[Music] how do we know whether an object in motion is traveling faster or slower than another object consider two objects object one and object to both moving along the same path just by looking at their motion can you tell me which one of them is moving faster clearly this one is moving faster in comparison to object one object two keeps lagging behind hence we say that the speed of object one is more than the speed of object two speed is that physical quantity which tells us how fast something is moving how do we define it in order to know the speed of an object there are just two things we need to know first the distance traveled by an object in motion and second the time it takes to complete that distance consider a car moving on a straight road first of all can you tell the type of motion its undergoing since it's moving in a straight line it's in a rectilinear motion suppose the time it takes to reach the other side is 30 seconds now consider another car which is similar to the first one it's also moving in a straight line path adjacent to the first one the time taken by this red car to cover the same length of the road is 40 seconds the blue car covered the path length in 30 seconds while the red car covered the same path length in 40 seconds which one of them was moving with greater speed by intuition we can say that the blue colored car was traveling at a greater speed than the red one why because the blue car covered the same distance in lesser time let the length of this path be 420 meters this pot length is nothing but the distance that the car travels in a given amount of time now for each object if we take the ratio of the total distance covered and the time required to cover that distance we will get this this ratio is called the speed of the object yes speed is distance over time since this ratio is greater than this one it means that the blue car traveled with greater speed let's bring in a third car which covers the same distance in 20 seconds so what does it speed then the speed is 420 meters over 20 seconds which will give us 21 meters per second and you can see that this ratio is the greatest of all now I want you to look at the unit's meters per second is one of the units of speed there are many such units of speed that you must be aware of for example kilometers per hour miles per hour feet per minute and so on we will discuss more about these units enough future videos let's discuss something interesting now look at the example of one of the cars the car a the only information I gave you was that it covers 420 meters in 30 seconds that gave us the speed as 14 meters per second I want you to answer the next question I'm asking you in this example can we say that the speed of the car a is constant throughout this distance R we say that the car is covering 14 meters every second through off the path no that's not what we're implying because maybe the car is moving at a really fast speed initially and that it slows down in the middle and then stops and then again speeds up so this beat does not imply that the speed is constant at 14 meters per second throughout so what is the speed then the speed we calculated here is the average speed in fact in all the three examples it was average speed how do we define it average speed is defined as the total distance traveled by an object divided by the total time taken we will continue to discuss more about average speed in our next video [Music] you