a) Lech is single, and when he walks down the street, he moves with no one forcing him to move. He moves on his own accord.
b) Indentical twins, Dawn and Joy, are in love with Lech. Wherever he goes, Dawn is in front of him, pulling him at the waist. At the same time, Joy is in back of him, pushing him with the same exact force at the waist. Their mental telepathy is such that they always push and pull with the same force.
A few observations:
-Lech moves on his own accord in both scenarios, with the same effort;
-in situation a, we can clearly say that Lech is moving with no external force. In situation b, is it accurate to say that there is no external force, or is it accurate to say that the sum of the external forces is zero?
-situation “b” is the same as the “inside the sphere”
-situation “b” is unstable. If there is the slighest difference in Dawn and Joy’s force, Lech will feel it.
Two more things. Regarding the Nasa statement- notice that they say “The gravitational force everywhere inside the sphere is EQUAL to zero”. They are stating that the sum of the forces equals to zero. That is a different statement than what you stated above “The gravitational force inside a sphere is zero”.
That may seem like splitting hairs, but it is not, per my explanation above. Secondly, the”zero gravity” inside a sphere is what is called “unstable”, meaning that the slighest pertubation in the sphere’s geometry will render this situation into oblivion. In fact, there would be a net gravitational pull.
I couldn’t find the blurb on the Nasa site, but I googled it, and farnkly speaking, folks are getting alot of concepts confused. Let’s go through some concepts one-by-one:
-what we call “gravity” is actually a subset of of a broader physical concept: the attraction of masses. Any two masses will exert an attractive force on each other, in proportion to their mass. In the case of our relationship to the earth, since it’s mass is so much larger to us, we call this effect :gravity”, in which it appears that we are falling down to earth. But actually, both bodies move to each other, yet the earth’s movement towards you is infinitesimally small.
-the term “weightlessness” has no meaning in physics. It is a term that is used in popular culture to describe various phenomena where it appears that gravity has been voided. For instance, on the moon, the gravitational force is actually less due to its smaller mass. On supersonic planes doing certain maneuvers, it can also appear that you are “weightless”. These two phenomena are DIFFERENT, and that is why the term “weightlessness” has no meaning in physics.
-now, inside the hollow sphere: what is happening is that the gravitational forces from each element along the sphere’s circumference add up such that one appears to be “weightless”. However, please note the following:
a) there are gravitational forces. This is NOT a “zero gravity” situation. The way one can think of it is that the gravitational forces are acting like guys wires to keep you suspended (kind of like a puppet).
b) the lay person would call this situation “weightlessness”. As I said above, however, the term “weightlessness” has no meaning in physics. It is a sensation, not a physical phenomenon. For instance, the feeling of “weightlessness” inside a hollow sphere is due to a phenomenon (balance of gravitational forces) that is different than the situation on the moon (REDUCED gravitational forces).
So, to go to your statement above. This statement is incorrect: “At all point within the sphere the gravitational field would be zero.”
The correct statement is “At all points within the sphere the gravitational forces from the sphere would have an effect of making one feel weightless”.
lech- though that means that inside of a uniform sphere is a great place for a date- as the only two bits of mass inside the sphere, you’ll be inescapably attracted to one another.
You’re agreeing with me benson. You’re just taking issue with terminology. The net effect is as I described it.
Correction:
I meant to say that Dawn and Joy are each PULLING in the above scenario.
Two situations:
a) Lech is single, and when he walks down the street, he moves with no one forcing him to move. He moves on his own accord.
b) Indentical twins, Dawn and Joy, are in love with Lech. Wherever he goes, Dawn is in front of him, pulling him at the waist. At the same time, Joy is in back of him, pushing him with the same exact force at the waist. Their mental telepathy is such that they always push and pull with the same force.
A few observations:
-Lech moves on his own accord in both scenarios, with the same effort;
-in situation a, we can clearly say that Lech is moving with no external force. In situation b, is it accurate to say that there is no external force, or is it accurate to say that the sum of the external forces is zero?
-situation “b” is the same as the “inside the sphere”
-situation “b” is unstable. If there is the slighest difference in Dawn and Joy’s force, Lech will feel it.
-Lech is more horny in situation “b”.
anybody seem the other half of that hair?
Lech;
Two more things. Regarding the Nasa statement- notice that they say “The gravitational force everywhere inside the sphere is EQUAL to zero”. They are stating that the sum of the forces equals to zero. That is a different statement than what you stated above “The gravitational force inside a sphere is zero”.
That may seem like splitting hairs, but it is not, per my explanation above. Secondly, the”zero gravity” inside a sphere is what is called “unstable”, meaning that the slighest pertubation in the sphere’s geometry will render this situation into oblivion. In fact, there would be a net gravitational pull.
Lech;
I couldn’t find the blurb on the Nasa site, but I googled it, and farnkly speaking, folks are getting alot of concepts confused. Let’s go through some concepts one-by-one:
-what we call “gravity” is actually a subset of of a broader physical concept: the attraction of masses. Any two masses will exert an attractive force on each other, in proportion to their mass. In the case of our relationship to the earth, since it’s mass is so much larger to us, we call this effect :gravity”, in which it appears that we are falling down to earth. But actually, both bodies move to each other, yet the earth’s movement towards you is infinitesimally small.
-the term “weightlessness” has no meaning in physics. It is a term that is used in popular culture to describe various phenomena where it appears that gravity has been voided. For instance, on the moon, the gravitational force is actually less due to its smaller mass. On supersonic planes doing certain maneuvers, it can also appear that you are “weightless”. These two phenomena are DIFFERENT, and that is why the term “weightlessness” has no meaning in physics.
-now, inside the hollow sphere: what is happening is that the gravitational forces from each element along the sphere’s circumference add up such that one appears to be “weightless”. However, please note the following:
a) there are gravitational forces. This is NOT a “zero gravity” situation. The way one can think of it is that the gravitational forces are acting like guys wires to keep you suspended (kind of like a puppet).
b) the lay person would call this situation “weightlessness”. As I said above, however, the term “weightlessness” has no meaning in physics. It is a sensation, not a physical phenomenon. For instance, the feeling of “weightlessness” inside a hollow sphere is due to a phenomenon (balance of gravitational forces) that is different than the situation on the moon (REDUCED gravitational forces).
So, to go to your statement above. This statement is incorrect: “At all point within the sphere the gravitational field would be zero.”
The correct statement is “At all points within the sphere the gravitational forces from the sphere would have an effect of making one feel weightless”.
lech- though that means that inside of a uniform sphere is a great place for a date- as the only two bits of mass inside the sphere, you’ll be inescapably attracted to one another.
later than you!
ugh… here late for no good reason at all.