2 ms·

My physics teacher was really good with this stuff. He put things into context. This example is not true, however, this example is true enough to teach you xyz.

My physics teacher was really good with this stuff. He put things into context. This example is not true, however, this example is true enough to teach you xyz. He suggested that part of continuing on to higher forms of physics study meant that a lot of these older concepts had to be beaten out of you, and his preference was largely not to rely/solidify them as concepts so it wouldnt take as much energy to remove them later. We were encouraged to find ways to break these examples too, if we could, which was rare, and on some occasions he would stay back to demonstrate how they were false after class.

WalterBright 2y ago
I used to believe that a baseball kept accelerating after it left my hand in a throw. It was a major reorienting for me to learn differently.
- gravescale 2y ago
  In the relativistic inertial frame of the thrown baseball, it'll not be accelerating, at first. But it will be accelerating at 9.81m/s² (along with the Earth's surface, and hopefully you) after it lands and is just sitting there. The inertial frame will have continued along its original geodesic into the ground, though (or rather, the frame is only instantaneously defined at the moment of the release, but the ball would have followed that path). If you can convince the ball to continue to not-accelerate indefinitely, NASA or Vought International may have a job for you. In the Newtonian inertial frame of the "stationary" Earth, it accelerates downwards at 9.81m/s² until it hits the floor and comes to a stop and is no longer accelerating ("gravity", which is a thing here, and the normal force now summing to zero). This is fairly academic for sporting goods, as if working with these two frames results in substantially different outcomes for you or your ball, your day is probably going badly, or at least fairly energetically, and baseball isn't your priority right now.

WalterBright 2y ago

I used to believe that a baseball kept accelerating after it left my hand in a throw. It was a major reorienting for me to learn differently.

gravescale 2y ago
In the relativistic inertial frame of the thrown baseball, it'll not be accelerating, at first. But it will be accelerating at 9.81m/s² (along with the Earth's surface, and hopefully you) after it lands and is just sitting there. The inertial frame will have continued along its original geodesic into the ground, though (or rather, the frame is only instantaneously defined at the moment of the release, but the ball would have followed that path). If you can convince the ball to continue to not-accelerate indefinitely, NASA or Vought International may have a job for you. In the Newtonian inertial frame of the "stationary" Earth, it accelerates downwards at 9.81m/s² until it hits the floor and comes to a stop and is no longer accelerating ("gravity", which is a thing here, and the normal force now summing to zero). This is fairly academic for sporting goods, as if working with these two frames results in substantially different outcomes for you or your ball, your day is probably going badly, or at least fairly energetically, and baseball isn't your priority right now.