,scos {180^o} = &#8211; f,s$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/8-removebg-preview-300x19.png\" alt=\"Equation for work done by frictional force\">\n\n<h3>How is the Physics Definition of Work Done Different from What People Usually Think?<\/h3>\n<p>Suppose a person is holding a box of mass m on his head for some time (say for two hours). Here, forces acting on the box are (i) mg force along the vertically downward direction and (ii) normal reaction force exerted by his head along the vertically upward direction.<\/p>\n<p>But the displacement of the points of application of forces is zero. So, according to the definition of work done in physics, work done by forces equals zero. One can say that the person holding a box on his head is doing work in daily life.<\/p>\n\n<h2>Calculation of Work Done<\/h2>\n<p>There are three approaches to calculating work done.<\/p>\n<ul>\n<li>Algebraic approach<\/li>\n<li>Graphical approach<\/li>\n<li>Calculus approach<\/li>\n<\/ul>\n<p>The algebraic approach has limited use, whereas the calculus approach is applicable in every situation. The main advantage of the algebraic approach is that one need not know any calculus to find work done.<\/p>\n\n<h3>The Algebraic Approach of Work Done<\/h3>\n<p>When a constant force <strong>F<\/strong> acts on a particle, and the particle moves through a displacement <strong>S<\/strong>, then the force is said to do work W on the particle: $W = {bf{F}} cdot {bf{S}}$<\/p>\n<p>The scalar product of <strong>F<\/strong> and <strong>S<\/strong> can be evaluated as $W = {bf{F}} cdot {bf{S}} = FScos theta $<\/p>\n<p>Here, F is the magnitude of force F, S is the magnitude of displacement <strong>S<\/strong>, and $theta $ is the smaller angle between <strong>F<\/strong> &amp; <strong>S<\/strong>.<\/p>\n<p>$W = FScos theta = F(Scos theta )$<\/p>\n<p>= magnitude of force \u00d7 component of displacement along the direction of the force.<\/p>\n<p>Or, $W = (Fcos theta ) cdot S$<\/p>\n<p>= component of the force in the direction of displacement \u00d7 magnitude of displacement<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/9-removebg-preview-300x117.png\" alt=\"Diagram illustrating force components and displacement for work done calculation\">\n\n<p><strong>Example 1<\/strong><\/p>\n<p>A body of mass m is sliding down on a smooth inclined plane of inclination $theta $. If L is the length of the inclined plane, then work done by the gravitational force is<\/p>\n<p>${W_{gravity}} = FS = (mgsin theta ),L$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/11-removebg-preview-300x103.png\" alt=\"Diagram of a body sliding down a smooth inclined plane\">\n<p>Here $mgsin theta $ is the component of the force of gravity along with displacement L.<\/p>\n\n<p><strong>Example 2<\/strong><\/p>\n<p>Work done in pulling the bob of mass m of a simple pendulum of length L through an angle $theta $ to the vertical using horizontal external force F.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/12-removebg-preview-300x236.png\" alt=\"Diagram of a simple pendulum bob pulled by horizontal external force\">\n<p>Work done by the gravitational force:<\/p>\n<p>${W_{gravity}} = mghcos {180^o}$<\/p>\n<p>$ = &#8211; mgL(1 &#8211; cos theta )$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/13-removebg-preview-300x147.png\" alt=\"Geometric diagram showing height h in pendulum displacement\">\n<p>$cos theta = frac{{L &#8211; h}}{L} = 1 &#8211; frac{h}{L}$<\/p>\n<p>$frac{h}{L} = 1 &#8211; cos theta $<\/p>\n<p>$h = L(1 &#8211; cos theta )$<\/p>\n<p>$sin theta = frac{{AC}}{L}$<\/p>\n<p>$AC = Lsin theta $<\/p>\n<p>Work done by the horizontal external force:<\/p>\n<p>${W_F} = F(AC) = F cdot Lsin theta $<\/p>\n<p>Similarly, work done by tension developed in the string equals zero.<\/p>\n<p>$W = {bf{T}} cdot {bf{S}} = TScos {90^o} = 0$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/14-removebg-preview.png\" alt=\"Diagram showing tension direction perpendicular to displacement in pendulum\">\n\n<h3>Graphical Representation of Work Done<\/h3>\n<p>The area enclosed by the F-S curve and displacement axis gives the amount of work done by the force.<\/p>\n<p><strong>Work = FS = Area (ABCO)<\/strong><\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/15-removebg-preview-300x268.png\" alt=\"F-S graph showing area ABCO representing work done by constant force\">\n<p><strong>Work done by a variable force<\/strong><\/p>\n<p>For small displacement (dx), the work done will be the area of the strip of width dx.<\/p>\n<p>dA = F(x) (dx) = dW<\/p>\n<p>$W = int {dW} = int_{,{x_i}}^{,{x_f}} {F(x)} ,dx$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/16-removebg-preview-300x211.png\" alt=\"F-x graph showing strip of width dx for variable force work calculation\">\n<p>If the area enclosed is above the x-axis, work done is +ve, and if the area enclosed is below the x-axis, work done is \u2013ve.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/17-removebg-preview-300x146.png\" alt=\"F-x graph showing positive and negative work done areas relative to x-axis\">\n\n<h3>Work Done by the Spring Force Graphically (Without Calculus)<\/h3>\n<p>If x is the displacement of the free end of the spring from its equilibrium position, then the spring force can be written as ${F_{spring}} = &#8211; kx$<\/p>\n<p>Here k is the spring constant.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/18-removebg-preview-253x300.png\" alt=\"Diagram of a spring showing displacement x from equilibrium position\">\n<p>The negative sign signifies that the force always opposes the expansion (x &gt; 0) and compression (x &lt; 0) of the spring. In other words, the force tends to restore the system to its equilibrium position.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/19-removebg-preview-300x244.png\" alt=\"Graph of spring force vs displacement showing linear relationship\">\n<p>So, the area enclosed under ${F_{sp}}$ vs x curve and displacement axis:<\/p>\n<p>Area = Area of trapezium $ = frac{1}{2}(k{x_f} + k{x_i}) times ({x_f} &#8211; {x_i})$<\/p>\n<p>Here, $(k{x_f} + k{x_i})$ represents sum of parallel sides and $({x_f} &#8211; {x_i})$ represents separation between parallel sides.<\/p>\n<p>$Area = frac{k}{2}({x_f} + {x_i})({x_f} &#8211; {x_i}) = frac{k}{2}(x_f^2 &#8211; x_i^2)$<\/p>\n<p>But area enclosed below the x-axis is said to be negative.<\/p>\n<p>Work done by the spring $ = &#8211; frac{k}{2}(x_f^2 &#8211; x_i^2)$<\/p>\n\n<h3>Calculus Approach of Work Done<\/h3>\n<p>When the magnitude and direction of a force vary in three dimensions, it can be expressed as a function of the position vector <strong>F<\/strong>(r) or in terms of coordinates <strong>F<\/strong>(x, y, z). The work done by such a force in an infinitesimal displacement dS is<\/p>\n<p>$dW = {bf{F}} cdot {bf{dS}}$<\/p>\n<p>${(W)_{1 to 2}} = int_{,1}^{,2} {{bf{F}} cdot {bf{dS}}} $<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/10-removebg-preview-300x238.png\" alt=\"Diagram showing a curved path from point 1 to point 2 for calculus approach to work done\">\n<p>In terms of rectangular components:<\/p>\n<p>${bf{F}} = {F_x}hat i + {F_y}hat j + {F_z}hat k$ and ${bf{dS}} = ({d_x})hat i + ({d_y})hat j + ({d_z})hat k$<\/p>\n<p>Therefore,<\/p>\n<p>${W_{1 to 2}} = int_{,1}^{,2} {left( {{F_x}hat i + {F_y}hat j + {F_z}hat k} right) cdot left( {{d_x}hat i + {d_y}hat j + {d_z}hat k} right)} $<\/p>\n<p>${W_{1 to 2}} = int_{,{x_1}}^{,{x_2}} {{F_x},dx} + int_{,{y_1}}^{,{y_2}} {{F_y},dy} + int_{,{z_1}}^{,{z_2}} {{F_z},dz} $<\/p>\n\n<h3>Example<\/h3>\n<p>A force ${bf{F}} = (2xhat i + 2hat j + 3{z^2}hat k),N$ is acting on a particle. Find the work done by the force in displacing the body from (1, 2, 3)m to (3, 6, 1)m.<\/p>\n<p><strong>Ans.<\/strong> Work done by force <strong>F<\/strong> can be written in the form:<\/p>\n<p>$W = int_{,{x_i}}^{,{x_f}} {{F_x},dx} + int_{,{y_i}}^{,{y_f}} {{F_y},dy} + int_{,{z_i}}^{,{z_f}} {{F_z},dz} $<\/p>\n<p>$ = int_{,1}^{,3} {2x,(dx)} + int_{,2}^{,6} {2,(dy)} + int_{,3}^{,1} {3{z^2},(dz)} $<\/p>\n<p>$ = 2left[ {frac{{{x^2}}}{2}} right]_1^3 + 2left[ y right]_2^6 + 3left[ {frac{{{x^3}}}{3}} right]_3^1$<\/p>\n<p>= \u2013 10 J<\/p>\n<p>Here (1, 2, 3)m is the initial position co-ordinate of the particle, and (3, 6, 1)m is the final position co-ordinates of the particle.<\/p>\n\n<h3>Work Done by the Spring Force (With Calculus)<\/h3>\n<p>Work done by the spring force for a displacement from ${x_i}$ to ${x_f}$ is given by<\/p>\n<p>${W_{sp}} = int_{,{x_i}}^{,{x_f}} {{F_{sp}}(dx)} = int {( &#8211; kx)(dx)} = &#8211; frac{k}{2}[{x^2}]_{x_i}^{{x_f}}$<\/p>\n<p>${W_{sp}} = &#8211; frac{k}{2}(x_f^2 &#8211; x_i^2)$<\/p>\n\n<h2>Some More Work Done Examples in Physics<\/h2>\n\n<h3>Work Done by Friction<\/h3>\n<p><strong>Ex.:<\/strong> A block of mass m = 250 gram slides down an inclined plane of inclination 37<sup>o<\/sup> with a uniform speed. Find the work done by the friction as the block slides through 1.0 m.<\/p>\n<p><strong>Sol.:<\/strong> In our question, the body is sliding down with uniform speed. Therefore, the net force acting on the block along the incline will be zero.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/20-removebg-preview-300x200.png\" alt=\"Diagram of a block sliding down an inclined plane at 37 degrees\">\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/21-removebg-preview-300x74.png\" alt=\"Free body diagram showing forces on block on inclined plane\">\n<p>Since, ${a_x} = 0,;,sum {{F_x}} = 0,;,{f_k} = mgsin theta $<\/p>\n<p>Now, work done by the friction force: $W = {{bf{f}}_{bf{k}}} cdot {bf{S}} = {f_k}Scos {180^o} = &#8211; {f_k}S$<\/p>\n<p>${W_{{rm{frictional force}}}} = &#8211; mgsin theta cdot S$<\/p>\n<p>$ = &#8211; left( {frac{1}{4}kg} right)(10,m{rm{\/}}{s^2}) times (sin {37^o}) times (1,m) = &#8211; 1.5,Joule$<\/p>\n\n<h3>Work Done by Gravity (Horizontal Surface)<\/h3>\n<p><strong>Ex.:<\/strong> A boy weighing 200 N is to skid through 20 m on a straight road slowly. Find work done by gravity.<\/p>\n<p><strong>Sol.:<\/strong> Here angle between the force of gravity and displacement is $frac{pi }{2}$; therefore, work is done by the gravity.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/22-removebg-preview-300x135.png\" alt=\"Diagram of a boy skidding on a horizontal road showing gravity perpendicular to displacement\">\n<p>${W_{gravity}} = m{bf{g}} cdot {bf{S}} = (mg)(S)cos {90^o} = 0$<\/p>\n<p>Hence, work done by gravity in this situation will be zero.<\/p>\n\n<h3>Work Done by Gravity on an Inclined Plane<\/h3>\n<p><strong>Example:<\/strong> Suppose a weight 5N is moved up a frictionless inclined plane from R to Q. What is work done by the gravity in Joule.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/23-removebg-preview-300x162.png\" alt=\"Diagram of a frictionless inclined plane with weight moved from R to Q\">\n<p><strong>Solution:<\/strong> In the given figure, angle made by m<strong>g<\/strong> and <strong>S<\/strong> is $(cos {90^o} + theta )$.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/24-removebg-preview-300x152.png\" alt=\"Vector diagram showing angle between gravity and displacement on inclined plane\">\n<p>Therefore, work done by the gravity,<\/p>\n<p>$W = mgscos ({90^o} + theta )$<\/p>\n<p>$ = (5N),(5m),( &#8211; sin theta )$<\/p>\n<p>$ = (5N),(m),left( { &#8211; frac{3}{{}}} right) = &#8211; 15,J$<\/p>\n\n<h3>Work Done in a Circular Motion<\/h3>\n<p>In the given figure, a simple pendulum of length l is hanging, one end is kept fixed, and mass m is attached at the lower end. Mass m is projected with some speed ${v_l}$ so that it describes a complete circle. Find work done by gravity as bob of mass m crosses through the highest point of its trajectory.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/26-removebg-preview-300x300.png\" alt=\"Diagram of a simple pendulum completing a full circular path\">\n<p><strong>Ans.:<\/strong> Work done by gravity is<\/p>\n<p>${W_g} = m{bf{g}} cdot {bf{S}} = mgscos {180^o}$<\/p>\n<p>${W_g} = mg(2l)( &#8211; 1) = &#8211; 2mgl$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/27-removebg-preview-300x184.png\" alt=\"Diagram showing displacement of pendulum bob from bottom to highest point of circle\">\n\n<h3>Work Done by the Electric Field (Without Calculus)<\/h3>\n<p><strong>Ex.:<\/strong> Suppose a particle of mass m and charge q is thrown at a speed u against the direction of uniform electric field E. How much distance will it travel before coming to rest momentarily.<\/p>\n<p><strong>Solution:<\/strong> We can write the electric force experienced by charge q as $E = frac{F}{q}$<\/p>\n<p>$F = qE Rightarrow ma = qE$<\/p>\n<p>$a = frac{{qE}}{m}$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/28-removebg-preview-300x49.png\" alt=\"Diagram of charged particle moving against uniform electric field E\">\n<p>Since the magnitude of the acceleration is constant, the projected particle is moving along a straight line.<\/p>\n<p>Therefore, we can use ${v^2} = {u^2} + 2as$<\/p>\n<p>$0 = {u^2} + 2left( { &#8211; frac{{qE}}{m}} right)(s)$ (negative sign shows that velocity and acceleration have opposite sign)<\/p>\n<p>$frac{{2qE}}{m}s = {u^2}$<\/p>\n<p>$s = frac{{m{u^2}}}{{2qE}}$<\/p>\n<p>Now, we can find the work done by the electric field as<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/29-removebg-preview-300x65.png\" alt=\"Equation for work done by electric field on charged particle\">\n<p>$W = {{bf{F}}_{el}} cdot s$<\/p>\n<p>${W_{el}} = qE cdot scos {180^o}$<\/p>\n<p>${W_{el}} = cdot frac{{m{u^2}}}{{2}}( &#8211; 1)$<\/p>\n<p>${W_{el}} = left( { &#8211; frac{{m{u^2}}}{2}} right)$<\/p>\n\n<h3>Work Done to Move a Charge by External Force and Work Done by an Electric Field (Example With Calculus)<\/h3>\n<p>Let a positive charge Q be kept fixed, and a negative charge (-q) is moved away slowly with the help of external force. We have to calculate work done by external force as (-q) charge particle changes its position from $r = {r_i}$ to $r = {r_f}$. Also, calculate work done by the electric field.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/30-removebg-preview-300x175.png\" alt=\"Diagram showing positive charge Q fixed and negative charge moved along x-axis by external force\">\n<p>Since charge particle (-q) is slowly moving along the x-axis, $left| {{{bf{F}}_{ext}}} right| = parallel left| {{{bf{F}}_{el}}} right|$<\/p>\n<p>Therefore, work done by external agent $d{W_{ext}} = {{bf{F}}_{ext}} cdot {bf{d}}r = {F_{el}} cdot (dr)cos {0^o} = frac{{kQq}}{{{r^2}}}(dr)$<\/p>\n<p>${W_{ext}} = kQqintlimits_{{r_i}}^{{r_f}} {{r^{ &#8211; 2}}(dr)} $<\/p>\n<p>${W_{ext}} = kQqleft[ {frac{{{r^{ &#8211; 2 + 1}}}}{{ &#8211; 1}}} right]_{{r_i}}^{{r_f}}$<\/p>\n<p>${W_{ext}} = &#8211; kQqleft[ {frac{1}{{{r_f}}} &#8211; frac{1}{{{r_i}}}} right]$<\/p>\n<p>$ Rightarrow {W_{ext}} = kQqleft[ {frac{1}{{{r_i}}} &#8211; frac{1}{{{r_f}}}} right]$<\/p>\n<p>Again, as we know from the work-energy theorem for a system of particles:<\/p>\n<p>${({k_f})_{sy}} &#8211; {({k_i})_{sy}} = {W_{{mathop{rm int}} }} + {W_{ext}}$<\/p>\n<p>$ Rightarrow 0 = {W_{el}} + {W_{ext}}$<\/p>\n<p>Therefore work done by the electric field is equal to the negative of work done by external force in this situation.<\/p>\n\n<h2>Work Done in Thermodynamics<\/h2>\n<p>Thermodynamics is a branch of science that deals with the exchange of heat energy between bodies and the conversion of heat energy into mechanical energy and vice-versa.<\/p>\n<p>When a gas expands, then for an infinitesimally small change in volume dV, small work done dW = PdV. Here P is almost constant.<\/p>\n<p>dW = PdV = Area of narrow strip as shown in figure.<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/1-removebg-preview-1-1-300x183.png\" alt=\"P-V diagram showing narrow strip area representing small work done dW during gas expansion\">\n<p>If the volume changes from ${V_1}$ to ${V_2}$ then the total work done by the system:<\/p>\n\n<h3>$W = intlimits_{{V_1}}^{{V_2}} {P(dV)} $ = Area under P-V curve<\/h3>\n<p><em><strong>The area under the P\u2013V graph equals external work done during the process.<\/strong><\/em><\/p>\n<p>Examples:<\/p>\n<p>(i) A refrigerator works isothermally. A set of changes occur in the refrigerator&#8217;s mechanism, but the temperature inside always remains constant. Here, the heat energy is removed and transmitted to the surrounding environment.<\/p>\n<p>(ii) Another example of thermodynamics is the heat pump. The heat is either removed from the house and dumped outside, or the heat is brought inside the house from outside to warm the house. In either case, the purpose is to keep the house at the desired temperature.<\/p>\n\n<h3>Work Done by the System or Work Done on the System<\/h3>\n<p>If the work is done by the system, the volume of gas increases, then the work done is said to be positive.<\/p>\n<p>$left( {{V_f} &#8211; {V_i}} right) &gt; 0$<\/p>\n<p>or, $dV &gt; 0$<\/p>\n<p>i.e., $dW &gt; 0$<\/p>\n<p>If the work is done on the system, then the volume of gas decreases.<\/p>\n<p>$left( {{V_f} &#8211; {V_i}} right) &lt; 0$<\/p>\n<p>or, $dV &lt; 0$<\/p>\n<p>i.e., $dW &lt; 0$<\/p>\n\n<h3>Work Done in Case of Isothermal Process<\/h3>\n<p>In this process, the pressure and volume of gas change, but the gas temperature remains constant.<\/p>\n<p>Here, dT = 0, dU = 0<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/2-300x215.png\" alt=\"P-V diagram showing isothermal process curve at constant temperature\">\n<p>Work done by the gas in the Isothermal process:<\/p>\n<p>$W = left{ {begin{array}{*{20}{c}} {P(dV)}\\ {,,frac{{nRT}}{V}(dV)} end{array}} right.$<\/p>\n<p>Using PV = nRT (Ideal gas equation):<\/p>\n<p>$W = nRTintlimits_{{V_i}}^{{V_f}} {frac{1}{V}left( {dv} right)} $<\/p>\n<p>$W = nRTleft[ {lnV} right]_{{V_i}}^{{V_f}}$<\/p>\n<p>$W = nRTleft( {lnfrac{{{V_f}}}{{{V_i}}}} right)$<\/p>\n<p>or, $W = nRT cdot left( {2.303;{{log }_{10}}left( {frac{{{V_f}}}{{{V_i}}}} right)} right)$<\/p>\n<p>or, $W = nRT cdot left( {2.303;{{log }_{10}}frac{{{P_f}}}{{{P_i}}}} right)$<\/p>\n<p>Here, W is work done during the isothermal change at temperature T for n moles of gas.<\/p>\n<p>An Isothermal process is ideal. In nature, no process is perfectly isothermal. But we can say that melting ice and boiling water are approximately isothermal.<\/p>\n\n<h3>Work Done in Case of Adiabatic Process<\/h3>\n<p>The pressure, volume, and temperature of a gas in an adiabatic process change, but total heat remains constant.<\/p>\n<p>Q = Const, dQ = 0<\/p>\n<p>There should not be any exchange of heat between the system and surroundings. This is a quick process and the internal energy changes as temperature changes.<\/p>\n<p>In the adiabatic process, P, V, and T are related as:<\/p>\n<p>(i) $P{V^gamma } = {rm{constant}}$ (ii) $T{V^{gamma &#8211; 1}} = {rm{constant}}$ (iii) ${P^{1 &#8211; gamma }}{T^gamma } = {rm{constant}}$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/3-removebg-preview-1-1-300x222.png\" alt=\"P-V diagram showing adiabatic process curve steeper than isothermal curve\">\n<p>The work done by the system during the adiabatic expansion is:<\/p>\n<p>${W_{ad}} = intlimits_{{V_i}}^{{V_f}} {Pleft( {dV} right)} $<\/p>\n<p>${W_{ad}} = intlimits_{{V_i}}^{{V_f}} {frac{C}{{{V^gamma }}}left( {dV} right)} $<\/p>\n<p>Here, C is a constant and we can write ${P_i}{V_i}^gamma = {P_f}{V_f}^gamma = C$<\/p>\n<p>${W_{ad}} = Cintlimits_{{V_i}}^{{V_f}} {{V^{ &#8211; gamma }}left( {dV} right) = Cleft( {frac{{{V^{ &#8211; gamma + 1}}}}{{ &#8211; gamma + 1}}} right)_{{V_i}}^{{V_f}}} $<\/p>\n<p>${W_{ad}} = Cleft[ {frac{{{V^{1 &#8211; gamma }}}}{{1 &#8211; gamma }}} right]_{{V_i}}^{{V_f}} = frac{{CV_f^{1 &#8211; gamma } &#8211; CV_i^{1 &#8211; gamma }}}{{1 &#8211; gamma }}$<\/p>\n<p>${W_{ad}} = left[ {frac{{{P_f}V_f^gamma V_f^{1 &#8211; gamma } &#8211; {P_i}V_i^gamma V_i^{1 &#8211; gamma }}}{{left( {1 &#8211; gamma } right)}}} right]$<\/p>\n<p>${W_{ad}} = frac{{{P_i}{V_i} &#8211; {P_f}{V_f}}}{{left( {gamma &#8211; 1} right)}}$<\/p>\n<p>Here $gamma $ is the ratio of molar heat capacity of gas at constant pressure and molar heat capacity at constant volume.<\/p>\n<p>It takes place in a non-conducting vessel. Hence no exchange of heat takes place between the system and its surroundings.<\/p>\n<p>An adiabatic expansion causes cooling and compression causing heating (dV = \u2013 dW).<\/p>\n<p><strong>Example of adiabatic process:<\/strong> Sudden bursting of a tube of a bicycle tire, propagation of sound in gases.<\/p>\n\n<h3>Work Done in Case of Isobaric Process<\/h3>\n<p>It is a process in which the pressure of the system remains constant, i.e., $Delta P = 0 Rightarrow {P_i} = {P_f}$<\/p>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/4-removebg-preview-1-1-300x216.png\" alt=\"P-V diagram showing isobaric process as a horizontal line at constant pressure\">\n<p>So, work done in an Isobaric process is:<\/p>\n<p>$W = intlimits_{{V_i}}^{{V_f}} {Pleft( {dV} right) = Pintlimits_{{V_i}}^{{V_f}} {left( {dV} right)} } $<\/p>\n<p>${W_{text{Isobaric process}}} = Pleft( {{V_f} &#8211; {V_i}} right)$<\/p>\n\n<h3>Work Done in Case of Free Expansion<\/h3>\n<img class=\"lazyload\" decoding=\"async\" src=\"data:image\/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==\" data-orig-src=\"https:\/\/myengineeringbuddy.com\/wp-content\/uploads\/2022\/06\/5-removebg-preview-1-1-300x103.png\" alt=\"Diagram of insulated cylinder with piston separating ideal gas from vacuum for free expansion\">\n<p>The figure shows an insulated cylinder divided into two parts by a thin massless fixed piston. The volume of the left compartment gets filled with an ideal gas, and the right compartment is a vacuum. If we release the piston, gas fills the whole space of the cylinder rapidly. In this expansion, no heat is supplied to the gas as the walls are insulated.<\/p>\n<p>$Delta Q = 0$, as the piston is fixed, no work is done by the gas, $Delta W = 0$<\/p>\n<p>Therefore, internal energy remains constant.<\/p>\n<p>$Delta U = 0,;,,T:{rm{constant}}$<\/p>\n<p>We call such an expansion free expansion.<\/p>\n<p>Related: <a href=\"https:\/\/www.myengineeringbuddy.com\/newtons-laws-of-motion\/\">Newtons laws of motion<\/a> | <a href=\"https:\/\/www.myengineeringbuddy.com\/collisions\/\">Collisions<\/a> | <a href=\"https:\/\/www.myengineeringbuddy.com\/homework-help\/physics-homework-help\/\">Physics Homework Help<\/a> | <a href=\"https:\/\/www.myengineeringbuddy.com\/online-tutoring\/online-physics-tutor\/\">Physics Tutor Online<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>What is Work Done in Physics? Work done in Physics  [&#8230;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-11287","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/www.myengineeringbuddy.com\/blog\/wp-json\/wp\/v2\/posts\/11287","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.myengineeringbuddy.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.myengineeringbuddy.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.myengineeringbuddy.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.myengineeringbuddy.com\/blog\/wp-json\/wp\/v2\/comments?post=11287"}],"version-history":[{"count":0,"href":"https:\/\/www.myengineeringbuddy.com\/blog\/wp-json\/wp\/v2\/posts\/11287\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.myengineeringbuddy.com\/blog\/wp-json\/wp\/v2\/media?parent=11287"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.myengineeringbuddy.com\/blog\/wp-json\/wp\/v2\/categories?post=11287"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.myengineeringbuddy.com\/blog\/wp-json\/wp\/v2\/tags?post=11287"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}