 Let's solve a couple of questions on effects of acceleration. So the first one says which of these has the highest magnitude of acceleration. And there is a note which says assume a constant direction of motion. Okay. So the direction is not changing. It's, we can say it's moving in the same direction. We have to choose one answer out of these three options. Why don't you pause the video, read the options and first try this one on your own. All right. Hopefully we have given this a shot. So the first one says a plane flying at 400 kilometers per hour for five seconds. Now we need to figure out the highest magnitude of acceleration. And for that we need to know what acceleration is. We know that acceleration, this is, this is the rate of change of velocity. How quickly or how slowly the velocity is changing. We can write this, we can write it in this manner. This is change in velocity, change in velocity divided by, divided by time taken. This is your time interval. So for the first one, we aren't really seeing any change in velocity as such. The plane is moving with one, with one velocity, 400 kilometers per hour. So there is no change in velocity. So there is no acceleration. So this one is wrong. In the second one, it says a ball rolling downhill while its speed changes from 30 kilometers per hour to 40 kilometers per hour in five seconds. Okay. So here there is some change in speed. And if the direction is constant, this can be written as change in speed as well, because velocity is just speed with direction. So if the direction is not changing, velocity is just speed. Now ball rolling downhill speed is changing from 30 to 40. So let's see what the change in speed is. That would be 40 minus 30, 40 kilometers per hour minus 30 kilometers per hour. So 10 kilometers per hour, that is the change in speed. And this is happening in five seconds. This is happening in five seconds. In five seconds, the change is 10 kilometers per hour. So we can say that in one second, the change would be two kilometers per hour. So the acceleration is two kilometers per hour per second, that is the acceleration. For the third one, third one says a mouse moving uphill while its speed changes from 10 to 15 kilometers per hour in two seconds. So here the change in speed, that is five kilometers per hour. And this is happening, this is happening in two seconds. In two seconds, the change is five kilometers per hour. So in one second, we can say that the change would be 2.5 kilometers per hour. So the acceleration here is 2.5 kilometers per hour per second. We can say that in one second, the speed increased by 2.5 kilometers per hour. But over here in one second, the speed increased by two kilometers per hour. So we can see that the acceleration, it's highest for option C. The magnitude of acceleration is more for option C. And this also tells us one interesting thing which is that it's not necessary that high velocity means high acceleration. It's not always true. Because we need to really see what is the change in velocity. For instance, in option B, we can see that the velocity, it's going from 30 to 40, it's going to a higher velocity compared to at least 15. But still the acceleration in option B is less because the change in velocity, how quickly that speed of velocity changed, that was lower compared to option C. All right, now let's move on to the next question. A car is accelerating. Which of these is necessarily changing for the car? We have to choose one option out of these four options. Again pause the video, give this one a try. All right, again hopefully we have given this a shot. Now the case is just saying that a car is accelerating. That's all that it says. And we need to think about whether or not the speed is changing for this car. So let's try to think about this. What does it mean that a car is accelerating? First, what does accelerating even mean? This is change in velocity that is delta v, change in velocity per unit time. And what was velocity to begin with? Velocity, velocity was speed, speed with a direction. There was magnitude and there was direction. So for an object's velocity to change, either the speed can change, either the magnitude with which it is moving, either that can change or the direction can change. For example, think about an object moving with a constant speed in a circle. Object moving in a constant speed in a circle. Here the magnitude of velocity that is not changing. But the direction is constantly changing. So in this case we can say that there is a change in velocity because even though the speed or the magnitude that's not changing. But the direction is. So even this is a case of change in velocity and even in this case there will be some acceleration. So option A is actually not right because it's not necessary that the speed has to change. Even the direction, only the direction can change and even then there will be a change in velocity and an acceleration. And by similar logic we can say that even option B is wrong because again we can have an object moving in the same direction but with increasing speed. With increasing speed. Now the direction is not changing but the speed is changing which means again the velocity is changing because velocity is both speed and direction. So even here there will be some acceleration. Option B is wrong. Option C says either speed or direction which is right because that is those are the cases that we discussed. For an object to have a change in velocity either the speed or the direction can change. Any one of them can change and there will be a change in velocity. Both of them can also change, there will be a change in velocity. So option C is it's right. And option D says both speed and direction. Now again the question is asking necessarily changing, necessarily. So it's not necessary that the object has both of these quantities changing. Anyone can change and there will be a change in velocity. So even option D, this is wrong, this is wrong. It's not necessary that both speed and direction has to change. Only one changes and there is a change in velocity and there is an acceleration.