Just because you see something in a movie, doesn’t mean you should try it yourself. Consider, for example, a man running on top of a moving train. First, you can’t be sure it’s true. In early westerns, they used moving backgrounds to make the fake trains appear to be in motion. Now there is CGI. Or they might speed up the film to make the real train look faster than it actually is.
So here’s a question for you: Really? possible Running on the roof of a train and jumping from one car to another? Or does a train speed ahead of you while you’re in the air so that you land right where you took off? Or worse, will you fall between cars as the gap moves forward, extending the distance you have to travel? That, my friends, is why stuntmen study physics.
formulate action
What exactly is physics? Basically, it’s a set of real-world models that we can use to calculate forces and predict how an object’s position and velocity will change. However, without a reference frame, we cannot find the position or velocity of any object.
Suppose I’m standing in a room with a ball in my hand, and I want to describe its location. I can use Cartesian coordinates in 3D space to give the ball (x, y, z) values. But these numbers depend on the origin and direction of my axis. It seems natural to use a corner of the room as the origin, with the x and y axes running along the bottom of two adjacent walls and the z axis running vertically upward. Using this system (in meters) I find that the ball is at point (1, 1, 1).
What if my friend Bob was there, and he measured the ball’s position differently? Maybe he puts the origin of the ball’s start in my hand and gives it an initial position (0,0,0). This also seems logical. We can argue about who is right, but that is foolish. We just have different frames of reference, and they’re all arbitrary. (Don’t worry, we’ll get back on the train.)
Now I throw the ball straight into the air. After a short interval of 0.1 seconds, my coordinate system places the ball at (1, 1, 2), which means it is 1 meter higher. Bob also has a new position (0, 0, 1). But note that in both systems the ball rises 1 meter in the z direction. So we agree that the upward velocity of the ball is 10 meters per second.
Moving frame of reference
Now imagine I take this ball on a train traveling at 10 meters per second (22.4 miles per hour). I throw the ball straight up again – what happens? I’m inside a train car, so I’m using a coordinate system that moves with the train. In this moving frame of reference, I am stationary. Bob is standing on one side of the track (he can see the ball through the window), so he uses a stationary coordinate system and I move in it.
Provided by Rhett Alan