Speed of Gravity

[asallen]

What is the speed of gravity? i.e. If the moons gravity was turned off, how long would it be before the effects were felt on Earth?

[Gigadave]

If I remember my science lessons from school, then the terminal velocity anything can fall at is 120m/sec. The moon is roughly 400,000km away so you do the math! Cos it's too early for me to get my head round this! And what would the effects be? Except for the tides...

[rekstout]

Gravity is a fundamental property of matter and as such does not have a "speed" like light does. If the moons gravitational effect was stopped the the effect would be instantaneous - it may take a few seconds before things like tidal movements and earth tremors (if any) were felt as the oceans and tectonic plates adjust to the new gravitational forces upon them

Terminal velocity is not dependant upon acceleration due to gravity but due to the fluid in which a body is moving and the nature (shape, coefficient of friction etc) of the body. For example, there is no terminal velocity in a vacuum, an object being acted upon by a constant force will constantly accelerate.

[Obo]

Gravilty doesn't have a speed it has an acceleration which I seem to remember is 9.8metres per second squared so when you drop and object it accelerates at that rate (regardless of the weight of the objct as shown by Newton's laws of motion)

[Obo]

Further to my previous answer, Gravity is a force that does not itself have a speed, but a direction and a magnitude (being a vector) the magnitude of this force controls the acceleration of objects it acts upon and in the case of the Earth this acceleration as I stated is 9.8 metres per second squared. With regard to terminal velocity this is controlled by a numbe of factors, assuming you knew the density of the moon (avg) it's diameter, and the density and viscosity of the space inbetween the Moon and the Earth you could use the following link http://www.processassociates.com/process/separate/
termvel.htm to work out the termnal velocity the moon would accelerate to and there for approximately how long it would take to crash into the Earth

[asallen]

Thanks for your answers but i am not sure if I have worded my question correctly. Let me re-word the question. Imagine a large mass were suddenly to appear in space, lets say one million miles away. how long would it be before the gravitational effects be felt on earth? If the sun were to disappear and suddenly reappear it's light would take about 8 minutes to get here. But what about its gravitational field? If the answer is instantly, then the answer to my question would be much faster than light. To take this further, If we then found a way to modulate gravity waves, (do they exist?)(dont answer that!) then instant communication could be possible over vast distances. It may be that I have been watching too much Star Trek or perhaps I have drunk too much.Where's my beer?

[rekstout]

I understand where you are going with this as I have seen the recent press article on the alleged experiments where g (acceleration due to gravity) was varied by 5% somehow - even it it were true, the variance would not be perceivable over a sufficient enough distance to make it a viable means of telecommunication. It would be rather like seeing the difference in light between a 100 watt bulb and a 95 watt bulb from a 100 miles away.

[simon_says]

9.81m/s/s

[Hamish]

There's a lot of debate about at the moment about gravitaional waves, ie the mode of transmiaation of gravity described by a quantum method. The maximum speed would therefore be the speed of light (sorry no fast long distance calls!) Hamish

[DaveRH]

Some experiments were concluded recently which did support the theory that the effect of gravity does in fact travel at the speed of light...

[Haitch]

A scientist recently got caught out as having faked a number of experiments (The Bearings Bank of the science world). I'm not sure but I've got a feeling that he may have been the one carrying out these experiments.