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Energy through gravity?

I know that this question has been dealt with before.

But I'm going to ask it in a different manner:

If we look at all the planets, stars, asteroids, galaxies and so on.
They are all somehow under the control of gravity.
If it is gravity that makes them move in their respective way,
is not then gravity a force by itself? And thereby, there is a source of energy behind that force?

My question/idea is simple: If everything in the universe is put in motion by gravity, shouldn't there be a way for us to "harness" that force and energy?
Can you imagine the amount of energy we could use?

  • Jan 29 2014: Of course this is true and such ways of harnessing theenergy from gravity is in fact being done all the time. To put it simply anything which is lifted up higher in a gravitational field, e.g. picking up a stone from the ground, will possess potential energy. This is energy which is not yet being used. But you let go of the stone and it will fall and hit the ground. It has now started to use some of its potential energy, in fact that energy has been converted to kinetic energy or energy of motion. THis basic principle is used all the time in harnessing energy from water which is held in dams, so called hydroelectric schemes. The damstops water from flowing down a river and it builds up into a deep lake behind the dam. Then you control the release of the water through pipes built into the dam. The pipes fill with water and it rushes down and pushes some turbines which have been placed in the right place to allow the water to push them. The turbines turn and through the generator effect in electricity start to make electricity which can then either be inserted into the electricity grid or stored in some way in batteries.
  • Feb 4 2014: Understanding orbit: Imagine you fire a gun parallel to a flat plain from 2 meters off the ground. How long will the bullet stay in the air? If the bullet travels 250m/s, how far will it go?

    Distance traveled under constant acceleration = starting velocity * time + acceleration * time ^ 2 / 2

    Initially, it is falling at 0m/s, then gravity accelerates it toward the floor at 9.8 m/s/s, distance is the 2 meter fall.

    Substitute in known: 2 = 0*t = 9.8 * t^2 /2
    Eliminate the 0 term and multiply both sides by 2: 4 = 9.8 t^2
    Divide both sides by 9.8: 0.4 = t^2
    Square root both sides: 0.6s = time

    So, if the bullet were fired at 250 m/s, and took 0.6s to hit the ground, it will have traveled 150 meters down range.

    Over 150 meters, the curvature of the earth is negligible. Over that distance, a "flat" plain really is flat.

    Now imagine firing a cannon 2500 m/s from an airplane 2000 meters off the ground. (ignore wind)
    4000/9.8 = t^2
    time is about 20 seconds and then distance traveled down range would be 50 kilometers.

    Over that distance, the earth is NOT flat! Over that 50 kilometers the earth's curvature is about 400 meters. The distance the projectile has to fall is 2400 meters, not 2000. Artillery gunners do have to adjust for the curved earth. The earth is falling away as the projectile flies over it.

    Imagine firing a bullet 200km/sec. Even if fired from 2 meters off the ground, the 2 seconds the bullet took to fall, it will travel 400km. Over those 400km, the curve of the earth would drop the surface 3km away. So, the earth is falling away faster than the bullet can fall.

    Now put the the projectile 400K km up. The fall of the bullet from gravity bends its path just enough so that it makes a complete circle and ends up back at start.

    That is the moon. Always falling toward the Earth, but is traveling so fast in a direction perpendicular to where it needs to go, that it just ends up going in circles around the Earth.

    Same for the Earth and our sun.
    • Feb 5 2014: Great explanation, thank you. I'm trying to understand these basic concepts which according to me are neglected by teachers in high school and such. I've learned how to calculate similar problems but not really understood WHAT I am calculating... So the "bending" that the object makes on gravity keeps it in motion, and because of the great speed in which it is traveling...

      I'm thinking, wouldn't it be possible to somehow create this motion by putting two objects in space in motion with relation to one another; one with greater mass, so that it imitates the moon/earth or earth/sun gravity pull? And from that motion, you build a generator of some sort that is able to "collect" the energy from that motion? You would need two objects with an almost improbable mass, as great as the earth/moon?
      Wouldn't it, in theory, mean that you would get an infinite amount of energy from that motion?
      • Feb 5 2014: You are trying to violate the law of conservation of energy. Can't do it.

        It would take energy to put the objects into motion. Then, by harvesting the energy back out, you would have to be slowing the objects back down. In the end, we can not get more energy out of the motion that we put into it.

        Again, we cannot harvest work from potential difference, without reducing the potential difference.

        High pressure here and low pressure there. We can harvest work by allowing air to flow, reducing the pressure on the high pressure side and increasing it on the low pressure side... We then have to use energy, like burning coal or fissioning uranium to recreate the pressure on the high pressure side.
        • Feb 5 2014: But for some reason, the objects in the universe seem to have infinite energy. Because of what you have already told me about the gravity pull of planets and so on. So by what we know today, all of these objects in space are still in motion because of the left over kinetic energy of the big bang? Or maybe knowledge on "dark energy" will shed light on this question?
  • Feb 1 2014: We do. Since prehistoric times we do.
  • Jan 29 2014: It's called a "water wheel". That's the most practical way to do it. It's a combination of solar and gravity. The sun evaporates water, which condenses into rain. The rain feeds rivers. Rivers flow downhill due to gravity. A water wheel can extract some of the energy of that movement. It's been done for thousands of years.
    • Feb 2 2014: actually, a turbine, like used I... you know. Hydro-electric power plants, is an even more efficient way of capturing the potential energy of water due to gravity. Water wheels are good (60%-70% max efficiency) but the turbine can exceed 90% efficiency pretty easily.
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    Feb 10 2014: Do you mean we can do something with what we detect as the universal gravity forces in space?

    Gravity has been used on earth, intentionally or instinctively in all digging, processing and constructing. (We know- Gravity is an unavoidable force of nature keeping our bodies and our homes in one piece, at least for awhile.)

    But I have this very specific question, before one thinks about where to get more energy - can one explain:

    WHY DO WE NEED SO MUCH MORE ENERGY WHILE WE WASTE AND MISUSE SO MUCH ENERGY ALREADY AND QUITE STUPIDLY?


    Can we rethink our Reasons? Do we need to increase traffic, mass-produce more junk products, build more fancy "defencive" war-toys, fill the skies with more jets?

    Innovative systems, which can intelligently support our sustainabily, are already available, sustainable heating and cooling, water and sewage systems, as well as production of earth friendly materials and textile, and some technology that is not harmful for organic gardening and safe environment... this list is ENDLESS.

    I think what we REALY desperately need is to re-design and drastically change our urban infrastructure, road systems, and decrease dependency on major suppliers, therefore, illiminate heavy commercial traffic in residential areas and across the country.

    Learning about sustainability would not cost us a fortune - this will create meaningful and greatly rewarding new jobs, and inspiration for the young.
  • Feb 5 2014: Law of conservation of energy. Energy is never created (since the Big Bang) nor destroyed. It is only transformed from one form to another.

    It doesn't take energy to keep an object in motion. It only takes energy to accelerate or decelerate the motion.

    Gravity is constantly accelerating the moon in a direction perpendicular to its current motion, but only by accelerating the Earth in the opposite direction. The Earth is 81 times as massive, so the acceleration of the earth is 1/81 as much as the moons, but the total energy change of the two exactly cancel each other out.

    When the moon reaches the other side of the earth, it tugs it back, reversing the acceleration. In effect, the orbit of the moon pulling on the earth (but not changing the total energy of the sum of motion of the two objects) causes the earth to wobble.

    The earth, orbiting the sun, causes the same to happen to the sub, ever so slightly. This wobble is actually one method of finding planets around very distant stars.

    So... the earth moves the moon and the moon moves the earth, transferring energy between them, but the sum of all energy is not reduced.

    Only when one is accelerated or decelerated more than the other, as in the case of the moon deforming the earth's shape, slowing the moon's motion in the direction of its travel, is energy transformed into heat (via friction in the Earth's deformation).
  • Feb 3 2014: Thank you all for your answers. But my main point has still not been answered. What is it that puts everything in the universe on the move, in motion? Is it just the "left-over" kinetic energy from the big bang, like Mr. Darrell Shimel Jr. said? Or can there be some kind of energy, still there, that "pushes" the planets and galaxies on?
    • Feb 4 2014: This is basic Newtonian laws of motion.

      http://csep10.phys.utk.edu/astr161/lect/history/newton3laws.html

      Pre-Newton, the prevailing assumption is that things 'slowed down' on their own. Roll a ball, and eventually it stops. Newton explained the ball was being effected by forces that were slowing it down. Wind resistance, rolling resistance from being misshapen by gravity, etc.

      That is the first law. Bodies maintain their current state of motion unless acted upon by a force.

      Thermodynamics says the friction turns to heat, and Law of Conservation of Energy says that the creation of heat via friction slows motion.

      There is no wind friction in space. There is, however, the equivalent of rolling friction, to a point. Due to gravity, the moon pulls on the Earth as it orbits, creating tides, tectonic forces (resulting in earthquakes) and slight misshaping of the earth. That misshaping generates heat, which is what keeps the earth's mantle molten hot. The generation of the heat actually slows down the moon.

      Or, Newton's 3rd law of motion. As the moon tugs on the Earth via gravity, the Earth is tugging back. Due to the misshaping, the tug is ever so slightly off the perpendicular to the tangent of the orbit. That slight asymmetric tug slows the moon.

      So, in addition to hydro-electric being harnessing gravity's pull on the water, so is geo-thermal, harnessing the heat generated by the moon's gravity tugging on the Earth.

      In both cases, it is not the potential difference that is used to create work, but rather, the resolution of the potential difference. The moon slowing, the water moving down.

      All the above said, the galaxies appear to be speeding up in the rate at which they are moving apart. This is fundamentally anti-Newtonian, unless there is a force we are unaware of. For lack of better guess at this time, we have labeled it "dark energy". We do not understand it, so are not near being able to harness it for conversion into work.
      • Feb 5 2014: Very interesting. So the answer may lie in the mystery of this dark energy. I believe that physicists will slowly begin to unveil these secrets.
  • Feb 2 2014: One of the best known ways of storing electricity from when it can be created, to when it is needed, is pumping water up hill, converting electricity to potential energy, then using gravity to allow the water to move back down, converting potential back into electricity.

    This is used for storage of wind and solar to be used when the wind is not blowing and the sun is not shining.

    Here in AZ, our nuke plant cannot produce all the electricity we need during peak summer usage. At night, we use the nuke electricity to pump water up hill behind a damn. The next afternoon, when we need surge electricity to meet demand, we use gravity to convert the potential energy in the water back into electricity.
  • Feb 2 2014: Gravity does not put objects into motion. The motions is remnants of kinetic energy left over from the big bang, or the last super-nova to explode the matter into motion. Gravity simply bends space/time (or something like that) such that the object thinks it is moving in a straight line through space, but that straight line is actually through curved space. At least, that was Einstein's best guess, and testing has held up.


    Energy is not harnessed via potential difference alone. It is harnessed via the resolution of potential difference.

    Solar knocks electrons through a semi-conductor, creating potential difference in charge. It is not until we allow the electrons to flow back, resolving the potential difference, that we can harness the energy to do work.

    Gasoline exploding in an engine creates a pressure difference between the top and bottom of the piston, but only by allowing the piston to move down, resolving the potential difference, can we harness that energy.

    To harness gravity, it is not sufficient that there be a potential difference, but you have to resolve that potential difference. That is, it is not enough that two objects be at a distance while pulling on each other. To harness that potential difference, we have to allow it to be resolved. That means the two objects moving closer together.

    We do this with hydro-electric power. We allow water to move closer toward the center of the earth, capturing the energy.

    The first internal combustion engine exploded a heavy weight up, then captured the energy as the weight fell.

    In the case of large objects, like stars, planets, moons, there is massive potential energy there, but I do not think we want to crash the moon into the earth to convert that potential energy into usable work.
    • Feb 3 2014: That is what I'm trying to get clear. So all the "heavenly bodies" in the universe, are in motion because of the kinetic energy that has remained since the big bang? Do you have any sources on this exact statement? Not that I don't believe you, just want to read more on this subject. Why is eveything in the universe on the move, in motion? What makes it all move in the way it does? You say that gravity bends space/time, isn't gravity itself space/time?
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        Feb 3 2014: What moves you as an individual?
        What happens when motion stops?
        Gravity grips life/energy that feeds the planet. When things get moved to outer space, then life/energy is lost. Things burn up when entering Earth atmosphere, protecting the Earth from outside influence.
        Current practices of moving energy to outer space, affecting ozone, and drilling deep downward, seem to be direct attacks against Earth.
        Wonder if possible Earth could tighten up and increase gravitational pull toward its core?
      • Feb 3 2014: Pretty much any article on the Big Bang should be able to provide an overview.

        The hard truth is that we are not really sure what happened. Why more matter than anti-matter? Why so little strange matter (more than 3 quarks)? We have guesses, like the universe expanded than normally possible.

        We started running calculations on the mass of visible matter in galaxies and comparing to their shape, and found not enough mass to bend the paths of stars that much, so we guessed there must be dark matter.

        For the better part of a century, we assumed the expansion of the universe was slowing down, then we were able to test the rate at which it is slowing down and were shocked to find out it is really speeding up. Poof, the idea of dark energy.


        Bottom line is that we do use gravity for energy. Hydro-electric is gravity energy.
  • Jan 29 2014: Some time back I had come across the Invention wherein with the use of Gravity the power lamps are made so that when weight comes down due to gravitational force and while coming down it generates the power using cog wheels and which in turn spins the wheel making electricity generation. More Information can be found using following url.
    http://science.howstuffworks.com/environmental/green-tech/sustainable/gravity-powered-lamp1.htm
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    Jan 29 2014: If I try to imagine amount of energy "behind" all gravity fields, around observable matter, it would be at least 1.29140163 × 10^58 Jouls. That is assuming we have correctly estimated minimum mass of the matter in observable universe. Source behind that force called gravity is energy, also called as matter. :) People have already mastered to harness that energy to some extent, by splitting atoms. Although, its just splitting, not 100% conversion to energy, only a fraction is converted.

    But if you are asking about using interactions of matter through gravity as energy, then it has been in use in one form or the other since the time of first watermills.
  • Jan 29 2014: Energy can be harnessed from gravity and is. I designed an engine that uses gravity on the downstoke and a light gas like oxygen on the upstroke. The ultimate no cost, scalable, perpetual energy.
    • Feb 5 2014: That sounds very fascinating. Could you send my a link to your website or something?
      • Feb 5 2014: Tom this was many years ago before websites but the idea simply combined two phenomena's: The first one was how they raise sunken ships by filling compartments with a gas or compressed air which generates energy on the way up, the down stroke generates more energy as the object heavier than the liquid around it sinks to the bottom because of gravity. The combination becomes a perpetual engine generating energy going up and down. I figured it would be a perfect peace time use of all those missile silos we dug in the 60's but a giant generator could be made in any body of water, a lake or ocean for instance. There is already a huge natural generator going on with the weather where water condenses and forms rain clouds which carry water to the top of a mountain and releases it in the form of rain and snow. It then melts and runs down the mountain (gravity) and back into the ocean or lake then continues the cycle all over again. There is energy all around us, for us to have to "pay" for energy is quite insane! That's like paying for water when you are on a boat??
        We use gas to create combustion when we would be far better off perpetually recycling it in it's natural state without changing it back into carbon.