Physics PDF: Distance and Displacement

Stationa objects TREE.-,8 HOUSE A moving car. d:iil. After five seconds car reaches here The position of movinq car changes with time. So, the car is in motion. position A in front of a house and a tree at a particuiar time (In this case, the house and tree are the stationary objects which are taken...

Stationa objects TREE.-,8 HOUSE A moving car. d:iil. After five seconds car reaches here The position of movinq car changes with time. So, the car is in motion. position A in front of a house and a tree at a particuiar time (In this case, the house and tree are the stationary objects which are taken as a reference point). Now, after 5 seconds, we see the same car at position B which is quite far away from the house and the tree (see Figure 2). In Figure 2 we see a car at This means that the position of this car is changing continuously with respect to a stationary object, house or tree. So, we say that this car is moving or that this car is in motion. Some other bodies (or objects) around us which show different kinds of motion are: swing (jhoola), merr\'-go-round, pendulum of a clock, and hands of a watch. If a body moves fairly fast, then its movement (or motion) can be observed easily. But if a body moves very slowly then it becomes difficult to observe its movement immediately. For example, a wrist watch has three hands: a seconds'hand, a minutes'hand and an hours' hand, rvhich move round and round on the dial of the watch. Now; the seconds' hand of a watch moves quite fast, so we can observe the movement (or motion) of the seconds' hand of the watch very easily. But the minutes' hand and hours' hand of a watch move quite slowly, so their movement cannot be observed easil1,. We will have to keep on observing the position of minutes' hand and hours' hand for quite some time to find out t hether they are moving or not. This is because lvhen a body moves, its position changes with time. In order to study the motion of bodies (or objects), we should first know the meanings of two terms: distance and displacement. These are discussed below. Another point to be noted is that in the study of motion, ivhether we use the term 'body' br bbject] it means the same thing. @ I B In er.en-dar language, the words distance and displacement are used in the sane sense but in physics these two words have different meanins: i.et us understand this difference by taking ^/.^\'V t./ 4 / // 3km an example. A (Figure 3) and he has to reach +. Az another place C but first le has to meet his friend living at place 4km l4:Displacement ----, B. Now, the man starts from point A and travels a distance of 5 Distance travelled = 5 + 3 = 8 km km to reach B, and then trar els another 3 km from B to reach C. Displacement = 4 km towards East. Thus, the man goes along the path ABC (shown by dotted trines). Length of the path ABC gives us t].ie actual distance travelled by the man. Thus, the distance travelled by a body is the actual length of the path covered by a moving body irrespective of the direction irt u hich the body travels. For example, in this case, the actual length of the path covered by the man is 5 l,:r - 3 km = B km, so the distance travelled bv the man is B km. Suppose a man live-. at place r0 IVotion