Say we have an object of mass falling freely in a gravitational field [ in the vacuum of space] Question: What governs the speed of that fall? Why is it the speed it is and not faster or slower? Any thoughts or knowledge on the subject would be appreciated...
Things don't fall at constant speed in a vacuum. They accelerate at a constant rate in a uniform gravitational field. Drop something from a height. It speeds up as it falls.
The mass of the object you are attracted to, more correctly the energy not the mass, but mass nearly always is preferred and suffices in equation.
Yes good point, hence earths gravity is given in seconds squared. He should have used rate or acceleration instead of speed.
....Scrub that that is impertinent sorry. It's the DENSITY that governs gravity rate, that's why time stops on a blackholes surface.
Mass is the source of gravity. Take two spherical planets of the same mass, one with twice the volume of the other and hence half the average density, and both will exert the same gravitational force at equal distances from their centres (above the planets' surfaces).
0.5mv^2 = GMm/(r^2) as I remember. I think it would be pretty obvious to QQ that falling objects near Earth accelerate so maybe he's asking why we have g = 9.8 m/s/s. I don't remember the equation itself but g (the local constant) depends on latitude, altitude, and stuff like that. If I wasn't so lazy I'd go look it up on the MIT website.
Good referencing! Im too lazy to check, hence you have been sucessful in elevating yourself above me by picking at my weakests links once again. Good job.
Yea you got to remember that we assume objects are point masses. The formula has been verified countless number of times and nowhere in it does it take into account the density of a mass. All that matters is how far you are away from the center and that you are on the outside of the surface. The object is spherical, too.
Yes I was kind of brain farting, I am aware that it's the distance that you are away from the centre of the mass. I saw that the question was alluding to near surface gravity as the facile 'fall' not 'orbit' was kind of thinking that gravity rate at the surface is dependent on the radius of that body(which is indeed correct) then I started thinking of blackholes(which of course are extremely large masses compressed in an extremely large space) then I sort of flashed up density in my mind.
That's only the simplest case. There's no need to make that assumption. If you want to know the detailed gravitational field of a cube the size of the Earth, it is possible to calculate it using Newton's formula and a bit of computerised calculus. That's because density doesn't affect gravity, like I said.
Thanks guys, sorry but my e-mail notification seemed to screw up and I just realised there were posts to this thread. I guess I may be asking an impossible question, or one that requires very specific solutions. I am asking what governs the rate of fall? Why is it not faster or slower, but to answer this we have to know what gravity is exactly... yes? And I don't think we have that answer yet.....hmmmmm....I am sorry but I realised after I posted the questions that I was possibly seeking currently impossible answers. I understand that certain conditions determine the strength of gravitational pull. I think I am right in saying that this is in a ratio to some other attribute of the mass and distance from that mass involved. However what I am asking is the terrible why question. And that, I think, is my mistake. Why is this rate the rate it is? Why is this constant not faster or slower? Sorts of questions. A bit like asking why is gravity a constant.......what makes it so...? Is there any solid speculations out there?
OK we are alluding earth here for sure, right? So for the purpose of the earth, It's because the mass doesn't change. The more mass - the more spacetime is warped, thus the more gravity. All you've got to know is if the mass is constant and the distance between you and the mass centre is constant - then the gravity is constant. PS this is not speculation, this is factual.
I don't see how there could ever be an answer to the question "Why does the universe work the way it does?" Any potential answer would immediately become part of the laws of nature, and therefore part of the question.
Good response and one that I should have anticipated before posting my questions. I premise my questions on the philosophy that everything happens not just because it happened to be that way but on the premise that it can only be that way. In other words the rate of accelleration is part of a constant that is a constant because it has to be a constant. Not just because it happened to be that way [ like a coincedence ] but simply out of physical necessity. To me something must govern the rate of acceleration absolutely, as it is constant and not open to randomness or chance. The rate is fully determined by factors we have yet to understand. And whilst I think your comment about the answer becoming part of the question is very profound and in many ways true I believe that we can and eventually will know the answers to these big questions, unfortunately not any time soon.... so it seems. For example: There are a few "Push" type gravity theories that seem to accommodate my question reasonably well. But unfortunately I do not believe they have proved their credibility with observation and prediction. Aether theorists are another example that I can think of. [ and discounted for the same reasons ] It is true that any answer must be self sustaining and self justifying and that the answer and the question will merge so to speak. I believe that current formulas for accelerating freefall, of course, must also be fully accommodated by any "new" insights. In fact any new insights must re-confirm those constants shown by those equations, thus self justifying. Another example of this issue of self justification is when the question comes up: "Why is the speed of light the speed it is?" Often the answer seems to be: "Because of the permitivity etc of space [ vacuum ] "What causes the permitivity of vacuum or space to act as a governor of the speed of light?" and so on....... I do believe very strongly that there is a level of physics that has yet to develop or will evolve from our current situation. This, yet to be, level of physics will provide answers to these question IMO.
of course this makes perfect sense. And leads to the question: How does the warpage of space time affect the rate of accelerating in free-fall?
That is a good question and there is an equation R=GE that includes something called a matrix that is represented by R(the distortion of space) which is derived from G(the gravity constant) multiplied by E( which is the energy momentum density). Thus there is proportionality between the matrix(the warp of space) and G(your gravity).
Fair enough, but saying that the laws of nature can only be the way they are implies a more fundamental set of laws that govern physics. What do you do at that point? Do you take these new laws for granted? Or do you ask what determines these laws, resulting in an endless cycle of: "The set of laws L<sub>n</sub> is determined by the more fundamental set L<sub>n+1</sub>" ? But will you accept these factors as self-evident, or would you want those explained as well? Not if its a logical impossibility. In my experience, people who propose alternative theories that "explain" physics do not really accomplish this goal, even setting aside the issue of their credibility. Instead, the theorists just stop asking the "Why does it work that way?" question at some point. I've never heard of these "push" theories, but I can illustrate this point in the case of aether theories. From what I've gathered, Aethro-Kinematics attempts to explain all observed phenomena based on the properties of the so-called "all-pervading aether" composed of particles called "aethons." The aether is postulated to behave like an ideal gas, and allows compression waves to propagate through it in much the same way sound propagates through air. This is where Rado (at least I think it was Steven Rado who asserted all this) stops explaining and starts accepting postulates as self-evident. He doesn't explain why aethons interact with one another the way they do. Why do they bounce off one another when they collide, instead of simply flying through one another. Why do they interact at all? Rado stops here because his postulated behaviour of aethons is basically the same as billiard balls, except on a smaller scale. In other words, the laws governing aethons seem very intuitive and familiar to him, so he accepts them as self-evident and not requiring any explanation. That's not a crime, but given this he's certainly in no position to claim his theory is fully "explained." This is the basic problem: how can anything be self-justifying? The examples you gave aren't really examples of self-justifying theories. They're theories that explain other theories, but they do not explain themselves.
in any given gravity field the rate of fall is constant to ask why is like asking why PI isn't 3 or 4
Helmert's equation is good for calculating the local gravitation field according to latitude and elevation. STD Acceleration of Gravity (g) : 9.80665 m/s^2 Helmert's equation : 9.80616 -0.025928 cos φ +0.000069 cos^2 φ -3.086E-8 h m/s^2 where φ is latitude and h is elevation in centimeter
