
#19
Jan1810, 10:06 PM

P: 6





#20
Jan1810, 10:11 PM

P: 15,325





#21
Jan1810, 10:19 PM

P: 2,041

Energy is transferred, not destroyed. So, if it takes Energy to keep the moon in orbit, where is this energy going? 



#22
Jan1810, 10:38 PM

P: 6





#23
Jan1810, 11:07 PM

P: 2,041

Some of that energy is dissipated as heat because there is friction between the oceans and the Earth. Some of that energy is transferred to the moon, which makes it orbit larger as time goes on. (As I mentioned in a previous post)
But there are no frictional forces in the Earth/moon system (to first approximation anyways), so why would energy be dissipating as heat? 



#24
Jan1810, 11:44 PM

P: 6





#25
Jan1910, 12:09 AM

P: 2,041

Were we talking about the wave/Moon system? I thought we were talking about keeping the Moon in it's orbit.
The energy from the wave/Moon system comes from the rotation of the Earth (Hence, why the Earth's rotation is slowing down). It's the rotational kinetic energy. 



#26
Jan1910, 01:20 AM

Mentor
P: 14,433

Caveat: The Moon is slowly receding from the Earth due to tidal interactions (very slowly; 3.8 cm/yr currently) and the EarthMoon system is losing a *tiny* bit of energy in the form of gravity waves. These changes are extremely tiny in comparison to the Moon's orbital energy. Ignoring those tiny effects, there is *no* change in energy as the Moon orbits the Earth. I'll start with a circular orbit. The gravitational potential energy is obviously constant in a circular orbit. While the velocity vector is constantly changing direction in a circular orbit, the magnitude of the velocity vector does not change. As kinetic energy is 1/2mv^{2}, kinetic energy is also constant in a circular orbit. For a noncircular orbit, gravitational and kinetic energy do change over the course of an orbit, but the sum of gravitational and kinetic energy remains constant. There is no change in energy as two objects orbit one another. 



#27
Jan1910, 03:38 AM

P: 51




#28
Jan1910, 04:39 AM

P: 1

i dont know




#29
Jan2310, 10:11 PM

P: 3

Classical Physics relates to the observable universe. We are aware of gravity's grip and we observe its interaction with our universe. However, we do not know how gravity operates. While we can accurately define gravity's observable effects, we do not understand the nature of gravity.
Think about it. This is a fundamental force that works throughout the universe. Yet, we are unable to describe what or how this is being done. It may be that we are unable to understand gravity. Since we spend our entire life in its grasp, perhaps we are restricted from seeing it for what it is. I do not care to believe this. Gravity may be a separate form of energy or it may be a part of the energy we already know. The only thing we truly must face is that we do not know what it is. Only by accepting that fact will we begin to believe there are other ideas of what gravity is and what it can do. Gravity is the only force that we are unable to shield, direct, create, or destroy (use up as in transfer). Gravity is a perpetual force that can be found everywhere and if we could understand anything about it, we would never need another source of energy. Wow, don’t believe this? OK, consider this, if we could diminish or increase gravity’s effects in a prescribed area, we could create an unequal gravity field. If we could place one side of a balanced flywheel in the field, the flywheel would become unbalance and would begin to turn. One side of the flywheel is actually falling through the heavier side of the gravity field. While the field remains stable, the flywheel will continue to turn as its edge enters the unequaled gravity field. This means that a knowledge of gravity could, at the least, provide us with a constant, unrelenting source of energy anywhere on this planet. And that is only if we knew how to increase or decrease gravity in one small area. Isn’t this enough encouragement for us to put everything we can into discovering what gravity really is and not just what it does? 



#30
Jan2410, 01:07 AM

Sci Advisor
PF Gold
P: 9,174

The moon moves when an object slingshots around it. Gravity is not a force, it is the curvature of space due to matter.




#31
Jan2410, 12:45 PM

P: 446

How about this. We have two steel balls attached to each other with a wire. They are spinning around each other in empty space. No gravity involved. The force that causes the acceleration comes from the tension in the wire. The force of the wire of ball1 is equal and opposite the force on ball2. There is no net force.
If you believe the acceleration is doing work then after some time we should see some effect of that work. But nothing changes the temperatures remain the same. The velocities remain the same. So where is the energy going? Work = force (dot product) distance. In this case force and distance are perpendicular so the (dot product) is zero. 



#32
Jan2410, 06:12 PM

P: 3

This is a great demonstration of the effects of gravity; however, it does not explain how gravity does what it does. As to the question of whether gravity is a force, step off the fifth floor of a building at sea level on planet Earth and tell me if there is not a force at play. For that matter, help a buddy move his stuff into an upstairs apartment and tell me what you are fighting as you climb the stairs with his futon. The real answer is not a definition of what gravity does, but an explanation of how gravity does it. Conquering gravity would liberate the human race. 



#33
Jan2410, 06:19 PM

P: 3

Ok, there is no gravity (perceptible gravity) at play, so why is this part of the discussion? It is a good thought experiment, but the true energy in this example was applied at the beginning when the balls were originally flung in the “orbit” you have created. They will eventually slow down as effects from other objects play on them, but, aside from the centrifugal force that would separate the two if the wire were cut, there appears to be no other forces at play. What am I missing? 



#34
Jan2410, 06:23 PM

P: 15,325





#35
Jan2410, 08:22 PM

P: 446




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