Page 1 : 2, , a, , , , a, Eo :, , & p, in day-to-day life. For each of these, activities, ask the following questions, and answer them, @ What is the work being done on?, , (t) What is happening to the object?, {it) Who (what) is doing the work?, |.2 Sc, , TENTIFIC CONCEPTION OF WORK, inderstand the w., , ay we view work and, t€ Work from the, , point of view of science,, S consider some situations:, , ush a pebble lying on a surface. The, le moves through a distance. You exerted, ce on the pebble and the pebble got, ced. In this situation work is done., girl pulls a trolley and the trolley moves, sh a distance. The girl has exerted a, on the trolley and it is: displaced., ore, work is done., , a book through a height. To do this, ist apply a force. The book rises up., , s a force applied on the book and the ., , is moved. Hence, work is done., oser look at the above situations, that two conditions need to be, for work to be done: (i) a force should, a object, and (ii) the object must be, 1., , one of the above conditions does, work is not done. This is the way, ork in science., , ock is pulling a cart. The cart, ere is a force on the cart and the, 10ved. Do you think that work is, is situation?, , 11.2, , f some situations from your, fe involving work., , , , with your friends whether, ing done in each situation., son out your response., done, which is the force acting, ject? of, the object on which the work, ?, lappens to the object on which, done?, , , , , , Activity 11.3, | Think of situations when the ¢, not displaced tn spite of a fe Hag. ed, note acting, Also think of situations w), , hen an object, , gets displaced in the absence of a fore,, Pe, , acting on it., List all the situations that, , think of for each, you can, Discuss with your fry, work is done in these g;, , Be, , lends whether, ituations,, , 11.1.3 WORK DONE BY A CoNsTany FORCE, , How is work defined in, understand this, we shall firs, case when the force is acting i, of displacement., , Let a constant force,, Let the object be dis, distance, s in the direction of the force (Fig., 11.1). Let Wbe the work done. We define work, to be equal to the product of the force and, displacement. ‘, , Work done = force x displacement, , W =Fs, , Science? To, it consider the, in the direction, , F act on an object., placed through a, , , , (11.1), , , , Fig. 11.1, , Thus, work done by a force acting on an, object is equal to the magnitude of the force, multiplied by the distance moved in the, direction of the force. Work has only, magnitude and no direction., , In Eq. (11.1), if F= 1 Nand s= 1m then, the work done by the force will be 1 N m, Here the unit of work is newton metre (N m, or joule (J). Thus 1 J is the amount of worl, , 147