Sir Newton will tell you that gravity is the attractive force that exists between any two masses. Prof. Einstein corrected (or expanded) that idea, and today gravity is defined by the concept of relativity. It is still the attractive force between two masses, but it is also so much more.....

Gravity is often one of the more annoying features of our universe and this is rarely more true than when trying to explain it.

At best I can only direct your friend to look into M theory, gravitons, branes, loop quantum gravity and so forth. It shouldn't take more than a decade to do this thouroughly, but I recommend frequent alternnating breaks for aspirin and the ethenol-bearing beverage of his choice.

My personal suspicion is that gravity is merely a construct to keep all the dust down.

Gravity is what makes what goes up come back down.

The force of gravity becomes greater as you add more material to the 'main' object.

Add enough material, and the combined density of the materials will create enough heat and pressure to burn in a nuclear fashion.

Add even MORE material... a LOT more... and the space between the nucleus and the really heavy, but infinitely small electrons will decrease to the point where even photons of light will not reflect.

....add even MORE! and you have a universe that collapses with such force that it explodes and starts all over again.

It's cool stuff..

...of course all of this is my own dumbed down speculation. . no facts were harmed in the generation of this response.

...so i guess you could say I'm so full of it that I should carry a fire extinguisher.

Gravity is an illusion. It does not exist. The phenomenon we call gravity happens because everything in the universe sucks.

Yeahhhh, right!

Gravity...? Then why have we not observed tides in our atmosphere? ...or any atmosphere?

Bobguz

Actually, there are tides in the atmosphere, but we don't notice them because we are at the bottom of this ocean of air.

Likewise, critters that live on the bottom of the sea don't notice those tides unless they are near a coastline.

You are correct for atmosphere.

But on the other hand there are tides for the ground (earth surface). We are on the earth surface. Still we do not feel the tide.

Pardon, but, unlike fish, we would perceive tides in the atmosphere as a diurnal change in barometric pressure. That don't happen. Also a tidal change in the altitude of our atmosphere would quickly slow anything in low (??) orbit. I never heard of that either.

Bobguz

"If we all worked on the assumption that what is accepted as true is really true, there would be little hope of advance." -- Orville Wright

You apparently have never observed the output of a graphing barometer! I'm not at home right now, so I don't have any available to post, but when I get home in a couple of days I'll see if I can do that.

There IS a diurnal change in barometric pressure, and just like in the oceans, one of the highs is regularly higher than the other. The tides in the atmosphere tend to be masked by changes due to weather, but it does not take a meteorologist, just a careful observer, to see them.

All satellites have to be high enough to be above virtually all of the atmosphere, or they would (and eventually will, unless they are periodically boosted back up) be slowed by the atmosphere, tide or not.

Dick

Lets consider the gravitational attraction between a pretty girl and a boy.

If a 50 kg (110 lb) pretty girl sat 0.5 m (19.7 in) from a boy who was 75 kg (165 lb), what would be the gravitational attraction between them?

According to the Universal gravity equation we get:

F = GMm/R² = (6.67*10^-11 N-m²/kg²)(50 kg)(75 kg)/(0.5 m)(0.5 m) = 10^-6 N or one-millionth of a Newton

That is a very small gravitational attraction, but it can be measured on a sensitive instrument.

At least, thats what I would tell the girl.

Most engineers That are not in electronics at Component level are quite content to live in Newtons Universe.

Example calculation frm http://www.school-for-champions.com/science/gravity_universal_equation.htm where you should send your friend.

milo

But if girl is sitting on the laps of the boy, R becomes very small. Please let us know what will be the gravitational force.

Also if girl is of 75 Kg and a boy 50 kg. what are the effects in above case?

In the case of a 75 kg girl and 50 kg boy, the math formulas give the same answer, but the "sensitive instrument" usually fails to respond to any attraction.

milo

So you want to say a 500kg girl will be more attractive?

The numbers say that. I have a somewhat different answer...

milo

Science has yet found out how it works. But no body has yet understood why it is so.

So no answer to your question "Where does that....."

Ask Jorrie, he is the CE4 expert on the subject of relativity.

Get an ebook copy of "Relativity 4 Engineers."

Good post, Vermin! There is still a debate going on re "gravity waves" and Gravitons.

If a Graviton is essentially massless, like a photon, and if even photons can't escape from a massive body, such as a black hole, why do we think that black holes radiate gravitons? If matter (atoms) in a neutron star are basically collapsed atoms where the electrons and protons have been crushed together to produce neutrons, then what form of matter exists in a black hole (Singularity?) Because the black hole does have "gravity", matter / mass must still exist in the black hole.

This is where Relativity and Quantum Physics get in a fight and don't speak to each other for several days.

QM has been able to explain all the forces by the exchange of virtual particles... Except one - they just can't seem to find that "Damn elusive Graviton!"

Great post. Consise, percise, and to the point.

Thank you,

Orpheuse

You asked:

"What is gravity?" : It's the attractive force between masses or energies due to the curvature of the "space-time continuity" which is caused by the presence of these masses or energies (according to the General Relativity of Einstein)

"Where does that pulling force come from?" It comes from masses or energies (as I've already told you)

"What is it's purpose?" : What is the purpose of everything else???... Its existence is not more mysterious than the existence of everything else...

"Actually why it pulls & not repells?" : I could ask: why electric or magnetic force pulls or repells and doesn't, always, pull??? ... It's just the nature of the gravity as there are not positive and negative masses in order to have, correspondingly, attraction or repulsion (due to gravity)... It's not like i.e. electric force which is caused by positive or negative charges...

Although it is important to note that anti-matter acts the same way a regular matter in a gravitational field.

To me gravity is a distortion of what I call the point of equilibrium. Space is a medium that is in equilibrium, and if you introduce a mass into it, the point of equilibrium is moved. So what does the point of equilibrium mean? To use an analogy, if you jack up the back of your car and put a motor on each rear wheel, each running in an opposite direction to each other, then take a meter reading of the loads, they should be in equilibrium, the load divided to overcome friction. Now start the engine and through the clutch pass some load to the rear end, this being the equivalent of mass in space, a separate energy introduced into a environment in a state of equilibrium, then one will resist and the other will accept the input, the result an increase of load on one motor and a decrease on the other, gravity being the increase and the other force part of the equilibrium equation not giving any reading on the meter at all? The end result being you can only read one force the other being undetectable? Like I said this is just an analogy, not a theory.