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gravity

Gravity (from Latin gravitas 'weight'), or gravitation, is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light—are attracted to (or gravitate toward) one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the tides of the oceans. The gravitational attraction of the original gaseous matter present in the Universe caused it to begin coalescing and forming stars and caused the stars to group together into galaxies, so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, although its effects become weaker as objects get farther away.
Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915), which describes gravity not as a force, but as the curvature of spacetime, caused by the uneven distribution of mass, and causing masses to move along geodesic lines. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon. However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them.
Gravity is the weakest of the four fundamental interactions of physics, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a consequence, it has no significant influence at the level of subatomic particles. In contrast, it is the dominant interaction at the macroscopic scale, and is the cause of the formation, shape and trajectory (orbit) of astronomical bodies.
Current models of particle physics imply that the earliest instance of gravity in the Universe, possibly in the form of quantum gravity, supergravity or a gravitational singularity, along with ordinary space and time, developed during the Planck epoch (up to 10−43 seconds after the birth of the Universe), possibly from a primeval state, such as a false vacuum, quantum vacuum or virtual particle, in a currently unknown manner. Attempts to develop a theory of gravity consistent with quantum mechanics, a quantum gravity theory, which would allow gravity to be united in a common mathematical framework (a theory of everything) with the other three fundamental interactions of physics, are a current area of research.

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  1. E

    gravity fed upstairs shower pressure question

    We have a gravity fed hot water system in our the house we have just recently moved into. It works fine with the downstairs shower, however we are about to upgrade the upstairs bathroom and are considering installing a shower bath. My concern is that although there is more than sufficient...
  2. S

    Gravity or mains shower?

    I have a dead 1990s Triton T70 shower and, for purposes of replacement, I'd like to know if it's mains or gravity fed. As it won't even switch on, I cannot get any water out of it so I can't just switch off water at mains and see if water still flows from the shower. I note that current Triton...
  3. F

    Wood Burner back boiler with gravity rad system.

    Hi All...thx for the help in advance. I have recently installed a wood burner with back boiler heating system. Set up with gravity rad and header tank in loft. I have a recirculation pump installed that I have connected to the rad system that I turn on and off manually. I wanted to know how...
  4. M

    hot water gravity slows to nothing

    Hi, My gravity fed hot water slows to nothing over 30 seconds. when tap turned off for 5 mins, tap will run again for 30 seconds etc. I have tried the mixer tap/air lock trick about 10 times now and still not fixing. I have drained the HW tank a little so I can inspect the 22mm out pipe at...
  5. C

    Using combi fed and gravity fed showers simultaneously

    Hi all, I have a combi boiler for hot water and heating but have 2 showers in the house. Obviously low water pressure if both showers are used at same time. I'm wondering if I could install a water tank to gravity feed one of the showers, with new electrric shower and if so how to stop the water...
  6. F

    Blended hot outside tap from gravity

    Customer wants an outside tap for dog washing so needs to be blended. The hot water is gravity and its a bungalow so little head at the point of installation. I can't get a cold from the storage cistern to the utility so it has to be mains cold. Can pressure reducing valves be taken down to...
  7. N

    Tap for a gravity based hot water system

    Hi, I have a gravity based hot water system, and recently had a new kitchen installed. We never had a noticeable hot water pressure issue before, but the flow from the new tap is down to a trickle. Pressure head is c.3m. Flow is 2L/min compared to 12L/min minute out of the hot water tap...
  8. A

    Thermostatic Mixer shower can be fitted to Mains and Gravity Hot?

    Hi all, I've been researching and planning a job for my home the past few days and a few pieces of advice would be welcome to help me along the way. I have a cloakroom toilet which has a toilet and a sink, where the sink currently is there is good room to put a small shower cubicle and a...
  9. I

    Why is there a blue and a red float for a FOP on a gravity fed tank?

    I assumed that the red ball float was for a header tank on the central heating side and the blue ball float was on a cold water storage tank. I thought the reason for this was only to help identify the tank but after finding a lot of cold water storage tanks with a red float, I must be wrong...
  10. K

    Gravity feed hot water tank

    I’m fitting a ‘gravity feed’ hot water tank in a mobile home that has restricted head height for a cold gravity feed header tank. I can install an expansion over flow to an outside drain. Is it possible to use a Pressure Reducing Valve to supply the cold water from the mains supply. Or is there...
  11. G

    Installing decent pressure shower on a gravity fed system

    We currently have an electric shower fed with mains cold this mains cold is really bad pressure coming into the shower resulting in really poor pressure from electric shower. We have a gravity fed system what's the best and cheapest way to get a decent pressured shower fed from our gravity fed...
  12. D

    Greywater Gravity Drain Problems

    Hey guys, I live in Arizona where it is hot as blazes and water is scarce. I made a DIY gravity drain system to reuse water from my washing machine to water my trees. Below is a really well-drawn sketch (haha) of the setup. My problem is that little to no water comes out at the tree! I already...
  13. L

    How can i turn my standard gravity loft fed system

    Trying to get a high pressure shower running off a gravity fed system
  14. W

    Mixer shower - mains cold - gravity hot

    Hi, I've seen a few posts about not using mains cold with gravity fed hot. Ours is only about 0.1 bar for the hot. The reasons given vary from possible backflow into hot cylinder to hard to get a good mix. In that case how does the kitchen mixer tap work - that mixes gravity hot and...
  15. D

    Gravity or mains fed shower?

    I’m replacing my faulty old mains fed electric shower (Mira Sport Max 10.8kW) and am considering going for a pumped, gravity fed electric shower (such as the Mira Elite SE Dual Pumped Electric Shower 9.8kW). The mains pressure sometimes drops enough for the low-flow cut-out to operate or the...
  16. A

    Switching from Gravity to fully pumped - open vent position?

    Hi, Our gravity HW tank split and without a long delay the only one we could get was a fully pumped tank. Fairly easy replumb to get the tank in, however on all diagrams I've looked at, the fully pumped system has the open vent coming off between the boiler and the pump, whereas in our current...
  17. E

    How can I get heat into Gravity Fed UFH system

    Hi folks, I’m in need of some sound advice. We have recently had a ground floor extension and have had underfloor heating (company: JK UFH) installed throughout most of the downstairs. We have a few rads still left downstairs and the entire upstairs is still heated through rads. We have a...
  18. A

    Gravity heating system question

    Hi all I’m curious about the conversion of my heating system I have a gravity system with no diverter valves, the cylinder is quite small and there is an air separator present I am curious as to how this system would be converted to a combi system, am I right to assume that the flow and return...
  19. O

    connecting ejector (pressurized) to secondary / gravity main line

    question about connecting an ejector pump to the sewer, where there is no existing conditioned structure that gravity-feeds: We have a lot that will be built in a couple years. Lot is sloped, with road and sewer main nearest to the up-hill lot line. The house will built in that corner, and...
  20. J

    NIGHTMARE GRAVITY SYSTEM!

    All, Need some ideas pleaeses and thanks. Customer had drained system and had awful air locks, went round boiled out and got working... GREAT! 2 weeks later after some bumping and banging, no hot water. Went round and flow red hot, nothing on the return. Boiled again... Got hot water...
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