Quote:
Originally Posted by CCuster_911
And you think a car is sealed from the outside world when the widows are up? Wouldn't we be in danger of running out breathable air?
Well, he is making a fair point but he doesn't understand why he's making it.
My top of train example was bad, let's take the ball inside of the train for a second.
Let's assume the train has a constant velocity, meaning it is neither in the process of accelerating or decelerating. When I sit in the train seat with my ball or whatever, my ABSOLUTE position is increasing with respect to the ground and is a function of my horizontal velocity - meaning, whatever speed (actually velocity, velocity and speed aren't the same thing) the train is going, my ass on the seat is also going.
However, my position relative to the rest of the train car remains unchanged, because we are all traveling at the same velocity as the train.
Ok. So I throw the ball directly upwards at a 90 degree angle into the air, applying vertical force to the ball. It still carries the HORIZONTAL velocity of the train, but it now has a vertical velocity as well, and a force is being applied to it, namely my hand and then gravity forcing it back down. However, no horizontal force whatsoever is being applied to the ball, so it maintains its horizontal velocity (thus its relative position to the rest of the train car) and lands in the same spot as it left, with respect the rest of the car.
Now take the ball outside and throw it into the air. It now has horizontal forces being applied to it, namely, drag caused by the air, which will cause it to decelerate with respect to the train's constant velocity.
Keep in mind, the train is experiencing the same force, drag - but it is self powered and able to maintain a constant velocity. That is why your balloon drifts off. Take the same balloon and let it loose inside of the train and it will go straight up.
Now, think of the airplane as the ball, the atmosphere as the train car, and the earth as the train. Except there's even more advantage for the plane, because it is self powered and able to change its relative position to the earth's surface at will.