Physics Question

[ErikFinn]

this is basic high school physics, but it was so long time ago...
but I guess as long as there is no acceleration then it's the same..?

[DefinitelyMe]

Originally Posted by ErikFinn

this is basic high school physics, but it was so long time ago...
but I guess as long as there is no acceleration then it's the same..?

Yes, it is. See post #36, which took me forever to write but it seems was too long for people to read :-( The feeling of despair is overwhelming!

[ErikFinn]

Originally Posted by DefinitelyMe

Yes, it is. See post #36, which took me forever to write but it seems was too long for people to read :-( The feeling of despair is overwhelming!

I admit, I'm quilty. Not just dumb but lazy as well as I only read the first page partially..

[onestepcsy37]

If you began climbing the steps inside the rocket while it was on the ground and continued climbing as it rose into space you would need less energy with each step as earths gravitational pull would become less and less of a factor.

Or did someone already mention this?

[Stu Jackson]

Originally Posted by onestepcsy37

If you began climbing the steps inside the rocket while it was on the ground and continued climbing as it rose into space you would need less energy with each step as earths gravitational pull would become less and less of a factor.

Or did someone already mention this?

Not during the acceleration phase you wouldn't.

[Adelie]

Originally Posted by onestepcsy37

If you began climbing the steps inside the rocket while it was on the ground and continued climbing as it rose into space you would need less energy with each step as earths gravitational pull would become less and less of a factor.

Or did someone already mention this?

Provided the rocket maintained the same net acceleration the energy expended would be the same, since once again you are moving the in the frame of reference of the rocket.

Madness I tell you madness lies down this road.

[Stu Jackson]

Originally Posted by Adelie

Provided the rocket maintained the same net acceleration the energy expended would be the same, since once again you are moving the in the frame of reference of the rocket.

The "madness" is the misunderstanding of the differences between velocity and acceleration.

[onestepcsy37]

Ok, like the song says, you guys are blinding me with science. So I will pose a question and maybe your answer will help me envision this better.

1. I am in a rocket way out in space. The rocket is neither accelerating or decelerating.
2. I am in a rocket way out in space. The rocket is accelerating.

Question. Assuming there is no gravitational force present, does one of these situations require more effort for me to move about inside the rocket?

[Adelie]

Originally Posted by onestepcsy37

Ok, like the song says, you guys are blinding me with science. So I will pose a question and maybe your answer will help me envision this better.

1. I am in a rocket way out in space. The rocket is neither accelerating or decelerating.
2. I am in a rocket way out in space. The rocket is accelerating.

Question. Assuming there is no gravitational force present, does one of these situations require more effort for me to move about inside the rocket?

1) would take very little effort depending on how fast you wanted to move thru the space craft. If there was no air inside and were content to move extremely slowly effort would approach zero.

2) would with require significantly more effort than 1) if in vacume or filled with air; or none at all depending on where in the space craft you wanted to go. If you wanted to go in the opposite direction from acceleration then no effort is involved, let go of what is supporting you and no effort is required to move relative to the space craft. Might be painful when you get to where you want to be in the craft depending on rate of acceleration.

If the spacecraft is filled with water and you are weighted for neutral buoyancy then any direction of movement will require very little effort if speed through the spacecraft is kept very very low.

[Stu Jackson]

Originally Posted by onestepcsy37

Ok, like the song says, you guys are blinding me with science. So I will pose a question and maybe your answer will help me envision this better.

1. I am in a rocket way out in space. The rocket is neither accelerating or decelerating.
2. I am in a rocket way out in space. The rocket is accelerating.

Question. Assuming there is no gravitational force present, does one of these situations require more effort for me to move about inside the rocket?

Good question. Let's assume that since you are "in a rocket way out in space" that you are alive and well, no vacuum, no water surrounding you. Kinda like Captain Kirk and the crew on the Enterprise, right?

Case 1 - constant velocity - just like walking around at home.

Case 2 - changing velocity - just like trying to walk in an airplane that's taking off - it'd be harder.

For the "science" challenged, or those who forgot high school physics : acceleration is a change in veolocity.

[Adelie]

Originally Posted by Stu Jackson

Good question. Let's assume that since you are "in a rocket way out in space" that you are alive and well, no vacuum, no water surrounding you. Kinda like Captain Kirk and the crew on the Enterprise, right?

Case 1 - constant velocity - just like walking around at home.

Case 2 - changing velocity - just like trying to walk in an airplane that's taking off - it'd be harder.

For the "science" challenged, or those who forgot high school physics : acceleration is a change in veolocity.

Try again on case 1. Givens are
A. Constant velocity
B. Away from any gravitational influence.

So you would be weightless in the craft and movement would involve floating with comparatively little effort. Walking around wouldn't happen without magnetic or Velcro footwear which would involve extra effort picking each foot up for the next step.


I paid attention in college physics. Kinematic and gravitational acceleration are functionally indistinguishable when considering primary effects. By looking at tidal effects or standing in a remote frame of reference you can distinguish them.

[TeddyDiver]

Originally Posted by Adelie

.
So you would be weightless in the craft

Can you prove that? All objects with a mass have gravitational pull between each other. For the sake of "simplicity" lets assume the craft is a sphere and the hull has constant thickness and density.

Ps. A looong time ago when I was in highschool this question popped in to my mind in the middle of booooring lesson. Anyway had something to do next week solving it..

[Stu Jackson]

Originally Posted by Adelie

Try again on case 1. Givens are
A. Constant velocity
B. Away from any gravitational influence.

So you would be weightless in the craft and movement would involve floating with comparatively little effort. Walking around wouldn't happen without magnetic or Velcro footwear which would involve extra effort picking each foot up for the next step.


I paid attention in college physics. Kinematic and gravitational acceleration are functionally indistinguishable when considering primary effects. By looking at tidal effects or standing in a remote frame of reference you can distinguish them.

But, but,but, sputter, sputter...

Captain Kirk was on a Hollywood set, but really, except for the real-life space station, just about every scifi book ever written includes "induced gravity" so the crew could move around "normally," right? Even "2001" had the station turning, didn't it?

Back to the Future!!!

[Adelie]

Originally Posted by TeddyDiver

Can you prove that? All objects with a mass have gravitational pull between each other. For the sake of "simplicity" lets assume the craft is a sphere and the hull has constant thickness and density.

Ps. A looong time ago when I was in highschool this question popped in to my mind in the middle of booooring lesson. Anyway had something to do next week solving it..

For the specific situation you described there would be no net gravitational attraction between you and the space craft wherever you are within the sphere. Attraction to opposing sides cancels out.

There is a discussion and maybe a proof in the 2nd quarter of the Halliday&Resnick college physics book for charged spheres and the net electrical field within. Since the attraction force equations are the same the effect is the same for gravitational fields and effects.

I once used this to calculate the potential energy between the surface and center of the earth falling in a tube under vacuum conditions.


Sent from my iPhone using Cruisers Sailing Forum

[LakeSuperior]

Sorry I wrote this out and then lost it but Einstein recognizing that there was no way to tell the difference between acceleration and gravity was a giant leap in the formulation of The Theory of General Relativity.





"
(Click for a larger version)
The principle of equivalence says that gravity is not a force at all, but is in fact the same thing as acceleration
(Source: Time Travel Research Center: http://www.zamandayolculuk.com/cetinbal/
HTMLdosya1/RelativityFile.htm)
Einstein’s ground-breaking realization (which he called “the happiest thought of my life”) was that gravity is in reality not a force at all, but is indistinguishable from, and in fact the same thing as, acceleration, an idea he called the “principle of equivalence”. He realized that if he were to fall freely in a gravitational field (such as a skydiver before opening his parachute, or a person in an elevator when its cable breaks), he would be unable to feel his own weight, a rather remarkable insight in 1907, many years before the idea of freefall of astronauts in space became commonplace.
A simple thought experiment serves to clarify this: if an astronaut in the cabin of a spacecraft accelerating upwards at 9.8 metres per second per second (the same acceleration as gravity imparts to falling bodies near the Earth’s surface) were to drop a feather and hammer they too would hit the floor of the cabin simultaneously (in the absence of air resistance), exactly as would have happened if they had fallen on Earth under gravity. That, and the feeling of his feet being glued to the ground just as they would be in Earth’s gravity, would be enough to convince the astronaut that the acceleration of the spaceship was indistinguishable from the pull of gravity on the Earth. "


Gravity and Acceleration - Special and General Relativity - The Physics of the Universe