 If a coin is dropped from the top of a building and it falls on your head, will it kill you? You might say maybe not. This building is not that tall. Okay, what about this building? If a coin is dropped from a really tall building and it falls on your head, will it kill you? That really is a morbid question, but I'm sure you want to know the answer. So let's get into it. We will zoom into the coin and the coin has its own weight, which is acting downwards. It has some mass. And as the coin falls down, there is a constant acceleration that the coin is falling with, which is acceleration due to gravity that is 10 meters per second square. So as the coin leaves the top of the building, it starts falling down, its velocity keeps on increasing because it is the constant acceleration of 10 meters per second square. And as its velocity increases, as it keeps on falling down, it strikes the air particles, the air particles surrounding it. And as it strikes the air particles, there is a resistive force, which is exerted by the air particles on the coin. And this is, this acts on the upward direction. We can call it air resistance, a form of a friction. We can also call it, we can also call it drag force. Drag force is the force that opposes a body's motion as that body moves through any fluid air or any liquid, any kind of fluid. So, so as the coin is falling down, its velocity is increasing, it is striking the air particles, air particles are providing a resistive force in the upward direction, opposing the motion. Now the coin will not fall with the same acceleration of 10 meters per second square. It will be somewhat less because there is an upward force. But there is still a positive acceleration, which means the velocity will still keep on increasing. Maybe not by the same amount as it was before when the acceleration was 10. Now the acceleration is slightly less, maybe 8 or 9, don't know. But still the velocity will increase because there is a positive acceleration. And velocity are in the same direction, so velocity will increase. And as it falls faster, the air particles and the coin collide with a greater force. So now the air particles exert even a greater resistive force. And as the velocity of the coin further increases, the resistive force also increases. And as it increases some more, the resistive force increases some more, until the point when air resistance is equal to weight. And it is at that point, there is no net force which acts on the coin, sigma f, the net force is zero. And according to the second law, when the net force is zero, there is no acceleration. The coin will move with a constant velocity, with that very velocity. And that velocity is called terminal velocity, which is the maximum speed or the maximum velocity that a falling body reaches. And when the body reaches this terminal velocity, now there is no change in velocity. It is falling with the same velocity. So the force with which the air particles strike the coin, even that doesn't really change. It remains like this, it remains as much equal to the weight. So any object that falls from a height reaches a terminal velocity. It differs from object to object. But for a coin, it's generally between 13 to 22 meters per second. Now this might seem a lot, but a coin is such a light object that it doesn't really have any serious impact on your head. And you do survive if a coin falls on your head because of terminal velocity.