Why is inertia/relativity so hard to understand?

Quote from: jroa on April 24, 2014, 09:21:28 AM

If your friends are standing around you, then they are in your location and would experience the same thing that you experience. 

You do understand the meaning of local and outside observer, do you not?

Sure, but the problem is, there's a chance for many different "locals".

Each individual person is a "local" system.

The entire box is a "local system".

What if someone is in a helicopter overhead observing? Then that entire group becomes a "local system"

What if we put the same people in a room, with only cameras recording the outside of the building? Then, to some observing through the camera, the ground in the building should be rising up, until it breaks through the roof?

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

Quote from: jroa on April 24, 2014, 09:53:45 AM

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

So lets go back to the people in/outside the building. If someone jumps in the building, and someone stands outside the building, than the ground needs to be doing something different to "catch up" to the person n the building, because according to you, we're all moving upwards at 9.8 m/s^2

Quote from: RandomREalist on April 24, 2014, 10:07:28 AM

Quote from: jroa on April 24, 2014, 09:53:45 AM

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

So lets go back to the people in/outside the building. If someone jumps in the building, and someone stands outside the building, than the ground needs to be doing something different to "catch up" to the person n the building, because according to you, we're all moving upwards at 9.8 m/s^2

You understand that the Earth is an, at least, semi-solid body, right?

Quote from: th3rm0m3t3r0 on April 24, 2014, 10:08:30 AM

Quote from: RandomREalist on April 24, 2014, 10:07:28 AM

Quote from: jroa on April 24, 2014, 09:53:45 AM

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

So lets go back to the people in/outside the building. If someone jumps in the building, and someone stands outside the building, than the ground needs to be doing something different to "catch up" to the person n the building, because according to you, we're all moving upwards at 9.8 m/s^2

You understand that the Earth is an, at least, semi-solid body, right?

Yep, which to me, implies that this upward movement to catch up to someone jumping shouldn't be possible

Quote from: RandomREalist on April 24, 2014, 10:13:45 AM

Quote from: th3rm0m3t3r0 on April 24, 2014, 10:08:30 AM

Quote from: RandomREalist on April 24, 2014, 10:07:28 AM

Quote from: jroa on April 24, 2014, 09:53:45 AM

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

So lets go back to the people in/outside the building. If someone jumps in the building, and someone stands outside the building, than the ground needs to be doing something different to "catch up" to the person n the building, because according to you, we're all moving upwards at 9.8 m/s^2

You understand that the Earth is an, at least, semi-solid body, right?

Yep, which to me, implies that this upward movement to catch up to someone jumping shouldn't be possible

Why?
The Earth is accelerating upwards at 9.81 m/s^2.
When you jump, you are accelerating upwards at a rate a bit faster than this.
That is, until you hit the apex of your jump, then you start decelerating. The deceleration allows for the Earth to catch back up to you. When you're on the ground, you're local to the Earth's acceleration once more.
What's the problem?

Quote from: jroa on April 24, 2014, 09:53:45 AM

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

So lets go back to the people in/outside the building. If someone jumps in the building, and someone stands outside the building, than the ground needs to be doing something different to "catch up" to the person n the building, because according to you, we're all moving upwards at 9.8 m/s^2

Quote from: th3rm0m3t3r0 on April 24, 2014, 10:16:26 AM

Quote from: RandomREalist on April 24, 2014, 10:13:45 AM

Quote from: th3rm0m3t3r0 on April 24, 2014, 10:08:30 AM

Quote from: RandomREalist on April 24, 2014, 10:07:28 AM

Quote from: jroa on April 24, 2014, 09:53:45 AM

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

So lets go back to the people in/outside the building. If someone jumps in the building, and someone stands outside the building, than the ground needs to be doing something different to "catch up" to the person n the building, because according to you, we're all moving upwards at 9.8 m/s^2

You understand that the Earth is an, at least, semi-solid body, right?

Yep, which to me, implies that this upward movement to catch up to someone jumping shouldn't be possible

Why?
The Earth is accelerating upwards at 9.81 m/s^2.
When you jump, you are accelerating upwards at a rate a bit faster than this.
That is, until you hit the apex of your jump, then you start decelerating. The deceleration allows for the Earth to catch back up to you. When you're on the ground, you're local to the Earth's acceleration once more.
What's the problem?

That's not quite accurate.  When you jump, you have a greater acceleration for a small amount of time while you are applying the force to cause the jump.  As soon as you leave the ground, you are traveling at a constant speed. For example, let's assume a 20m/s^2 jump acceleration which is applied over .5 seconds, and round the UA to 10 for simplicity.  You will be traveling 10 m/s faster than the earth as soon as you leave the ground and will continue to travel at this speed
 The earth will continue to accelerate at 10m/s^2 though and well catch your speed at 1 second after you jumped and catch up to you between the 1 and 2 second mark.

Quote from: RandomREalist on April 24, 2014, 10:07:28 AM

Quote from: jroa on April 24, 2014, 09:53:45 AM

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

So lets go back to the people in/outside the building. If someone jumps in the building, and someone stands outside the building, than the ground needs to be doing something different to "catch up" to the person n the building, because according to you, we're all moving upwards at 9.8 m/s^2

You do understand that the Earth is the spaceship in my analogy, right?  Everybody on the Earth has basically the same Frame of Reference.  You would have to be floating in space, watching the Earth wiz by in order to be an outside observer. 

Why do I feel light I am lecturing to a bunch of middle schoolers?

Quote from: jroa on April 24, 2014, 11:04:46 AM

Quote from: RandomREalist on April 24, 2014, 10:07:28 AM

Quote from: jroa on April 24, 2014, 09:53:45 AM

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

So lets go back to the people in/outside the building. If someone jumps in the building, and someone stands outside the building, than the ground needs to be doing something different to "catch up" to the person n the building, because according to you, we're all moving upwards at 9.8 m/s^2

You do understand that the Earth is the spaceship in my analogy, right?  Everybody on the Earth has basically the same Frame of Reference.  You would have to be floating in space, watching the Earth wiz by in order to be an outside observer. 

Why do I feel light I am lecturing to a bunch of middle schoolers?

Maybe you're just not using accurate language, or maybe I'm just not completely focused (if so, apologies, final exam time tends to do that).

Earlier in the thread, you said the earth "speeds up" to meet an object falling. That to me, can lead to  one of a few different scenarios.

1) someone jumps, and the entire fabric of the earth changes speed (faster than the 9.8 that you claim it's constantly moving at) to catch the person. This would lead to everyone else in the world experiencing an unanticipated shift in THEIR acceleration, probably knocking them to the ground.

2) someone jumps, and their immediately local space speeds up to bring them back down. This should result in someone separate from the immediate point of jumping, to visibly see something move up, and possibly create new matter beneath them.

I'm not sure if either of those things make sense, I'm feeling a little punch drunk you might say, but hopefully this will.

Imagine you are at ground level, stationary, and able to fire something perfectly vertically at 9.8 m/s, what would happen? (this isn't a trick question, and I know what you'll say so just think about it)

Now, imagine the same projectile, but this time, you yourself are ALSO sustaining an upward movement of 9.8 m/s^2 (meaning, you are already away from the earth and maintaining distance away from it.) what would happen with the projectile?

Quote from: RandomREalist on April 24, 2014, 12:51:31 PM

Quote from: jroa on April 24, 2014, 11:04:46 AM

Quote from: RandomREalist on April 24, 2014, 10:07:28 AM

Quote from: jroa on April 24, 2014, 09:53:45 AM

If one person is on a spaceship which is accelerating at 9.8 m/s/s and another person is stationary floating in space, the person in the spaceship feels the effects of the acceleration while the person floating in space does not.  This is the difference between local and outside observer.

So lets go back to the people in/outside the building. If someone jumps in the building, and someone stands outside the building, than the ground needs to be doing something different to "catch up" to the person n the building, because according to you, we're all moving upwards at 9.8 m/s^2

You do understand that the Earth is the spaceship in my analogy, right?  Everybody on the Earth has basically the same Frame of Reference.  You would have to be floating in space, watching the Earth wiz by in order to be an outside observer. 

Why do I feel light I am lecturing to a bunch of middle schoolers?

Maybe you're just not using accurate language, or maybe I'm just not completely focused (if so, apologies, final exam time tends to do that).

Earlier in the thread, you said the earth "speeds up" to meet an object falling. That to me, can lead to  one of a few different scenarios.

1) someone jumps, and the entire fabric of the earth changes speed (faster than the 9.8 that you claim it's constantly moving at) to catch the person. This would lead to everyone else in the world experiencing an unanticipated shift in THEIR acceleration, probably knocking them to the ground.

2) someone jumps, and their immediately local space speeds up to bring them back down. This should result in someone separate from the immediate point of jumping, to visibly see something move up, and possibly create new matter beneath them.

I'm not sure if either of those things make sense, I'm feeling a little punch drunk you might say, but hopefully this will.

Imagine you are at ground level, stationary, and able to fire something perfectly vertically at 9.8 m/s, what would happen? (this isn't a trick question, and I know what you'll say so just think about it)

Now, imagine the same projectile, but this time, you yourself are ALSO sustaining an upward movement of 9.8 m/s^2 (meaning, you are already away from the earth and maintaining distance away from it.) what would happen with the projectile?

If by "speed up" you mean accelerate, what is the problem with the Earth accelerating up to a person who has jumped?
The projectile is the same thing as someone jumping, and the same thing would happen.
Refer to DuckDodger's post.

Yes, of course the effect is local.  An outside observer would not experience the same effect.  What is your point?

Read about spaceships approaching the speed of light.  Now, expand your mind and think of the Earth as the space ship.  Everyplace across the Earth is local to every other place.

Tidal forces, and a more precise definition

So far, so simple. Too simple, in fact, in several respects. Strictly speaking, all that was said about the equivalence of gravity and acceleration is true only for gravitational fields that are strictly homogeneous. Only in homogeneous gravitational fields are all bodies - per definition - accelerated in exactly the same way, namely in exactly the same direction and at exactly the same rate; as a result, it is indeed true that a researcher inside a cabin cannot distinguish acceleration from gravity. But real gravitational fields are always to a certain extent inhomogeneous.

Take, for example, the gravitational field of the earth. True, here on the surface, looking at experiments which take up only a very, very small fraction f the total surface area of the earth, the gravitational field is, to good approximation, homogeneous: all objects fall to the floor along parallel paths, in the same direction ("down") and with the same acceleration (at least as long as the effects of air friction can be neglected). But if we look closer, the situation is a bit more complex. Here is an example where the deviations from homogeneity are clearly visible - a truly gigantic elevator which contains two spheres, all falling towards the earth: