1. hi,

i was watching a documentary on discovery about the moon, how the tides are affected by the moon and a thought came to mind

the gravitational pull on the ocean causes the tides to occur, and these tides /could/ be used to drive a generator

now i know you cannot get energy for free, and so im trying to figure out, where is this energy coming from?

2.

3. Originally Posted by maUru
now i know you cannot get energy for free, and so im trying to figure out, where is this energy coming from?
You said it yourself. It comes from the gravitational pull of the moon.

4. so the gravitational between the moon/earth is weakening gradually?

i thought gravity was dependant on mass.

5. Imagine gravity is like a rope connecting the Earth and the moon. The moon is spinning around the Earth and held in place by this rope. If you extract energy from this set-up, you are not getting it from the rope. You are getting it from the spin. So the spin slows, but the rope is the same as always.

6. As a consequence of the energy input into the tides on the Earth the moon is slowly moving outwards, away from the Earth, to a lower energy orbit. The net energy of the system remains the same.
When the moon was formed, following a collision with the proto-Earth by a Mars sized planet, it was only 15,000 or 20,000 miles away from the surface and the tides raised by it were huge - possibly as much as a kilometre. Over time it drifted away to its present position of around 250,000 miles.
Associated with this drift and the Earth tides is a gradual slowing of the Earth's rotation. [At formation the Earth turned every six(?) hours.] Eventually the Earth will be tidally locked with the moon, so that the same face will always be turned towards it.

7. Originally Posted by Ophiolite
As a consequence of the energy input into the tides on the Earth the moon is slowly moving outwards, away from the Earth, to a lower energy orbit. The net energy of the system remains the same.
When the moon was formed, following a collision with the proto-Earth by a Mars sized planet, it was only 15,000 or 20,000 miles away from the surface and the tides raised by it were huge - possibly as much as a kilometre. Over time it drifted away to its present position of around 250,000 miles.
Associated with this drift and the Earth tides is a gradual slowing of the Earth's rotation. [At formation the Earth turned every six(?) hours.] Eventually the Earth will be tidally locked with the moon, so that the same face will always be turned towards it.
Wow, when is the Earth going to stop rotating ?

MaUru:

There are already several systems designed to harness the energy from tides and waves.

8. [quote="oracle"]
Originally Posted by Ophiolite
Wow, when is the Earth going to stop rotating ?
We should ask the oracle that question. Hey, that is you.

As long as there is an earth, it will rotate.

9. id say it wont stop, once the moon get enough away it will leave orbit

10. :? the earth without a moon? i would say there is a big chance the moon will form a ring of debree around the earth..

The moon will get back to earth when the rotational point of the earth has less effect on the moon and just the attracting effect will work.

This way the moon will come closer to earth and will be nuked, so a ring of debree will form..

11. Originally Posted by Zwolver
:? the earth without a moon? i would say there is a big chance the moon will form a ring of debree around the earth..

The moon will get back to earth when the rotational point of the earth has less effect on the moon and just the attracting effect will work.

This way the moon will come closer to earth and will be nuked, so a ring of debree will form..
I missed that episode of Star Trek.

12. Originally Posted by Zwolver
:? the earth without a moon? i would say there is a big chance the moon will form a ring of debree around the earth..

The moon will get back to earth when the rotational point of the earth has less effect on the moon and just the attracting effect will work.

This way the moon will come closer to earth and will be nuked, so a ring of debree will form..

But...we are talking about the rotation of the earth around its own axis arn't we ? How does that influence the position of the moon ?

13. Originally Posted by Ophiolite
As a consequence of the energy input into the tides on the Earth the moon is slowly moving outwards, away from the Earth, to a lower energy orbit. The net energy of the system remains the same.
When the moon was formed, following a collision with the proto-Earth by a Mars sized planet, it was only 15,000 or 20,000 miles away from the surface and the tides raised by it were huge - possibly as much as a kilometre. Over time it drifted away to its present position of around 250,000 miles.
Associated with this drift and the Earth tides is a gradual slowing of the Earth's rotation. [At formation the Earth turned every six(?) hours.] Eventually the Earth will be tidally locked with the moon, so that the same face will always be turned towards it.
Last time i checked the closer two bodies are the smaller the amount of gravitational potential energy Doesnt that mean the moon would drift toward the earth?

14. earth loses rotatinal energy, something must gain this energy, our companion moon is the answer. so it goes further away

15. I am getting very dizzy :?

16. earth have rotational energy, everything rotating does
when earth slows down by tidal force it loses energy, that have to go somehwere, that thats where moon come into the picture. it gets that energy in form of potensial energy. if this didnt happen energy would be destroyed

17. Originally Posted by Ophiolite
As a consequence of the energy input into the tides on the Earth the moon is slowly moving outwards, away from the Earth, to a lower energy orbit.
I'm pretty sure you've got this backwards; the earth's rotation slowly accelerates the moon, which causes its orbital radius to increase and slows the earth's rotation.

The earth rotates in the same direction that the moon orbits, which causes the tidal "bulge" of the ocean to constantly move ahead of where it should be based on the moon's position. The gravity of the moon tends to pull the tidal bulge backwards, which slows the earth's rotation. This also accelerates the moon forward in its orbit slightly, which causes it to increase its distance from the earth.

18. :? isn't it in balance somehow?

19. if it were accelerated it would acctualy go out of orbit and not increase it, becuase the speed at futher distance is even slower, so the further it goes the less speed it need and thereofr allways have escape velocity- unless it becomes a eleptic orbit

20. Originally Posted by Zelos
if it were accelerated it would acctualy go out of orbit and not increase it, becuase the speed at futher distance is even slower, so the further it goes the less speed it need and thereofr allways have escape velocity- unless it becomes a eleptic orbit
It moves slower in its orbit once it reaches a new stable orbit, but some of the energy that's transfered from the earth's rotation to the moon goes toward lifting it away from the earth.

21. nope, once reached escape velocity it keeps escape velocity

22. If earth spins slower and slower, that means gravity will increase

If I hold a wet basketball in my hands and spin it, water drops shoot outwards from its 'equator'. If I spin it slower, the water barely moves outwards and drops onto the floor close to the ball.

23. no, gravity is the same, its just the amount of force we feel change slightly

24. :? can you really feel it... it'll be a change of 0,0000000000001% per lifetime or something.

good senses you have :P

25. lets make some calculations
V=D/T
D=2pi*r
T=24*60²
r=6356620m
g=9,80665
acceleration outward due to spinning around the exis at the equator = 0,0336
g at equator = 9,80665-0,0336=9,773
so yeah it is noticble

26. Originally Posted by oracle
If earth spins slower and slower, that means gravity will increase

If I hold a wet basketball in my hands and spin it, water drops shoot outwards from its 'equator'. If I spin it slower, the water barely moves outwards and drops onto the floor close to the ball.

But...I don't get it. To me, when oceans rise because of the moon attraction, that means the moon attracts us as well. Thus, we temporarily weigh a little less. If the moon is gone, and the earth spins slower....that means we'll weigh even less

27. no

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