Physics Conceptual Question

[BALIstik916]

Hey guys this will score me some extra credit on my final...I appreciate the help in advance

The official question is sorta in 2 parts

1. Where are you exempt from gravitational forces?

2. If gravity is a force then why isn't it in contact with us? (Prof told us that forces must be 2 things in contact)

Appreciate the help


EDIT: Apparently the answer was "graviton"...Just one word, no explanation, if you had the word graviton on your paper you got the extra credit...

 

[Fenixgoon]

Originally posted by: BALIstik916
Hey guys this will score me some extra credit on my final...I appreciate the help in advance

The official question is sorta in 2 parts

1. Where are you exempt from gravitational forces?

2. If gravity is a force then why isn't it in contact with us? (Prof told us that forces must be 2 things in contact)

Appreciate the help

1) when you are in free fall (your acceleration is equal to, and in the same direction, as the gravitational acceleration). when you are at an infinite distance from any mass.
edit: clarification: the net force is 0 during free fall. for a truly 0 gravitational force, either your mass has to be 0, the other object's mass is 0, or you are infinitely apart.

2) gravitational force is not a contact force. it is a mutual attraction between two objects based on their mass and the square of their distance, Gm1m2/r^2

physics majors feel free to correct me

 

[Gibsons]

For the first one, I'm just reminded of a Feynman story... someone asked him if antigravity devices were possible, he said something like that chair you're in works pretty well. That's probably not the answer though!

For the second one, I don't get it, magnets don't have to be in contact to exert a force, do they?

 

[LostUte]

Originally posted by: BALIstik916
Hey guys this will score me some extra credit on my final...I appreciate the help in advance

The official question is sorta in 2 parts

1. Where are you exempt from gravitational forces?

2. If gravity is a force then why isn't it in contact with us? (Prof told us that forces must be 2 things in contact)

Appreciate the help

In the same way that magnets and electrical charges need to be in contact?

 

[her209]

Originally posted by: BALIstik916
1. Where are you exempt from gravitational forces?

Soviet Russia

2. If gravity is a force then why isn't it in contact with us? (Prof told us that forces must be 2 things in contact)

Gravity is not a force.

F=m*a

 

[RedArmy]

For the first question, gravity exists everywhere (so I guess it's a trick question)

For the second one...what her209 said.

 

[troytime]

if you have no mass, you have no gravitational pull

 

[Goosemaster]

Originally posted by: her209

Originally posted by: BALIstik916
1. Where are you exempt from gravitational forces?

Soviet Russia

2. If gravity is a force then why isn't it in contact with us? (Prof told us that forces must be 2 things in contact)

Gravity is not a force.

F=m*a

Would it be wrong to describe gravity as a state relative to the population density of neighboring matter?

 

[Eeezee]

Consider a universe with only one planet (ignoring stars, galaxies, etc., you're just worried about the Earth).

If you are at the center of the Earth, then your gravitational potential is effectively zero. In other words, the Earth is around you in every direction, and the sum of the forces equal zero. This isn't quite what the question asked though; you are still being effected by gravity, you're just being effected in every direction equally (so the net sum is zero). You really can't go anywhere and be exempt from gravity. The professor knows that 75% of the class will write "rofl there is no gravity in outer space!" You're smarter than that and realize that gravity is everywhere.

If gravity worked more like electromagnetism you could just burrow a little inside the earth. The electric field inside a conductor is zero. Unfortunately there really is no such thing as a "gravitational conductor."

As for the second part, I don't have a good explanation. Her209, why do you claim that gravity is not a force? F= - GMm/r^2, yes? Gravity is one of the four fundamental forces. They all act at a distance. In the standard model, the act via forces carriers (electromagnetism - photons, weak - W and Z bosons, strong - gluons, gravity - uknown particle, theoretical graviton, possibly the Higgs boson). That's what makes the four fundamental forces so fun. Friction is just electromagnetism in action. Van der Waals forces = Dipole forces = electromagnetism.

Maybe I'm confused on why force has to be defined in such a way.

 

[BALIstik916]

Eeezee is correct...gravity is one of the four fundamental forces. Your answer to #1 sounds right and no one in my class is stupid enough to write outer space because he distinctly said that is not the answer.

#2 is kind of difficult and I don't know if I am phrasing it correctly. Why is gravity considered a force if it is not in direct contact with us. And to magnets and charges...don't electrical fields dictate contact?

 

[LostUte]

Originally posted by: BALIstik916
Eeezee is correct...gravity is one of the four fundamental forces. Your answer to #1 sounds right and no one in my class is stupid enough to write outer space because he distinctly said that is not the answer.

#2 is kind of difficult and I don't know if I am phrasing it correctly. Why is gravity considered a force if it is not in direct contact with us. And to magnets and charges...don't electrical fields dictate contact?

Assuming that is true, why doesn't the gravitational field "dictate contact?"

 

[Jeff7]

Burrow down into subspace somehow, or find the Timeship from ST: Voyager, which was trying to "push Voyager out of the spacetime continuum" at one point. Get out of spacetime, and you'll be exempt from gravity, as well as most of our reality.

 

[her209]

Originally posted by: Eeezee
Her209, why do you claim that gravity is not a force? F= - GMm/r^2, yes?

The formula you gave is to calculate gravitational force between two masses. Gravity is a constant.

 

[Lorax]

1. reduce mass or go to the center of the earth/surround yourself with equal mass on all sides (?), although the comment about terminal velocity is also correct i think.

2. no clue

 

[LordSnailz]

tagged

 

[PowerEngineer]

I suspect that both questions are bound to have somewhat "tricky" answers.

If the intent of the first question is more along the lines of: "when you will be unaware or not able to sense gravity" (i.e. weightless), then I think that Fexigoon had the right idea. It's the resistance to the pull of gravity that creates the feeling of weight; giving into it completely makes you weightless.

The second question may be fishing for Einstein's characterization of gravity as a warping of the space-time continuum by the two masses involved rather than a force directly between the two masses.

And you need to split the extra credit with us...

 

[DangerAardvark]

Isn't gravity just a "bend" in space/time? In that sense, it makes "contact" through the "bends".

 

[Jeff7]

Originally posted by: DangerAardvark
Isn't gravity just a "bend" in space/time? In that sense, it makes "contact" through the "bends".

As I understand it, if you're traveling in a straight line through space, and you hit the spacetime curvature generated by mass, you're still traveling in a straight line, but through a curved medium. I think that's how it works, anyway.

 

[BALIstik916]

Originally posted by: PowerEngineer

And you need to split the extra credit with us...

lol i will most definitely cite my source but my teacher is one of those professors that thinks he's never wrong and will disagree with "gravitational fields" although I believe they dictate contact

 

[DangerAardvark]

Originally posted by: Jeff7

Originally posted by: DangerAardvark
Isn't gravity just a "bend" in space/time? In that sense, it makes "contact" through the "bends".

As I understand it, if you're traveling in a straight line through space, and you hit the spacetime curvature generated by mass, you're still traveling in a straight line, but through a curved medium. I think that's how it works, anyway.

You know I've always wondered, since the space/time medium encompasses 4 "dimensions", what fuckin' dimension does it bend in? I only took Physics 150 in college so the prof just goes: "space/time bends" and we just mutely write it down in our notebooks. I never had the wherewithal to raise my hand and go "umm... what?"

 

[Googer]

Antigravity.

 

[Jeff7]

Originally posted by: DangerAardvark
You know I've always wondered, since the space/time medium encompasses 4 "dimensions", what fuckin' dimension does it bend in? I only took Physics 150 in college so the prof just goes: "space/time bends" and we just mutely write it down in our notebooks. I never had the wherewithal to raise my hand and go "umm... what?"

Imagine what a 4-dimensional cube looks like. That'll probably help. Good luck.

The closest you'll probably get is a tesseract, which Carl Sagan described as a "shadow" of a 4-dimensional cube, just as a square is a "shadow" of a 3-dimensional cube.
If you only existed in two dimensions, and new of a square. Could you conceive of the direction in which that "extra" dimension existed?

The analogy you may have seen before is the "rubber sheet," wherein space is reduced to two dimensions, leaving time as the third - objects with mass curve the sheet downward. Something passing by will "fall" toward the object with mass. If it lacks sufficient velocity, it will become trapped by the gravity well, and either enter orbit, or collide.

Orbiting, as I understand it: You're falling toward the planet, but you're also moving forward. As you move forward, the ground, by nature of the spherical shape of the planet, is moving away from you. In that reference frame, you're in free-fall, falling toward a surface which is constantly curving away from you, yet because of your constant falling, you are able to remain equidistant from it.
Addition: Inertia also helps to keep you moving in a "straight" line, relative to the surface of the object you're orbiting.

 

[pray4mojo]

gravity is not a force. but theres a force due to gravity called weight.

 

[DangerAardvark]

Originally posted by: Jeff7

Originally posted by: DangerAardvark
You know I've always wondered, since the space/time medium encompasses 4 "dimensions", what fuckin' dimension does it bend in? I only took Physics 150 in college so the prof just goes: "space/time bends" and we just mutely write it down in our notebooks. I never had the wherewithal to raise my hand and go "umm... what?"

Imagine what a 4-dimensional cube looks like. That'll probably help. Good luck.

The closest you'll probably get is a tesseract, which Carl Sagan described as a "shadow" of a 4-dimensional cube, just as a square is a "shadow" of a 3-dimensional cube.
If you only existed in two dimensions, and new of a square. Could you conceive of the direction in which that "extra" dimension existed?

The analogy you may have seen before is the "rubber sheet," wherein space is reduced to two dimensions, leaving time as the third - objects with mass curve the sheet downward. Something passing by will "fall" toward the object with mass. If it lacks sufficient velocity, it will become trapped by the gravity well, and either enter orbit, or collide.

Orbiting, as I understand it: You're falling toward the planet, but you're also moving forward. As you move forward, the ground, by nature of the spherical shape of the planet, is moving away from you. In that reference frame, you're in free-fall, falling toward a surface which is constantly curving away from you, yet because of your constant falling, you are able to remain equidistant from it.

I'm imagining the shit out of that cube. You don't even know...

But maybe I was confused, but I thought the "rubber sheet" was space along one axis and time along the other, with mass distorting it in some mystery dimension. But what you're saying is the sheet is space and mass distorts space in the "direction" of time?

 

[Random Variable]

Originally posted by: her209

Originally posted by: BALIstik916
1. Where are you exempt from gravitational forces?

Soviet Russia

2. If gravity is a force then why isn't it in contact with us? (Prof told us that forces must be 2 things in contact)

Gravity is not a force.

F=m*a

F=ma=GmM/r^2

Contact forces are only one type of force.