Astronomy / Space Question on gravity and acceleration

[Enride]

Being a complete amateur on physics and astronomy I often find myself overthinking subjects, probably due to struggling to understand them at all, to the point of nothing making sense! :S

So lately, ive watched and read alot about gravity and acceleration, a topic I find among the most interesting within physics. But ive stumbled upon a few ideas that is crippling my mind.

If gravity and acceleration is not just similar but actually the same thing (if I understand correctly concluded by the elevator/laboratory thought experiments), how come when gravity accelerates downward I am accelerated downward, but if a spaceship in deep space accelerates downward im accelerated upwards?

Seems to me that when speaking of gravitational acceleration, that acceleration should be said to accelerate AWAY from the mass creating it to have anything influenced by this gravity to accelerate TOWARDS the mass.

Someone explain what Im not grasping?

But as I said, my head is doing its best to wreck me right now

 

[Winterwalker]

Hehe .. Commander Enride ..
The effect you describe are two different scenarios

Elevator thought experiment, you AND the spaceship are both falling at the same speed (acceleration) as BOTH are under the infuence of (the same) gravity.

In the ship example it is the engines causing the acceleration - unless you also have engines, your body doesn't accelerate. The upward effect you mention is your body's equal and opposite reaction (Newton) to the acceleration of the seat/ ship pushing on you.

Gravity and Acceleration aren't exactly the same thing. Gravity is a force that yes, causes you to accelerate, but so does any external force (eg. in a car or a push)

If you like that you'll love ....

[video=youtube;5C5_dOEyAfk]https://www.youtube.com/watch?v=5C5_dOEyAfk[/video]

 

[Enride]

Hehe .. Commander Enride ..
The effect you describe are two different scenarios

Elevator thought experiment, you AND the spaceship are both falling at the same speed (acceleration) as BOTH are under the infuence of same gravity.

In the ship example it is the engines causing the acceleration - unless you also have engines, you won't accelerate at the same speed. (The upward effect you mention is your body's equal and opposite reaction (Newton) to the acceleration of the seat/ ship pushing on you)

Gravity and Acceleration aren't exactly the same thing. Gravity is a force that yes, causes you to accelerate, but so does any external force (eg. in a car or a push)

If you like that you'll love ....

https://www.youtube.com/watch?v=5C5_dOEyAfk

Told you my head is messing with me
My head still hurts though but I think im sorting out where I went wrong, and may soon start to wonder how I could be that dumb!!

The price ill pay for trying to educate myself on the matter!

 

[Winterwalker]

No worries Commander .. it's actually NOT OBVIOUS when you look at gravity / bodies accelerating, because there's another phenomenon in play "inertia".

This depends on how much you weigh, and relates to how difficult it is to accelerate you in any new direction. This is why, if the ship accelerates backwards (and no seatbelt) your body is actually quite determined to stay in the same place. Not only will you hit your head on the windscreen but you will do so with a heavier force, the heavier you are (under inertia). Your nose FAILS to react to the windshield .. crunch. Only your head is strong enough to find, the equal and opposite Reaction Force, which is enough to bring your body up to equal speed with the ship.

---

VERY addtional; The NASA experiment is a little bit of a con trick. Gallileo was a great scientist but an earlier one, who came before Newton. Newton later discovered that the force on the feather and hammer, although so close it makes no difference for the video, receive different acceleration forces from the moon's gravity. The gravitation attraction (causing the acceleration) between any two objects depends on the distance between, and on the mass of BOTH objects (Law). Of course the moon is very much bigger than both feather and hammer so, for the sake of a video you probably can't spot it, the hammer will only hit a tiny bit first because both are relatively very much smaller than the moon.

Worser though .. if you were floating above the moon (being aware of "internal" versus "external" forces) and if you magically produced a feather out of nowhere, the moon would be attracted to the feather. If the feather couldn't move and if the moon is affected by no other forces, the moon will begin to accelerate towards the feather, faster and faster (as the gravity force increases the closer you get) and they WILL eventually touch. Under (a very small) acceleration, the moon will begin to approach the feather, extra slowly because the Moon suffers from having high inertia. But BECAUSE it has a high inertia, once the moon starts to move, it will be very difficult to stop.


(I think I'll have a little sit down now )

 

[Surfinjo]

A poser was put to me and some others as a thought problem, a number of years ago.

The universe is emptied of all matter leaving only the vastness of space.

Two particles of equal mass are placed at opposite end of the universe.

What happens?

Repeat, but with one particle, twice the mass of the second.

The results are quite interesting.

 

[Zieman]

Doesn't that thought experiment fail at the "opposite ends of the universe" part?

 

[Surfinjo]

Doesn't that thought experiment fail at the "opposite ends of the universe" part?

Nope...................

 

[Zieman]

Interesting. What are the opposite ends then? Start and end of time?

 

[Zieman]

Oh come on, please tell us how the thought experiment went - can't figure it out myself...

I can only borrow an idea from Alastair Reynolds (don't know where he got it, was in one of his books): big bang for all 3 particles.

 

[bitstorm]

if a spaceship in deep space accelerates downward im accelerated upwards?

Simply put, you're not. You stay in the same place but you can't because there's a seat in the way.

 

[Enride]

No worries Commander .. it's actually NOT OBVIOUS when you look at gravity / bodies accelerating, because there's another phenomenon in play "inertia".

This depends on how much you weigh, and relates to how difficult it is to accelerate you in any new direction. This is why, if the ship accelerates backwards (and no seatbelt) your body is actually quite determined to stay in the same place. Not only will you hit your head on the windscreen but you will do so with a heavier force, the heavier you are (under inertia). Your nose FAILS to react to the windshield .. crunch. Only your head is strong enough to find, the equal and opposite Reaction Force, which is enough to bring your body up to equal speed with the ship.

---

VERY addtional; The NASA experiment is a little bit of a con trick. Gallileo was a great scientist but an earlier one, who came before Newton. Newton later discovered that the force on the feather and hammer, although so close it makes no difference for the video, receive different acceleration forces from the moon's gravity. The gravitation attraction (causing the acceleration) between any two objects depends on the distance between, and on the mass of BOTH objects (Law). Of course the moon is very much bigger than both feather and hammer so, for the sake of a video you probably can't spot it, the hammer will only hit a tiny bit first because both are relatively very much smaller than the moon.

Worser though .. if you were floating above the moon (being aware of "internal" versus "external" forces) and if you magically produced a feather out of nowhere, the moon would be attracted to the feather. If the feather couldn't move and if the moon is affected by no other forces, the moon will begin to accelerate towards the feather, faster and faster (as the gravity force increases the closer you get) and they WILL eventually touch. Under (a very small) acceleration, the moon will begin to approach the feather, extra slowly because the Moon suffers from having high inertia. But BECAUSE it has a high inertia, once the moon starts to move, it will be very difficult to stop.


(I think I'll have a little sit down now )

Ill sit down beside ya mate! Thanks for the time taken to reply though, I really appreciate it!

A poser was put to me and some others as a thought problem, a number of years ago.

The universe is emptied of all matter leaving only the vastness of space.

Two particles of equal mass are placed at opposite end of the universe.

What happens?

Repeat, but with one particle, twice the mass of the second.

The results are quite interesting.

I guess, since gravitational effect on spacetime is supposedly endless, that the particles would begins to "fall" towards eachother.
In the case of the asymetrical particles, they eventually meet closer to the beginning of the bigger particle.

Since this is probably not true, i hope you will fill us in on what your answer/conclusion is

Simply put, you're not. You stay in the same place but you can't because there's a seat in the way.

Good and simple explanation which is easy to understand.
Im getting grip on the situation, I was too much focusing on the acceleration and its effect being the same no matter WHAT is causing the acceleration.

 

[Surfinjo]

I guess, since gravitational effect on spacetime is supposedly endless, that the particles would begins to "fall" towards eachother.
In the case of the asymetrical particles, they eventually meet closer to the beginning of the bigger particle.

Since this is probably not true, i hope you will fill us in on what your answer/conclusion is

Not really sure why you felt it was some sort of riddle. Though you may have missed the contribution of acceleration.

It wasn't intended to catch anyone out. Just something that I recall after reading the OP. It amused me at the time. Decided to share it.

Chill people.

 

[Zieman]

Not really sure why you felt it was some sort of riddle. Though you may have missed the contribution of acceleration.

It wasn't intended to catch anyone out. Just something that I recall after reading the OP. It amused me at the time. Decided to share it.

Chill people.

Can't chill, the tinfoil hat reflects the heat from my head back to my head.

But as there was no trickery in the thought experimet, Enride's anwers looks good. Identical particles collide at the center of the otherwise empty universe, asymmetric pair collides at ~33% of the original distance from heavier particle's start position?

 

[Space Fan]

Being a complete amateur on physics and astronomy I often find myself overthinking subjects, probably due to struggling to understand them at all, to the point of nothing making sense! :S

So lately, ive watched and read alot about gravity and acceleration, a topic I find among the most interesting within physics. But ive stumbled upon a few ideas that is crippling my mind.

If gravity and acceleration is not just similar but actually the same thing (if I understand correctly concluded by the elevator/laboratory thought experiments), how come when gravity accelerates downward I am accelerated downward, but if a spaceship in deep space accelerates downward im accelerated upwards?

Seems to me that when speaking of gravitational acceleration, that acceleration should be said to accelerate AWAY from the mass creating it to have anything influenced by this gravity to accelerate TOWARDS the mass.

Someone explain what Im not grasping?

But as I said, my head is doing its best to wreck me right now

Yep, genuine Master of Astrophysics here. It's a great question, and you're in the same company as Einstein. You can't distinguish between gravity and acceleration.

 

[Enride]

Not really sure why you felt it was some sort of riddle. Though you may have missed the contribution of acceleration.

It wasn't intended to catch anyone out. Just something that I recall after reading the OP. It amused me at the time. Decided to share it.

Chill people.

Sorry if I somehow offended you, it was not at all my intention and I did in no way take any offense by your post either.
You just put it out there in a way that made me think it was a trick question!
And I have no problem with trick questions, its a great way to learn new stuff

 

[Space Fan]

See my post above. Sigh.

 

[Enride]

See my post above. Sigh.

What you sighing about, mate? I did see your post and dont recall questioning any of it?
I was only responding to surf how i misinterprited his earlier post.

 

[Winterwalker]

Yep, genuine Master of Astrophysics here. It's a great question, and you're in the same company as Einstein. You can't distinguish between gravity and acceleration.

"I love the smell of the universe in the morning."
— Neil deGrasse Tyson


.. and looking at these Stars "suddenly dwarfed my own troubles and all the gravities of terrestrial life. I thought of their unfathomable distance and the slow inevitable drift of their movements, out of the unknown past into an unknown future." — Herbert George Wells

 

[Surfinjo]

Yep, genuine Master of Astrophysics here. It's a great question, and you're in the same company as Einstein. You can't distinguish between gravity and acceleration.

Wot wood there be?