# Is it possible that the gravity that keeps our feet planted on the Earth is..

The sun's gravity would be pulling equally on the Earth beneath me. We would fall at the same speed towards the Sun according to Newton's law.

Then why do you say that the earth needs to be pushing you?

Then why do you say that the earth needs to be pushing you?

Now I understand why you asked your question. Look, this is no longer a debate as to whether or not there is gravity. However, I still want to examine the possible significance of the way the Earth moves has in contributing to keeping things on its surface and keeping gravity more or less equal on its surface. Everyone here says that it has no bearing on gravity whatsoever, but I say that it is too coincidental that the Earth and other planets move the way they do to ignore. Even if the the movements would not be enough to cause the amount of acceleration that we measure from gravity, they still would help keep the planets' round shape and therefore keep things on their surfaces.

This is why I want to explore where projectiles from the surface of the Earth would go if there were no gravity.

Now I understand why you asked your question. Look, this is no longer a debate as to whether or not there is gravity. However, I still want to examine the possible significance of the way the Earth moves has in contributing to keeping things on its surface and keeping gravity more or less equal on its surface. Everyone here says that it has no bearing on gravity whatsoever, but I say that it is too coincidental that the Earth and other planets move the way they do to ignore. Even if the the movements would not be enough to cause the amount of acceleration that we measure from gravity, they still would help keep the planets' round shape and therefore keep things on their surfaces.

This is why I want to explore where projectiles from the surface of the Earth would go if there were no gravity.
What is this coincidence?

Where projectiles from the surface of the Earth would go if there were no gravity? Well, if we switched off universal gravity, the projectiles would just fly off into deep space, provided there's no atmospheric resistance.

Einstein's most notable thought experiment lead to his equivalence principle, where he compared the force caused by Newton's gravitation to an inertial force. Are you trying to go beyond this and, if so, please explain.

Well, I think that gravity basically funnels momentum that an object already has into one direction towards the center of the planet.

I think this because of the calculation I did where the acceleration from 0 to the magnitude of the resultant vector of the Earths major movements relative to the center of the galaxy (~212km/s) over exactly 1/4 of the time it takes for the Earth to complete 1 full rotation (~359 minutes. I don't have the more precise number on my phone right now) equals 9.81m/s^2. Also, the planets with the most mass and gravity rotate the fastest. I don't think that is coincidental.

If space-time is curved, it would make sense that mass attraction would be unnecessary to create acceleration towards the planet. It would simply funnel inertial momentum into a vector towards the planet without any proper acceleration.

(The following explanation is especially difficult for me to find the right words to convey my thoughts with the proper physics vernacular. Please do your best to decipher what I am trying to say)

Because the center of the planet changes position relative to an object passing the planet less often the further away the object is from the center of the planet, gravity would seem to be weaker at greater distances. If an object can equalize its momentum in a direction perpendicular to the center of the planet, its own inertia will allow it to resist the change in direction enough to prevent it from pointing straight towards the planet and prevent it from colliding with it, creating an orbit.

What is this coincidence?

Where projectiles from the surface of the Earth would go if there were no gravity? Well, if we switched off universal gravity, the projectiles would just fly off into deep space, provided there's no atmospheric resistance.

What do you not understand about trying to isolate a component?

I just want to add something that doesn't make sense to me with my current knowledge that might make sense to you guys. If so, could you please explain it to me?

From what I gather according to Newton's law of universal gravitation, gravity is supposed to be stronger the closer we get to large amounts of mass.

If this is true, then wouldn't gravity towards the center of the planet be weaker the closer we get to it if we were in a tunnel going straight down? The deeper we go, the more and more mass there would be on our opposite side. If there were no atmosphere to press down on us, the effect would be especially weaker. If we were to tunnel down to about 5000km while filling in the hole as we dug and creating a cylindrical cavity, and then drop something, wouldn't it fall with less acceleration instead of more?

Well, I think that gravity basically funnels momentum that an object already has into one direction towards the center of the planet.

I think this because of the calculation I did where the acceleration from 0 to the magnitude of the resultant vector of the Earths major movements relative to the center of the galaxy (~212km/s) over exactly 1/4 of the time it takes for the Earth to complete 1 full rotation (~359 minutes. I don't have the more precise number on my phone right now) equals 9.81m/s^2. Also, the planets with the most mass and gravity rotate the fastest. I don't think that is coincidental.

If space-time is curved, it would make sense that mass attraction would be unnecessary to create acceleration towards the planet. It would simply funnel inertial momentum into a vector towards the planet without any proper acceleration.

(The following explanation is especially difficult for me to find the right words to convey my thoughts with the proper physics vernacular. Please do your best to decipher what I am trying to say)

Because the center of the planet changes position relative to an object passing the planet less often the further away the object is from the center of the planet, gravity would seem to be weaker at greater distances. If an object can equalize its momentum in a direction perpendicular to the center of the planet, its own inertia will allow it to resist the change in direction enough to prevent it from pointing straight towards the planet and prevent it from colliding with it, creating an orbit.

Two problems with this idea. First, "funnel[ing] inertial momentum into a vector towards the planet without any proper acceleration" is a contradiction in terms. A changing velocity vector is the definition of acceleration (and as long as mass stays constant, changing velocity is equivalent to changing momentum). Second, if gravity only redirects existing momentum, gravity would exert no pull between two bodies that were stationary relative to each other. If you stand on one of the poles, you're not rotating around the Earth at all, but gravity still holds you down. In fact, that's a general objection to any hypothesis that gives the Earth's rotation a significant role in keeping objects on the surface: if any such hypothesis were true, a person's effective weight would be noticeably different between the equator and the poles. It's not.

Edited footnote: That calculation you did, with the speed of the Earth around the galaxy and whatnot? That sort of number crunching is sometimes referred to as "numerology" in scientific circles, and it's something you should avoid. The basic idea is that the more numbers you're looking at, the more likely you are to find a coincidence between them, which will lead you to think there's a connection when in fact there is none. The correct approach is to first figure out the exact math of your hypothesis, then see if the real world matches it.

I just want to add something that doesn't make sense to me with my current knowledge that might make sense to you guys. If so, could you please explain it to me?

From what I gather according to Newton's law of universal gravitation, gravity is supposed to be stronger the closer we get to large amounts of mass.

If this is true, then wouldn't gravity towards the center of the planet be weaker the closer we get to it if we were in a tunnel going straight down? The deeper we go, the more and more mass there would be on our opposite side. If there were no atmosphere to press down on us, the effect would be especially weaker. If we were to tunnel down to about 5000km while filling in the hole as we dug and creating a cylindrical cavity, and then drop something, wouldn't it fall with less acceleration instead of more?

Yep! If you think about it, it makes sense - as you pass through the Earth's core, gravity switches directions. In order for that transition to happen smoothly, the strength of gravity has to decrease to zero as you descend to the core, then increase again as you ascend on the other side.

Two problems with this idea. First, "funnel[ing] inertial momentum into a vector towards the planet without any proper acceleration" is a contradiction in terms. A changing velocity vector is the definition of acceleration (and as long as mass stays constant, changing velocity is equivalent to changing momentum). Second, if gravity only redirects existing momentum, gravity would exert no pull between two bodies that were stationary relative to each other. If you stand on one of the poles, you're not rotating around the Earth at all, but gravity still holds you down. In fact, that's a general objection to any hypothesis that gives the Earth's rotation a significant role in keeping objects on the surface: if any such hypothesis were true, a person's effective weight would be noticeably different between the equator and the poles. It's not.

Edited footnote: That calculation you did, with the speed of the Earth around the galaxy and whatnot? That sort of number crunching is sometimes referred to as "numerology" in scientific circles, and it's something you should avoid. The basic idea is that the more numbers you're looking at, the more likely you are to find a coincidence between them, which will lead you to think there's a connection when in fact there is none. The correct approach is to first figure out the exact math of your hypothesis, then see if the real world matches it.

Yep! If you think about it, it makes sense - as you pass through the Earth's core, gravity switches directions. In order for that transition to happen smoothly, the strength of gravity has to decrease to zero as you descend to the core, then increase again as you ascend on the other side.

As you get closer to the poles you are not rotating as much, but you are moving up and down more relative to the center of the Earth on the plane of its orbit around the Sun. If you were standing on the exact axial pole, your body would be essentially wobbling relative to that same plane. I wonder if something thrown straight up from that point would actually fall straight back down. I think it would land off to the side somewhere.

Sorry I didn't reply to all of your points. I'm on my phone and it is difficult to quote different parts of a post with it.

You could say that every body is stationary relative to one other body or no bodies are stationary relative one other body.

What body is completely still? The particles that make up an object certainly aren't still. Two objects separated by space on the surface of the Earth aren't still. Think of the Coriolis effect on the surface of the Earth. Think of circular motion, where an object on the Earth closer to the sun is moving slower than an object further away from it.

I don't see how we could even test this idea because we can't guarantee 2 objects aren't moving relative to each other.

If gravity doesn't funnel momentum, where does it get the energy from to accelerate an object?

What I meant by funneling is that it doesn't add any energy to an object. It just focuses it.

NHowever, I still want to examine the possible significance of the way the Earth moves has in contributing to keeping things on its surface and keeping gravity more or less equal on its surface.

That is a valid question; however, most of those forces act to throw things off the surface. (After all that's what tides are.)

Well, I think that gravity basically funnels momentum....

...
Because the center of the planet changes position relative to an object passing the planet less often the further away the object is from the center of the planet, gravity would seem to be weaker at greater distances. If an object can equalize its momentum in a direction perpendicular to the center of the planet, its own inertia will allow it to resist the change in direction enough to prevent it from pointing straight towards the planet and prevent it from colliding with it, creating an orbit.

I would like to get some clarity on what you are trying to say here in your last paragraph quoted above. I don't understand your first sentence of the last paragraph. In the second sentence, again I don't understand what you are trying to communicate. As well, you can't have something perpendicular to the centre of the planet. It can either be radial (passing through the centre) or tangential.

That being said I will offer the following. The spin of the earth reduces the force pulling you down. If the earth stopped spinning and you had an accurate weigh scale, you would weigh slightly more. If you could vary the speed of the earth's rotation, as it speeds up you would get to a point where the speed of rotation would create a centrifugal force that would be equal to the force of gravity and, as long as the rotational acceleration to get from the current speed to that critical speed was gradual enough, the only sensation you would detect is becoming weightless.

I would like to get some clarity on what you are trying to say here in your last paragraph quoted above. I don't understand your first sentence of the last paragraph. In the second sentence, again I don't understand what you are trying to communicate. As well, you can't have something perpendicular to the centre of the planet. It can either be radial (passing through the centre) or tangential.

That being said I will offer the following. The spin of the earth reduces the force pulling you down. If the earth stopped spinning and you had an accurate weigh scale, you would weigh slightly more. If you could vary the speed of the earth's rotation, as it speeds up you would get to a point where the speed of rotation would create a centrifugal force that would be equal to the force of gravity and, as long as the rotational acceleration to get from the current speed to that critical speed was gradual enough, the only sensation you would detect is becoming weightless.

I think you're right about most of what you said, but if space is curved and the rotation speed is faster, then you would hit the ground with more force if there was ground there to hit. It's like a perfect combination of rotation speed and surface area.
Then mass comes into play because even if you hit hard, if there isn't enough mass, and therefore inertia, to stop you, you would just plow through whatever you hit or knock it out of your way.

That is a valid question; however, most of those forces act to throw things off the surface. (After all that's what tides are.)

Right, but then there is curved space time to make it come back to the surface.

Edit: one other thing of note is that if you throw something off the Earth the direction of its path around the Sun or Galaxy, it is accelerating in that direction while what you have thrown is not.

I think you're right about most of what you said, but if space is curved and the rotation speed is faster, then you would hit the ground with more force if there was ground there to hit. It's like a perfect combination of rotation speed and surface area.
Then mass comes into play because even if you hit hard, if there isn't enough mass, and therefore inertia, to stop you, you would just plow through whatever you hit or knock it out of your way.

Can you try and explain this in different words or more explicit sentences. I am not following you.

Can you try and explain this in different words or more explicit sentences. I am not following you.

Think of if the Earth rotated 12km/s on its axis. Things would fly off of it and go into an orbit around the Earth. But what if the Earth was bigger than the circumference that that orbit would have? Things would collide with the surface again. What if the Earth was WAY bigger than that orbit would be? Things would never actually fly off the surface, but they would be pushed into it harder.

Think of if the Earth rotated 12km/s on its axis. Things would fly off of it and go into an orbit around the Earth. But what if the Earth was bigger than the circumference that that orbit would have? Things would collide with the surface again. What if the Earth was WAY bigger than that orbit would be? Things would never actually fly off the surface, but they would be pushed into it harder.

How fast does the ISS move? I think it's about 7km/s. It is in low Earth orbit. What if the Earth was less dense, but had the same mass and was bigger than the orbit of the ISS?

How fast does the ISS move? I think it's about 7km/s. It is in low Earth orbit. What if the Earth was less dense, but had the same mass and was bigger than the orbit of the ISS?
it would have to orbit at an even higher altitude.

How fast does the ISS move? I think it's about 7km/s. It is in low Earth orbit. What if the Earth was less dense, but had the same mass and was bigger than the orbit of the ISS?

I assume you want me to assume there is no atmosphere and that the earth is not spinning...

If the earth expanded slowly, when the radii of the earth and ISS's orbit were the same, the stationary earth would come into contact with the moving space station. The ISS would start to drag on the surface of the earth but would have no net force downward, that is until it started slowing down due to the slight amount of friction. If the earth grew no bigger the ISS would continue to slow down and, as it did, its weight or force on the earth's surface would increase, increasing the friction and decreasing its speed even further until it came to rest. If the earth continued to grow, this would simply happen over a shorter period of time.

I assume you want me to assume there is no atmosphere and that the earth is not spinning...

If the earth expanded slowly, when the radii of the earth and ISS's orbit were the same, the stationary earth would come into contact with the moving space station. The ISS would start to drag on the surface of the earth but would have no net force downward, that is until it started slowing down due to the slight amount of friction. If the earth grew no bigger the ISS would continue to slow down and, as it did, its weight or force on the earth's surface would increase, increasing the friction and decreasing its speed even further until it came to rest. If the earth continued to grow, this would simply happen over a shorter period of time.

Not really where I was heading with that.

Think of if the Earth was rotating fast enough to sling you out into the air, but not fast enough for you to escape its gravity. What do you think would happen?