I was thinking about this today.....

Let's say that I'm holding a rock in my hand and I drop it. When I drop the rock, not only will it fall to the ground, but the earth will, in fact, move up to meet it. Look at it this way: If I was holding a rock in my hand, and this rock had a mass that was equal to the earth's mass, then it would have gravity equal to that of the earth. So when I dropped it, because of gravity it would only fall halfway; the earth would move to meet it.

So when I drop this small rock in my hand, the earth is going to move (an unmeasurable amount) up to meet it. Interesting.

Gravity...

Here's a better one. When you walk do you move across the earth or do you push the earth back behind you?

of course we are talking about fairly negligible amounts of force here... it is only when we have high measures of energy acting against gravity that we actually care (such as for escape velocities of rockets)

Be that as it may, Rogue, it still makes me feel smart when I talk about it

does that mean u have a new screen name then duddy?

See that cat over there??

It came out of that bag he's holding!!

that was nice fer... good pun

Ok, everyone in australia brace yourselves, I'm gonna jump onto my bed

No, I just post under Darth Dud occassionally. A product of my boredom, nothing else.

are u now disparaging my masculinity with your siggy then?

this is not ur week for tact

You people are never going to let me forget, are you?

Sorry to disappoint, but you haven not taken mass into account. The poor rock does not have enough mass to even make the earth beneath your feet twitch.

It has... I lack the time to look up the formulae proving so, but ANY object with mass attracted to the earth, will attract the earth to itself as well.

Every object in the universe exerts a gravational force on the others, it might be infinitessimal but it's there

Since the gravitational force is experienced by all matter in the universe, from the largest galaxies down to the smallest particles, it is often called universal gravitation. Sir Isaac Newton was the first to fully recognize that the force holding any object to the earth is the same as the force holding the moon, the planets, and other heavenly bodies in their orbits. According to Newton's law of universal gravitation, the force between any two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The constant of proportionality in this law is known as the gravitational constant; it is usually represented by the symbol G and has the value 6.670 × 10−11 N-m2/kg2 in the meter-kilogram-second (mks) system of units. Very accurate early measurements of the value of G were made by Henry Cavendish.

Newton's theory of gravitation was long able to explain all observable gravitational phenomena, from the falling of objects on the earth to the motions of the planets. However, as centuries passed, very slight discrepancies were observed between the predictions of Newtonian theory and actual events, most notably in the motions of the planet Mercury. The general theory of relativity proposed in 1916 by Albert Einstein explained these differences and provided a geometric explanation for gravitational phenomena, holding that matter causes a curvature of the space-time framework in its immediate neighborhood.

Tantalizing evidence for the existence of gravity waves, which are predicted by Einstein's general theory of relativity and would be analogous to electromagnetic waves, comes from astronomical observations of a binary pulsar designated 1913 + 16. The rate at which the two neutron stars in the binary rotate around each other is changing in a manner that is consistent with the emission of gravity waves. A hypothetical particle, given the name graviton, has been suggested as the mediator of the gravitational force; it is analogous to the photon, the particle embodying the quantum properties of electromagnetic waves. The search for gravity waves continues with plans to build large interferometers that would be sensitive enough to detect the faint waves directly.

Or so I'm told

Let's do a practical example. I drop a stone to the earth...

Let's say the stone is a sizable one. 1 KG (2 pounds) in weight. From a height of 1 meter.
Relevant formulae:
F(g)=m*g
F=m*a -> a=F/m : 2nd law of Newton

Now, since earth attracts the stone, earth puts a "pull", a force onto the stone. The same pull the stone puts onto the earth. This means the gravitational constant of the earth can be used for F:
F(g)=m*g
g is a constant, depends a bit where on earth you are. Varies from 9.8 to 9.91 if I'm not misstaken... For me it is 9.81 m/(s*s)
m=1KG... This would result in:
F(g)=9.81

So back to the earlier formula.
a=F/m
9.81=m(earth)*a

Earth's mass is 5,976*10E24 KG

Earth would accellerate with 1,641*10E-24 m/s*s towards the stone. That is 0.0000000000000000000000001641 m/s*s, a small figure indeed.

and even if u took every human to one side of the planet and made them jump, that figure would only move up a few decimal places...

Remember as kids, we (I) thought that if you got all the children in China to jump all at once, the entire world would shift..?

NOw, say we did that... Would the earth move east (up, towards the children), or west (due to the force of resulting impact)...

But hey, I'm about to give up on my Physics classes, so I'm not much of an expert...

It would move west when they jumped, then east an equal amount due to the gravitation... The net accelleration would be 0. The net movement also be 0.

stares in awe at Aeternus's smartness.