Gravity: The Endless Energy Source?

In summary, the Earth's gravitational field stores energy that is released when a mass is lifted and falls back down. This energy is not infinite and is not needed to keep an object at rest on the Earth's surface. The concept of "forever" and infinity must be carefully considered in physics. The bending of light by the Earth's gravity can also be explained using the theory of general relativity. The understanding of potential energy can help make classical gravity more understandable.
  • #1
cragar
2,552
3
When I lift a rock up and let it go it always falls back down in the presence of the Earth's G field . So where is this infinite energy supply coming from . why does it always pull it back , assuming were not talking about escape velocity. Or am I viewing this incorrectly.
 
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  • #2
The energy came from you and allowed you to lift the rock. I don't believe your supply is infinite. :)
This energy was stored in the gravitational field, and released when you let the rock fall.
 
  • #3
i guess what i am asking is , let's take a rock sitting on the ground will the G field of Earth always keeping it there forever , where does the energy come from to distort space-time and make things accelerate towards it and keep it there forever , it seems like gravitational energy is infinite .
 
  • #4
Let's separate out a couple of things here.
First, as far as energy in the sense of "doing work" is concerned, the Earth is doing no work and thus needs no energy, to keep the mass at rest on its surface. So, keeping it there forever is not an infinite amount of energy.
This brings us on to "for ever", and infinity. These are always terms which need to be treated carefully in physics. (There have been a couple of threads on this here recently).
The Earth has mass, but not an infinite amount, and this mass distorts space-time, but not by an infinite amount. So I don't see where the idea of an infinite amount of energy comes from. If you ask whether this lasts "for ever", that is another matter, and you are asking if the universe lasts for ever. Even if it does, it does not imply that the Earth is doing, or going to do, an infinite amount of work; and therefore doesn't need (or posses) an infinite amount of energy
 
  • #5
Consider a mass sitting on a spring. Is the spring constantly exerting energy to hold the mass up?
 
  • #6
right, you need to get clear in your mind what the differences are between 'force,' 'energy,' and 'work.'
 
  • #7
ok let's take a continuous light ray moving past Earth as it comes by Earth it bends and changes it course of direction , what allows Earth to bend this light , let's say the light beam is infinitely long .
I kind of get what you are saying about the mass and spring
 
  • #9
what allows Earth to bend this light

Answer: same as your post #1. (you can use rocks, cannon balls... satellites all the same. Light or photons (electromagnetic radiation) is definitely more mysterious and stumped scientists until Einstein explained it.

You can attempt to get insights into such very subtle and in some respects difficult aspects of gravity by repeating thousands of years of "intuitive" studies by thouands of people studying thousands of examples...OR...you can try working from the theory which results from all those efforts, see if it makes snese, then try applying that theory to problems which interest you. For most of of us mere mortals (not Einstein's) the second path is a LOT faster and more instructive.

If you understand potential energy, energy of position, calssical (Newtonian) gravity is more understandable:

Gravitational energy is the potential energy associated with gravitational force. If an object falls from one point to another inside a gravitational field, the force of gravity will do positive work on the object and the gravitational potential energy will decrease by the same amount.

http://en.wikipedia.org/wiki/Gravitational_potential_energy#Gravitational_potential_energy
 
  • #10
ok thanks for the replies i think i understand better , thanks for the link on GR dalespam
 

1. What is gravity and how does it work?

Gravity is a fundamental force of nature that causes objects with mass to be attracted to each other. It works by exerting a force between objects based on their mass and distance from each other.

2. Is gravity really an endless energy source?

While gravity is an abundant force in the universe, it is not technically an endless energy source. It is a conservative force, meaning that it cannot create or destroy energy, but it can convert potential energy into other forms.

3. How can we harness gravity as an energy source?

One way to harness gravity as an energy source is through hydropower, where the gravitational pull of water is used to turn turbines and generate electricity. Gravity can also be harnessed through tidal energy, where the gravitational pull of the moon on Earth's oceans is used to generate electricity.

4. Can gravity be used to power space travel?

Gravity can be used in space travel through the use of gravitational slingshots, where a spacecraft uses the gravitational pull of a planet to gain momentum and speed. However, gravity cannot be used as a direct source of propulsion.

5. Are there any potential negative effects of using gravity as an energy source?

While harnessing gravity as an energy source can have many benefits, there are also potential negative effects to consider. For example, large scale hydropower projects can have significant impacts on local ecosystems and disrupt natural water flow. It is important to carefully consider and mitigate these potential effects when utilizing gravity as an energy source.

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