At least you got one thing right, I got to hand you that.
Is it possible that the gravity that keeps our feet planted on the Earth is..
- Thread starter jiveabillion
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jiveabillion
Registered Member
Two things I'd like to check with you:
1) You're aware that you can't just take any idea you want and express it as working math, right? Not every idea can be expressed as an equation, so you can't simply expect to turn it over to a math professor and have them fill in the gaps. Agreed?
2) Why not start with the simplest possible case. Are you aware that the gravitational force between two palm-sized iron balls was already determined 200 years ago by Henry Cavendish? It matches exactly with what Newton determined a century earlier from observing the motions of the planets, but this is something you can measure in your own home with the right equipment. How do you plan on explaining that? How do you plan on explaining the gravitational pull your own body creates?
jiveabillion
Registered Member
My issue with the whole idea is that we would have both this mass attraction and plain old Newtonian mechanics that could make things behave the way they do with gravity. So, which is it? Are they working together? If so, is the gravitational constant not nearly as strong as we think it is?
If momentum must be conserved, why is gravity needed to keep something in orbit? Where does the momentum to travel with the Earth go if gravity is there in its place? Did we not add momentum to the object when we thrust it into space? These are the questions I want answers for.
It's both of course.
Those two questions seem to be related but they aren't. The theories work extremely well, so the gravitational constant must be correct.
Because without gravity, conserved momentum would make an object travel in a straight line instead of in a curve. I seem to remember you mentioning before that there is no acceleration if there is no speed change: that's wrong. Direction change is also acceleration.
That question doesn't make any sense. An object sitting still on earth has zero momentum relative to Earth. I think this is a manifestation of your misunderstanding of relative motion. Regardless, gravity doesn't replace momentum - they are two different things.
Yes. So?
Also, I'm not sure anyone mentioned this before, but your fixation with momentum conservation is odd and inapplicable here*. I'm not sure you are aware, but momentum is not conserved in orbital/projectile motion. Energy is. So it is conservation of energy that is utilized in solving such problems.
*I have a theory that people such as yourself fixate on the last thing they formally learned when they were kids. But I'm not a psychologist.
*I have a theory that people such as yourself fixate on the last thing they formally learned when they were kids. But I'm not a psychologist.
By that standard the gravity map of the moon becomes an inconvenient truth.
You did that when you decided that 9.81 m/s² is derived by finding the orbital plane relative to the center of the galaxy.
My point exactly, which makes your gravity relative to the direction of the center. Every object on Earth would experience weight change depending on the object's orientation to that center. Earth would not orbit the Sun. A lot worse things would be going on.
Gravity is not about relative motion, as you know by the large number of stationary objects affected by gravity.
As you know, gravity will persist when there is no motion.
I think the answers have been quite generous.
It doesn't follow you in your reference frame. Looking out your back window, it's staying behind.
That's not an intelligible question, which probably has something to do with not getting the answer you desire.
Ignoring everything else in this thread (not to minimize the dozens of valid points given)
1. Your idea does not account for Neil Armstrong's weight on the moon, nor the span of his leap.
2. The gravity map of the moon shows changes in field strength at the craters, which would not be possible if you were correct.
jiveabillion
Registered Member
Can't an object's own inertia cause it to change direction without proper acceleration?
jiveabillion
Registered Member
This is why I think inertia and momentum is enough to cause an object to travel in a curve and an orbit. Does anyone here see what I mean?
Basic physics says "no". Crank physics on the other hand....
Sorry, you're getting ahead of me here.
I didn't do well with Dictionay in High School.
No, it can't - that's basically gibberish.
Inertia is the property of matter that resists acceleration, so it can't cause acceleration. And change in direction is acceleration, so you can't have change in direction without acceleration.
Once you have declared the law of gravitation to be false, all of the laws concerning inertia and acceleration fall as well. In your universe, there is no law except the ones you deduce by throwing a ball out of your car.
It would depend on your frame of reference. To an observer that was stationary relative to your moving platform the ball would move forward at 212 km/hr and outward at 100 km/hr making a diagonal path. From the moving platforms reference frame the ball would only move in a straight line away from the platform at 100 km/hr.
This is again a reference frame question. The earth, you, the ball and your uncle Joe are all moving at the same speed through space. The earth is rotating, it is orbiting the sun, our solar system is orbiting the galactic center, the galaxy is hurtling towards the center of the Virgo cluster, etc. When you throw a ball straight up the all the previous speeds stay the same the only thing you have done is added an additional speed in one direction. Gravity causes the ball to accelerate downward at 9.8 m/s^2 the instant it leaves your hand. From your frame of reference (the earth) you will see the speed of the balls slow, stop and then accelerate back to earth.
From a frame of reference that was stationary relative to earth, the sun and the galaxy, you would see the earth go whizzing by and from the time the ball left your hand to when it hit earth again it would trace out a rather interesting path that was a couple hundred kilometers long.
Ah, ok. That explains why you and everyone else seemed to be talking past each other. If pure momentum could keep an object in a circular orbit, I would kind of be able to see where you're coming from. But it can't; you need acceleration to travel on a curved trajectory. That's Newton's first law of motion, and I'm a little surprised that one of our members told you otherwise.
Both Newtonian mechanics and the Newtonian law of gravity are at work here, just the way the equations specify, with the same old gravitational constant. It might be, from what others have posted recently, that you're confused about momentum conservation and take it to be relative to Earth (which wouldn't be correct).
Yeah, I think this is consistent with my suspicions about your notion of momentum conservation. Here's the thing- if the entire lab and everything on it is pulled towards the sun at the same rate (they are at nearly identical distances from the sun), then you can still say that momentum conservation applies to objects in the lab under certain situations, where momentum in this case is measured relative to Earth and the lab. There are situations where the gravitational effect of the sun is not uniform everywhere and the difference is large enough to be noticeable; then you have to take the sun's pull into account (example: the tides arise because of the different gravitational pulls from the moon and sun at different points on Earth located at different distances), and momentum as measured relative to Earth is no longer conserved (total momentum is still conserved, but now you have to include the sun's momentum as well and it can't be measured relative to the accelerating Earth).
If you're doing a tabletop experiment with billiard balls and checking for momentum conservation, then the billiard balls, the table, you and the Earth are all accelerating towards the sun at the same rate, and the acceleration applies equally to every point of your body, and every point of the balls, Earth and table. In this case you won't notice any acceleration from the sun's gravity because it's applying uniformly to everything around your reference point, the entire Earth is effectively in freefall around the sun, and the billiard table will look the same to you as it would if the Earth were simply floating through empty space with nothing to orbit. In this case, and because the Earth's gravity is cancelled out by the table on which the billiard balls are held up, you can argue that in the absence of friction, the total momenta of the billiard balls is conserved regardless of how they collide.
If your argument were right and there were isolated points on Earth (i.e. Antarctica) where things could simply go flying off into space, then what would hold Earth together in the first place? We would expect to see giant columns of snow, gas and dust leaking off into space until there's no Earth left!
jiveabillion
Registered Member
The trajectory of the ball doesn't have to curve. The surface of the Earth will move into it and the surface of the Earth is curved. However, From your frame of reference, the ball's trajectory curves.
It's the center of the Earth that is moving 29.7km/s around the Sun and 225km/s around the galaxy, not its surface. We are not at the center of the Earth, we're about 6,378.10km from it at the equator. Every 6 hours, we travel that distance relative to the center of the Earth at about 0.465km/s or 1674km/hr. While doing this, the surface is pushing "upwards" from the center of the Earth. It can only push against objects that are against something for the surface to push with (the ground, a desk, in your hand, etc). If the surface was pushing a ball with your hand (through your body on the ground) and you move your hand so that it is no longer pushing the ball away from the center, it will "fall". You can pick it back up again and drop it again, because the Earth NEVER stops doing this. While doing this, the Earth is slowing you down and speeding you up proportionately relative to the center of the Earth and it's main directions of travel. I think you can use cos and sin trigonometry functions to calculate the proportions over time.
If you take all of the force vectors and magnitudes being exerted on an object by the Earth and calculate the resultant you can see how it would always put the object on a collision course with the surface of the Earth as it moves. Add in another vector for throwing an object and you will see that, unless you throw it with great magnitude, it will still result in a collision course with the Earth. This is all without gravity. This is why I say we don't need gravity to explain most of what we experience.
I would explain why I think momentum and inertia can create an orbit if carefully worked with, but I doubt that you will be receptive to that if you don't agree with what I've just said above. Regardless, an orbit isn't a circle or an ellipse. Relative to the center of the galaxy, it would be a spiral of sorts. The path that it follows would look different depending on the inclination of the orbit relative to the equator and the prime meridian as well as the eccentricity. Relative to the CMBR, it's anyone's guess what it would look like. I wish I had some software that would simulate this so that I could see it.
The balls flight will only curve if there is a force acting on it, otherwise it will go in a straight line. edit - I think I misunderstood you. The curve you were discussing is that parabolic arc that the ball makes. Your logic is wrong though, thinking that the earth somehow hits the ball instead of gravity causing the arc.
Both the center of the earth and the surface are moving at 29.7km/s around the Sun and 225km/s around the galaxy, it is just that the surface as the addtional speed of rotation.
I don't know what you are trying to say here. It sort of sounds like you are talking about the normal force that results from gravity, but then you talk about the earth speeding you up and slowing you down which does not have any meaning that I can detect.:shrug:
There are no forces from our speed through space. Forces do not develop from speed, they develop from acceleration. You only feel forces in a car for instance when it speeds up, slows down or turns. If you are driving at a constant speed of 100 mph you will feel no forces from that velocity. The only forces on earth when you are motionless on the surface is the gravity from the earth. There is gravity from other sources such as the moon, the sun, your car, etc. but they are negligable compared to earths gravity.
Completely wrong. If you are in a space ship that is traveling at 5,000,000 mph and you toss a baseball in the direction of travel at 5 mph the baseball will be traveling at 5,000,005 mph and it will never crash into the ship if you maintain your speed. The ball will continue to move away from you at 5 mph essentially forever.
The orbit of the earth would trace a spiral around the galaxy, but that has nothing to do with momentum or inertia.
jiveabillion
Registered Member
I really don't see how this works. If the center Earth is moving in one direction and you are moving in another because the Earth's rotation, how is that not going to cause acceleration on you towards the center of the Earth?
Yes, I am talking about the normal force. You need to look at a body on the surface of the earth and figure out its momentum. Then you need look at how it would change because of the Earth's surface moving it relative to its center. YOU HAVE TO THINK ABOUT THIS WHILE DISREGARDING THE NOTION OF GRAVITY
I've said this before, I don't know the best words to describe what I am talking about, try to use context clues to figure out what I am trying to say. What I mean is the momentum that we get from being a "passenger" on the earth. I didn't say you would feel these forces. You wouldn't feel them because there is no proper acceleration, no momentum or energy is being transferred. You may me motionless relative to the surface of the Earth, but you are never really motionless. The surface of the earth is a non-inertial reference frame.
Nope, not completely wrong. You would have to toss a baseball in the EXACT direction that the Earth is moving. The Earth is not moving in a straight line and since it is rotating and the resultant vector of it's movement is constantly changing relative to any point on its surface, you would not be able to toss that ball exactly in that direction unless you were standing on something in that exact spot traveling in the opposite direction of the Earth's rotation at exactly the same speed. But then you'd have the atmosphere throwing you off. Do you not see that?