 Hey, welcome friends once again to this problem-solving session in physics We are dealing with the chapter called motion and this particular question deals with Concept of distance and displacement. So let's first read the question and understand what is the demand of the question So it says in a long-distance race. So there is a race going on the elites were expected to take Four rounds. This is the data point four rounds of the track Such that line of finish was same as the line of start Suppose the length of the track was 200 meters. So for your understanding, I have you know shown a small You know diagram here, which is a you know race track So if we consider this full length to be 200, what is the length? So let me draw it here. So if you see this total length Is given to be 200 meters, right? So this length of the track. Let's say D D for 200 meters, right? This is what they have given now what? It said that What is the total distance to be covered by the athletes distance now the question is Total distance distance is nothing but the length of the Track right or the length of the path on which the body moves is called the distance You all know so for example, let's say this is the path of the body body goes from A to B So you know that the length of this path the actual length, isn't it? So you have to take the measure of this Track and then this is distance. So in this case, what is the question? It says that they go four rounds four rounds right four rounds and in one round how much distance does do they cover? So very easy. So in in one You know, so let's say you're talking about point number one here in one round In one round they cover Athletes cover athletes. So we have athletes here. So athletes athletes Athletes, sorry Athletes cover how much? 200 meters D is equal to 200 meters Therefore in four rounds, it's a unitary method question actually in four rounds Four rounds they would cover how many how many meters or how much distance four D So in one round 200 so four four rounds four into 200 That means 800 meters That becomes their distance right so going round and round one two three and four like that, right? so four times they complete the um The track or the or the laps whichever way you want to say it so 800 meter becomes a distance very very easy, isn't it? Now second question says what is the displacement and what is the displacement guys defined in physics? So displacement is nothing but the shortest distance between final and initial position In this case if you if you see the athlete, let's say start from this point goes for one full circle Then again goes for the second one then again goes for the third one and then final fourth one and comes back to the same place So very easy. How what is the displacement clearly? There is you know the final and the initial positions are same so initial and final positions final positions positions are same Hence we know that whenever there is initial and final position same we say Displacement in that case Displacement becomes zero right so there is no gap between the initial and final position There's no distance or no, you know measure between in that you know in terms of length of the final and initial position so final and initial are Coincident points so if there is no You know a displacement between or let's say the body didn't go any displacement undergo any displacement So this is clear now it doesn't depend on the shape of the path actually So whichever is the path you take and you come back to the original point So the final and initial position are same and hence there is no displacement irrespective of the nature of the path You take now is the motion of the athlete uniform or non-uniform. This is the question number three So for that we need to understand what is uniform motion? So uniform motion is uniform motion is a motion in which velocity stays constant What is uniform motion velocity? stays Constant right and what is velocity guys velocity is nothing but speed plus Direction direction speed plus the direction must remain Must stay same Must stay same that is speed should be constant That means it should cover equal distance at in equal interval of time as well as direction should be constant And when is the detection constant when a body actually moves in a straight line motion in a straight line? motion in a straight line can only ensure Motion in a straight line can only ensure uniform motion It doesn't mean that all straight line motions will be uniform. No when you throw something up against the gravity It's a motion in straight line But that's not uniform motion why because the velocity keeps on reducing and finally ends up being zero at the highest point And then it starts going, you know increasing once again, right? So that is also motion in a straight line But that's not uniform motion owing to the changing speed at every moment but if there is there is something which is changing this the direction of Motion every time it cannot be in Uniform motion for example if this is that this is a track and the you know The object is moving across this track It cannot have uniform motion why because at every moment the velocity direction is changing You know that velocity is a scalar quantum vector quantity Sorry, so velocity direction at every point is changing. So when the direction is changing, it cannot be uniform It cannot be same well same velocity. So velocity doesn't stay constant by virtue of what? changing direction so we can write it's not it's not a case of uniform Uniform motion and the reason being Reason is velocity is not constant velocity is not Constant and why is it not constant? because because because athletes athletes change Direction direction While running isn't it while Running then only they are coming back to the same old or initial point hence Not a uniform velocity, right? Not a uniform motion Okay Is the displacement of an athlete and the distance moved by him at the end of the race equal the fourth question? The fourth question is is the displacement of an athlete and the distance moved by him at the end of the race equal? Clearly not why because the distance is can you see 800 meters is already there and what is the displacement zero? So how can zero be equal to 800 meters? So hence we say answer for is clear. No the distance the distance as well as Distance sorry distance is not same as is not Same as Same as displacement Displacement at the end of the race end of the Race and just to add to your knowledge The distance and displacement would be same Only in a straight line motion, right? So and that too in one direction. So what I what do I mean is? So there's a body which goes like that Okay, so in this case only Distance and displacement are same if the body returns back to the same position Then distance and displacement are not same again if the body changes direction Like that while moving then also distance and displacement are Not same. So only criteria is they must be moving in a straight line and that too only in one direction one direction One direction straight line motion Straight line motion in this case. What will happen? They will have distance equal to displacement