Bignose

You've got it backwards, KK. The atmosphere is present due to the presence of gravity, not gravity is due to the presence of an atmosphere. Gravity keeps the atmosphere on the Earth. If atmosphere was the cause of gravity, shouldn't the atmosphere in the International Space Station or on shuttle missions be creating gravity? There is an atmosphere on those spacecraft, but just watch any of the videos from those craft and the people inside are clearly weightless. And, here's why. Pressure in a fluid acts in all directions equally. That is, the pressure at a given point in a fluid pushes up and down and left and right and back and forth all at the same time and all at the same strength. So, the pressure from the atmospheres in the aforementioned spacecraft push on the people in every direction equally. So, even though those spacecraft have an atmosphere, the occupants still are weightless. I can understand your desire to figure out the mechanics of gravity -- it is quite a puzzle that has so far eluded many, many extremely talented scientists. But, I just cannot understand your denial of the fact that there are innumerable experiments that show that the amount of gravity is a function of an object's mass and the distance from that object... and nothing else. Considering the many, many successes using that rule to predict how objects behave, what is the motivation for looking for something else? Successes include being able to predict the motions of the planets/comets/asteroids, launching probes to land on other planets and near other planetary moons and comets, launching satellites into orbit, etc. etc. I almost cannot believe I am doing this, but you should look into the Pioneer Anomaly. This is actually one case where what we thought we knew and we predicted was not what was observed. Some of the deep space probes have had some small unknown forces acting one them. And one of the many possible explanations is that Newton's Law of Gravity may not be exactly 100% right -- that for accelerations under 10^-10 m/s^2, there may be a different form of Newton's Law that applies. But, there are many other possible explanations too, including errors in the mass of some of the objects in deep space (like the Kuiper belt), our incomplete understanding of dark matter, the spacecraft itself may have had a slow leak of a gas, the solar wind, or maybe even incomplete communication and simple statistical error. We may never know for sure, but there are lots of possibilities, and compared with the millions of successful predictions Newton's Law of Gravity has been used for, a few tiny errors on a few deep space probe is no reason to toss out or radically change Newton's Law like you are promoting including rotation into the Law.

Besides Tom's proof (which was very nice), I really, really liked the tree's visualization of the concept. Multiplying by a negative is a reflection, so multiplying a negative by a negative is in effect the reflection of a reflection which would be the original back again.

gravity is a force and a force is proportional to acceleration. Force is equal to acceleration times a proportionality constant. Saying "contains gravity but does not contain any type of accelerating force" is completely meaningless. If there is gravity, that means there is a force; and if there is a force that means there is acceleration. This is one of the very most basic definitions of physics. If you are having trouble with this, please go and read and Introduction to Physics book. Your library should have several to choose from.

insane_alien is referring to that most basic of physical laws [math]F=ma[/math] F = force m = mass, and a = acceleration Simply put, if there is a mass, there is a gravitational force associated with that mass. And force is proportional to acceleration. If there is force, there is acceleration, no matter what the force is from. Drag, friction, rocket boosters, or gravity.

Then a more accurate theory will replace the one we have. At its very core, science if very objective. If a new theory comes along, explains everything the old theory does, predicts new things the old theory didn't, or predicts things better than the old theory, and there is sufficient evidence that the new theory is more correct the new theory will be adopted. Science is objective in that a theory is measured by how well it predicts phenomena. If a new theory predicts better or more than the old theory, the new theory is considered better. It really is that simple. But, science is also objective in rejecting speculations without evidence, such as the one you presented in this thread. There is no evidence that rotation of an object affects its gravitational force, so science rejects that claim. It is all about the evidence.

While I do believe that mankind's influence is a significant contributor to GW, there is plenty of scientific evidence that at least questions mankind's role. There is a good collection at http://www.worldclimatereport.com/ They take articles out of peer-reviewed scientific journals that do indeed raise doubt about mankind's influence and summarizes those articles. Like this one: http://www.worldclimatereport.com/index.php/2007/05/14/questioning-ocean-warming/ that discusses a very recent paper that compares 50 years of ocean temperatures. Note that some parts of the ocean warmed and some parts cooled and the authors of the paper feel there was no systematic warming or cooling. Compare that with all the hype about how hot the oceans are getting, and the actual data record is eye opening. I know that the site has an agenda, and it is largely funded by companies that have the same agenda against anthropomorphic GW, but I really like the site since the popular media only seems to report about the scary and very pro-anthropomorphic GW studies and never about the ones that use good science to dispute it. I think that both sides of this debate need to be reported and that one side has a monopoly. The other side has scientific papers written too, and I like to see them as well as the ones reported in the popular media.

Well, CPE, I think that you started this with your comment "to prove their superiority". At least for me, that's why I felt the need to reply again. Because, there is a fundamental difference between speed and velocity, and if you don't have any problems distinguishing them that is great. But, the average physics student does, and emphasizing that difference and making sure the difference is clear right from the start builds a strong foundation upon which to build the rest of the physics knowledge. The language of physics is meant to be exact. If you say "speed" then you mean one thing that is different than saying "velocity." These words are defined exactly so that their meaning is clear every time you use them. This is the preciseness that hotcommodity is talking about. It has nothing to do with ego, or "proving one's superiority". It has everything to do with being clear and using the words as intended and not blurring their definitions for someone who is not as familiar with their uses as you or I. It is fine that it is your opinion that "speed" and "velocity" aren't different, and it is fine that many of the rest of us think that they are significantly different. And many of us probably are not going to budge in our opinions that they are significantly different. I don't think we, and I know myself, that we aren't "eager" for a fight, it is just that we are trying to be as clear as possible. Insane_alien's example was great about a particle zipping around a circle quickly. It shows very clearly the difference between speed and velocity, and many of us think that that is a very important distinction to make. If that is "eagerness" for a fight, we then I guess that's that. But, I (and I think the rest) are just trying to make sure that any beginners or new students to physics makes sure that they understand the very fundamental difference between speed and velocity. That's all.

Good gravy, CPE! swansont maybe didn't want to speak up here, but I'm going to speak up for him... in no way was swansont trying "to prove their superiority" because there is a very significant difference between vectors and scalars. My personal opinion is that swansont wasn't trying to prove anything except that getting the fundamental's right forms a much more solid foundation for future learning. The specific components of a vector transform depending upon what corrdinate system is being used. Scalars don't. Consider starting with a 2-D Cartesian coordinates and let's observe a particle moving along the x-axis at 1 m/s. In this case, both the speed and the x-compnent of the velocity is 1 m/s. But, now, let's rotate the coordinate system 90 degrees. Now, the velocity is in the y-direction, but the speed is exactly the same. But the velocity is very, very different. Now, let's rotate the coordinate system 45 degrees. The speed is still 1 m/s, but now both the x and y coordinates of the velocity are 0.707 m/s. Very different indeed. In no way would I call this difference "slight". This doesn't even cover if you wanted to describe the velocity in cylindrical or spherical or bipolar coordinates or any other coordinate system. But, no matter what coordinate system you use, the speed being a scalar remains the same. swansont's point here is that the language of physics includes vectors, and different coordinate systems, and that knowing how they work properly is fundamental to knowing physics properly. CPE, I'd suggest you do yourself a favor and read one of the many good texts on vectors, like Schuey's Div, Grad, Curl and all that to learn just how different vectors are from scalars.

It is inertia. An object in motion continues along the same line at the same speed until another force acts on it. So, consider being on the inside of a spinning ring. You are moving along sideways because of inertia, but because the floor is moving around in a circle, the floor gets in your way and turns you in just a little. Well, now inertia moves you along that slightly different line, but again, another bit of floor gets in the way and turns you again. Repeat over and over. If the ring is large enough, the floor won't have a very significant curve to it, but because inertia keeps forcing you to run into the floor, this running into the floor mimics the force of gravity. Hence, you get an "artifical gravity" And, yes, this sort of system can be used to mimic gravity for longer spaceflights or habitation of space stations. The first act of Kubrick's film 2001 has a great example of what one such space station could look like. http://carriedaway.blogs.com/carried_away/2005/03/2001_where_are_.html Look at the second picture on that guy's blog.

The X =d normally means "X is distributed according to" and the R would be the probability distribution. But, I am unfamilar with what R would mean, too.

There aren't "types of gravity" There is gravity which is a function of mass, and then there are ways of mimicing gravity termed "artifical gravity". But, mimicing is not the same as being. I can mimic Albert Pujol's baseball swing, but sure as heck cannot hit home runs like him. I can mimic Tiger Wood's golf swing, but sure as heck cannot hit 300+ yard drives. I can mimic President Bush's voice, but that doesn't make me the President. See what I am saying -- just because there are ways of mimicing gravity, doesn't make them gravity. In this case, the mimicing of gravity is caused by being flung outward by the spinning. If you spin at just the right speed, that flining can feel exactly the same as 1 Earth's gravity. But, we don't define forces by how they feel. And just because the flinging from being spun mimics gravity, does not mean that it is gravity. Also, you never answered my questions... "If rotation were important to the gravitational force, shouldn't there be a term (in Newton's Law of Universal Gravitation) for the period or speed or angular momentum?" and if you had any evidence that simply spinning would change the gravitational effect of an object. Ideally, this would be two seperate experiments -- The first experiment measures the gravitational force between two objects both of which are not spinning at all, and the second measures the gravitaional force between those two exact same obejcts one of which is spinning. If you perform this experiment and the gravitational forces are different, then you have the evidence to support your theory. But, right now, there is no evidence to support your idea at all, which means as far as we know, it is wrong. I'm sorry, but without evidence, your idea is wrong. Period. Edit: I just wanted to reply a little to ecoli's post there, which brings up a great aside. While there are mountains and mountains of evidence that support Newton's Law above, which means science has a very good grasp on how gravity behaves. Meaning, in terms of using Newton's laws for predictions it is great -- we know how to launch probes to fly next to and take pictures of comets, and know how to launch probes to land on Mars, etc. etc. However, sceince does not have a very good grasp on how gravity works. I.e. the graviton has been proposed, but has never been confirmed measured. Which means that there is much uncertainty on how gravity does what it does. But, we know what gravity does and what affects what gravity does (i.e. the masses of and the distance between objects), and it does not include whether one or both or neither of the objects is spinning.

No, Newton's law predicts exactly the same gravitational force, whether the obejct is rotatng or not. Look at the equation again, there are no terms whatsoever for rotation. If rotation were important to the gravitational force, shouldn't there be a term for the period or speed or angular momentum? Look, Venus' mass is pretty close to Earth's (Venus' mass is 82% that of Earth's), as is it's diameter (95% of Earth's). If you could walk around on its surface, the force of gravity pulling you to the surface would be pretty close to the same as on Earth. Just to put a number to this discussion, you would weigh about 90% of your Earth weight on Venus. But, Earth rotates on its axis once a day, but Venus rotates on its axis once every 243 Earth days. The fact that Venus rotates significantly more slowly than the Earth does not change the fact that the gravity on Venus' surface is pretty close to Earth's. Gravity is a function of an object's mass, not it's rotation. I am aware of no evidence that has ever shown gravity to be a function of rotation, if you have some to present to substantiate your theory, I'd much like to see it. However, like I said above, Newton's Law of Universal Gravitation has been tested over and over and over, and it comes up correct every time. It's going to take a lot of really good evidence on your part to overthrow it.

Erm, no. Let's look at Newton's law of universal gravitation: [math]F=G \frac{m_1 m_2}{r^2} [/math] F is the magnitude of the gravitational force between the two masses G is the gravitational constant m_1,2 is the masses of the 1st and 2nd objects, respectively r is the distance between the two masses This theory has been validated time and time again. Where exactly is the "some type of rotation going on"?

This specific sentence, right here, is what I'd like to see evidence of. And, yes, I treated the card as just a rectangle. It was only a comparison between the angular momentum of a card (considering its mass, size, and speed) compared with a saw (and it's mass, size, and speed) Actually, looking at that quote I quoted, I am curious why you consider spinning to be different from lateral movement? Either way, the edge is moving at 155 mph, the same speed means that the penetrative power is the same, and a card embedded in flesh would probably come to rest pretty quickly, so i don't think that the spinning isn't going to make a lot of difference anyway. I think that spinning would only change the way the card embeds in the flesh, not the depth it embeds. As much as anything, the problem with your theory is that a card is only 2 grams of mass. Compare that with a poker card sized sheet of aluminum or lead -- much more mass and hence momentum & energy behind it. You have to get something very light moving very, very fast to have a lot of momentum and energy.

OK, so your guy did some work with an architect. Can you debate or answer any of the many valid questions insane_alien brought up in post #39? Such as the insistence that the steel had to melt when much evidence has been cited that shows how much strength is loses just from being heated up. Can you address these questions, please? If you can't address these questions, can you drop your claim? (p.s. I'm not holding my breath for that last one)

bored_teen. I understand that you have a theory. I disagree with your theory, and I went into detail to explain why I disagree. What I would like is some concrete objective evidence (again, like a video, or some order of magnitude calcuations) from you that supports your theory. If you have none, then we have to begin to seriously doubt the validity of your theory. Not to put too fine a point on it, but this is a science forum and this process of providing objective support for a theory is exactly how science works. So, can you provide any evidence?

Can you cite any scientificly determined proof for this (as this is a science board)? You really need to justify a statement like this with some sort of proof/evidence. Like, an order of magnitude calcuation or a video or something... For example, here are some order of magnitude calculations: For a "buzzsaw" I looked up "mitre saw" in google and used the first one I saw (I think it was on Home Depot's webpage). It was a 12 inch saw which spun at 3800 rpm, and the saw blade was 2.8 lbs. The moment of inertria for a spinning disk is [math]I = \frac{1}{2} m R^2[/math] R = radius of the disk = 0.1524 m m = mass = 1.27 kg So, the moment of interia for a saw blade can be calculated as equal to 0.0147 kg m^2 Multiply the moment of inertia by the angular velocity and you get the angular momentum. The angular momentum is important since that is the momentum that will have to absorbed to stop the blade or card. So, 3800 rpm times the perimeter of the blade means the blade spins at 3638 m/s. Mulitplying that all together, the angular momentum of a saw blade is 53.665 kg m^3/s Now, let's look at a card spinning at 155 mph. The moment of inetria of a rectangle is [math]I = \frac{1}{12} m B H^3[/math] where H>=B (H is the longer side). Poker cards traditionally are 2 1/2 by 3 1/2 inches, and a deck of 52 cards weighs about 100 grams, so 1 card is about 2 grams. So, calculating the moment of inertia of a card (and converting the untis to metric), I estimate I_card = 7.4358 *10^-9 kg m^2 multiplying this by the edge speed of 155 mph (69.29 m.s) the angular momentum of a card can be found to be: 5.15 * 10^-7 kg m^3/s Or, in other words, a saw blade has over 100 million times more angular momentum than a playing card spinning at 155 mph. I can confidently say that your statement "in essence turns a card into a flying buzzsaw" is quite an exaggeration. But, maybe you are right. That's why I'd like to see some objective proof, and not just take your word for it.

Or an Introduction to Physics text? I am positive your library has several to choose from.

Here I had hoped that the "WTC couldn't have been weakend by fire" crowd would have disappeared after that bridge in California collapsed due to a gasoline truck fire. http://www.cbsnews.com/stories/2007/04/30/national/main2740065.shtml If one little tanker truck full of gasoline can collapse two overpasses, I have no problems whatsoever believing an entire jet liner full of fuel could have easily taken down buildings.

You are also forgetting all the means of determing what is underground available to us. Take registering an earthquake. The most accurate detectors can detect earthquakes quite far away, i.e. detectors in the US detecting the quake that caused the 2004 tsunami. In order for those detectors to work, we have to know how the waves travel through the earth, meaning we have to know what the earth is composed of. Otherwise the detectors wouldn't work right. In fact, intentionally causing waves to form in the ground has allowed scientists to map out the entire crust of the earth to several hundred kilometers. They can locate convection cells and mantle plumes, using this method. As far as I know, no large voids have ever been found. Sure, there are cave systems, but I think you are talking about voids thousands of kilometers large, and I don't think that voids that big exist. For example, http://en.wikipedia.org/wiki/Mammoth_Cave_National_Park says that "if connections are found between the three giant caves ... the total mapped system would exceed 800 km" That is, if connections were found between some of the largest caves in the US -- and they haven't yet -- it still would add up to be pretty small on a global scale at 800 km. Compare that with the Earth's diameter of more than 12,000 km. Your particle (<-- note the correct spelling), in a hollow earth would not be pulled anywhere. Again, inside a uniform hollow sphere there is no gravity at all. The pull from the shell sums to zero at all points inside the shell. This is a classic mathematical result. Finally, RE: "Not that I am correct but my argument sounds valid to me." there are lots of people who want to make arguments that "sound" good, but fall short in terms of facts. Arguments and debates are NOT decided on what "sounds" the best -- despite how almost every politican acts or how almost every advertisement tries to sell to you. When you look at the established facts and evidence, the theory that the earth is not hollow is overwhelmingly supported by the facts while the theory that the earth is hollow has very little facts to support it at all.

Scientists are pretty sure there is something in the middle of the earth if only because the mass of the earth is known, and the density of earth is known, so that space pretty much has to be filled. Also, I think you are misapplying the no gravity in a hollow sphere rule. Everywhere on the inside of a uniform spherical shell there is no gravity. Your example of the particle 2 miles off center isn't right. Yes, it is closer to one side so that one side has a stronger pull, but there is more than just half of the shell on the other side. That more than half is farther away, but being that there is more, it exactly cancels out the closeless of the lcose side. Hence, everywhere inside a hollow sphere has no gravity.

Ok, thus spurred a few calcuations, since I was interested what the numbers actually said: First, I used Google scholar to find the average mass of an ant. Since there are many, many species of ant, I found info on the leaf cutter ants and found that the workers were as small as 1.4 mg to 32.1 mg. Leaf cutter ant's head width also averaged between 1.4 and 1.6 mm (depeding on what colony of ants was studied). So, for calculation purposes, I assumed an ant was three spheres, the total width of the head at 1.5 mm, the middle 3.0 mm, and the back section 3.0 mm. So, taking the mass of an ant as 20 mg and divind that by total volume of those three spheres, the density of this ant is 665 kg/m^3. Do ants float on water? Their density is less than water's 1000 kg/m^3, but I don't know if they float or not so I don't know if this is a good guess or not. Anyway, then, for calculation purposes, I treat the entire body of the ant as a single sphere. I added up all the volume, then calculated what the radius of the sphere that has that same volume as the entire volume of the ant. So, that mens I treat the ant as a single sphere with radius 1.9 mm (or total width of 3.8 mm). The question here is what terminal velocity an ant reaches. This is obviously a difficult question, since what the terminal velocity is is dependend on what the drag force is, but the drag force is dependend upon what the velocity is, meaning you h ave two unknowns (drag force and terminal velocity). Normally, you'd have to use two equations and solve for two unknowns, but correlations exist for estimatig these numbers rather than trying to solve two simulataneous equations. The first correlation to use is to calculate the Archimedes number: This is a number that is independent of the terminal velocity [math]Ar = \frac{d_p^3 \rho_f (\rho_p - \rho_f) g}{\mu^2} [/math] [math]d_p[/math] is the diamter of the particle [math]\rho_f[/math],[math]\rho_p[/math] is the denisty of the fluid, particle respectively. The density of air is 1.246 kg/m^3 [math]g[/math] is the acceleration due to gravity = 9.8 m/s^2 [math]\mu[/math] is the viscosity of the fluid = 1.78*10^-5 kg/(m*s) Plugging these numbers in yields an Archimedes number of 1.4*10^6 There is a correlation between the Archimedes number and the Reynolds number at terminal velocity. But first let me define what the Reynolds number is: the Reynolds number of terminal velocity is [math]Re_t = \frac{U_t d_p \rho_f}{\mu} [/math] where [math]U_t[/math] is the terminal velocty, and all the other terms are defined above. The correlation between Ar and Re_t is: [math] Re_t = (2.33 Ar^{0.018} - 1.53 Ar^{-0.016} )^{13.3} [/math] Plugging in the value for Ar above, I get a terminal Reynolds number of 2299. In physics terms, the Reynolds number compares the relative magnitudes of the inertial forces versus the viscous forces in the fluids. If the Reynolds number is very high (10^5, 10^6 or higher), the inertial forces dominate. If the Reynolds number is small (1 or less) the viscous forces are very important. This is important since if inertial forces dominate, the shape of the object is the primary determiner in how much drag it will experience. If viscous forces dominate, the surface properties (like it's roughness) are the primary determiners of how much drag the object will experience. I find it interesting that in this case, the Reynolds number is in that intermediate region. To put it simply, both the inertia and the viscous forces are important. Then, back calculating for the terminal velocity ([math]U_t[/math]) I get a terminal velocity of 8.5 m/s Compare that with the terminal velocity of an unparachuted human skydiver, which is about 56 m/s, you see that a human falls 6 1/2 times faster. Because of this higher velocity, the Reynolds number for a person is much higher than that of the ant, in the tens of thousands. That high of a Reynolds number means that the inertial forces are dominant. Or, in other words, the surface properties are not important -- or in other other words, you can't significantly change your terminal vleocity whether you were wearing a wool sweater or a spandex body suit or whether you had shaved or not -- none of that matters when skydiving. My calculations for the ant are probably riddled with error. Firstly, assuming a sphere is a worst-case lowest drag scenario. The fact that an ant is actually three sphere-ish segments will increase the drag a fair amount. Also, the legs and antenne have to increase the drag somewhat too. Nevertheless, I think that the calculations are insightful in that it is obvious that an ant falls significantly slower than a person does. Couple that with their exoskeleton, and I think that explains a lot of why an ant can survive that level of fall compared with people.

Here are some hints. The given acceleration is enough information to locate where on the circle the purse is currently located. You will need this to locate where the wallet is. And, the amount of acceleration of a point for rigid body rotation is a function of the distance from the center of rotation. Obviously, the center of the merry-go-round has no acceleration since it isn't going anywhere, and the edge is accelerating a lot. You should be able to figure out or look up in your text what the relation between distance and acceleration is.

Well, firstly, you should have some software that can compute these numbers for you. Both Excel and Windows calculator can calculate these numbers ... 9^5 + 8^5 = 1934927632 whereas 72^10 = 3743906242624487424, clearly not the same. However, 72^5 = 1934927632. If and only if the exponents are the same, you can mulitply the bases: 9^5 * 8^5 = (9*8)^5 = 72^5. But, if it is 9^4 + 8^5, there is no simplification possible.

It is a classical assumption from fluid mechanics that the fluid immediately next to a solid object has the same velocity as that solid object. Usually, this is used to set the fluid velocity to zero at a pipe wall, but the reverse is also true. The fluid, air in this case, near the earth's surface is moving at the same velocity as the earth itself. Of course, we are moving too, so relative to our point of view there is no movement, but the air and everything, including the clouds, is moving together.