Having read the question
it seems as if it was tailored for me alone. My best friend and I often have a drunken argument about gravity, which is always impressive and leads to us fending off the ladies in their droves as you can imagine.

Whenever we get together in an alcohol fueled environment, it starts. "We only have gravity because earth is spinning. If earth stopped spinning, we'd all float away." The proof of this, astoundingly, is "If you spin a bucket of water around your head the water stays in the bucket." I, like a large section of society I imagine, am not quite sure of the facts and figures when it comes to astrophysics, so am unable to offer a completely sound argument to dissuade him from his beliefs, and "For fucks sake, gravity is just a thing" doesn't seem to cut it.

He has a new one, though. In what seems to me like an effort just to wind me up, he recently let it slip that he believes the effect the moon has on the tides here on earth is "A load of shite" and tides are caused by hot water and cold water mixing. Trying to explain that this is what causes currents but not tides, which are caused by the moon's gravitational pull (which was a stretch after 6 pints, 2 vodkas and a stiffy) was met with the response "Does it fuck. How can it? It's fucking miles away!"

Explaining that all of earths scientists would have to have not thought of his hot/cold theory did no good.

I text him about it the following day and he denied he ever said anything. There are clumps of my hair on the pub floor to prove otherwise.
( baw__bag contains traces of nuts on, Thu 18 Mar 2010, 17:41, 9 replies)

Force=mass x acceleration
Where Acceleration = rate of change of speed

Is one of Newton's laws. A more accurate way of writing it would be to say that force is rate of change of momentum, and momentum is the mass of an object multiplied by its velocity.

The key word here is velocity. "Speed" says nothing about the direction that something is moving in: in mathmatical jargon it's called a 'scalar' - a value that only has one property. Velocity is what's known as a 'vector' because it doesn't just depend on how fast something is moving, it depends on the direction it is moving in too.

It follows that if something is moving in one direction and a given speed and is shifted so that it is moving in a different direction at a given speed its momentum will have changed - exerting a force on the object.

This is a slightly long-winded way of saying that any object moving in a circle is constantly changing momentum and as such has a force constantly acting on it. In this case, centrifugal force. This is what keeps the water in the bucket.


(P.S. Please, please don't tell me that centrifugal force doesn't exist, and it's all centripetal. You teachers may have told you this, but they lied.)
( MatJ LOOK, Thu 18 Mar 2010, 18:22, closed)

My explanation was far more technical.
"The water's trying to fly through the bottom of the bucket and away from your shoulder, not being attracted to your shoulder which is the what's spinning. If your shoulder was the centre of the earth and we were water, we'd all try to fly away from the ground, not stick to it." Or words to that effect, with a few hiccups in between. He just looked at me funny.
( baw__bag contains traces of nuts on, Fri 19 Mar 2010, 20:44, closed)

hmm
centrifugal force is just a shorthand way of saying the acceleration (f=ma) is due to things spinning about in a rotational kind of manner. There's no such thing as a force specific to spinny things as such.

I hate grammar nazis, and now I'm a inertia nazi.

AN inertia nazi. Damn.
(inflateable, Mon 22 Mar 2010, 21:29, closed)

Explain to him that for the water to stay in the bucket it needs a force acting radially inwards
If the earth was spinnign and we didn't have gravity we'd all get thrown off
( greedyostrich Cheese is evil! Cheddar is VOODOO!, Thu 18 Mar 2010, 19:40, closed)

Also ask about the poles
since you'd only be spinning very slowly on the spot when standing there.

Or is the reason Scot of the Antarctic didn't come back because he stood on the South Pole and, with insufficient gravity, floated away into space?
(Honourable Member is upstanding, Fri 19 Mar 2010, 8:23, closed)

The poles!
That's it! I never thought of that, I've tried for ages to find something simple enough to refute his theory that is A: understandable and B: easy to remember when drunk :D
( baw__bag contains traces of nuts on, Fri 19 Mar 2010, 20:40, closed)

Tried that.
Tried saying if he was right and we were staying on earth cos it's spinning, we'd all be stuck to the atmosphere not the ground, too. He just said I was wrong.
( baw__bag contains traces of nuts on, Fri 19 Mar 2010, 20:41, closed)

Eurgh!
You got a stiffy from talking about the moon?! Pervert.
( Dervel OTBC, Fri 19 Mar 2010, 10:07, closed)

Cola=cubes flavoured shots.
They are as vile as they sound, but a lady had bought a round so we had to drink them :(
( baw__bag contains traces of nuts on, Fri 19 Mar 2010, 20:37, closed)