MrMongoose

Surely if the big bang waas a single event, the universe would have no reason to expand. I've always thought of the big bang as an ongoing process at the centre of the universe.

It may be fun and educational and even possibly serve a practical purpose. It will cost money, require time and may be dangerous.

Pro: If you can charge it from a wind turbine or solar cell, it will contribute to global warming less than a traditional gunpower gun

The same reasoning that gives tyres (tires) without tread more grip on dry roads- e.g. slicks used for F1 racing on dry days. Greater surface area means higher coefficient of friction. As you stated above, the water on the road is what causes the tyres to slide (hydrodynamic lubrication), and having slots in the tyre allows water to escape so that the tyres can grip with the ice itself. Even where there is no water by virtue of surface melting due to solar radiation, the heat caused by the friction on the tyres can melt the ice and provide a thin layer of water. So yes you're right that for all practical applications a tread is better for driving on ice. All I'm getting at is that the problem with driving on ice is that you're actually driving on water covered with ice and theoretically if you were to drive on pure ice with slicks you would have more grip.. I don't even know if its possible to have pure ice at the tyre/ice interface though. Basically I'm being fussy. Not going to design any snowmobiles with slicks

Euler's formula simply converts between polar and cartesian coordinate systems in a complex plane, and can easily be shown by expanding into power series. Even with hindsight, the elegance is mindblowing. Euler is definitely my favourite pure mathematician.

To me it sounds like a lot of physicists are putting all thier eggs in one basket when there's no conclusive evidence that (maybe at a level beyond a level beyond a level beyond a level of complexity below the effects observed in decay) decay is not deterministic. The most recently developed observations always appear to be stocastic, and it never turns out to be the case. Or maybe it does.. we just don't know yet!

How can anyone other than someone with far too much money and the desire to do nothing but hop from blog to blog justify using so much RAM just on an OS?!

Tyres with a flat featureless face have more grip on ice than those with "grip". The problem is that it's impossible to drive over ice without melting it and then youre driving on water anyway.

This seems like the type of question which probably either has a stupidly trivial answer that will make me blush or a stupidly complex answer that will make me sexually aroused... Why does air consist of 79.1% nitrogen, 28.9% oxygen , 0.1% argon and a few other things (or something like that) at sea level rather than there being a distinct level of mainly carbon dioxide with a layer of oxygen on top then a layer of nitrogen on that and a layer of argon on top with other lesser things between? Is it just simply down to wind? If I fill a jar with air then leave it, could I later open it and remove different gases in a variation of fractional distillation?

[magnitude of] Just to be clear

OH. I thought he was comparing the second and third cases to each other rather than to the first case... I need to work on my English!

But "going up and slowing down" implies a downward acceleration, as does "going down and speeding up".

But both accelerations are implicitly in the same direction as g, so the force on the scale should be the same in both cases...

That what I said, centripetal force is equal to weight, not centipetal acceleration as gareth said, so the m's cancel. If it were acceleration, we would be left with an m in the weight term. I was being very stupid with the energy admittedly :$

By far the main difficulty with wood is the fact that it only comes in one shape and you cant melt it down and remould it

If you actually knew what you were talking about you would have bolded "more of", rather than highlighting your oppositions point...

The purpose of life is to increase the rate of entropy production of a system (lets say a planet), i.e. if the circumstances are right, not living is against the Second Law. As long as the resources exist to support life, life will exist to destroy those resources.

I'm not happy to be honest... The conversation as I see it goes like this: "Why do atoms like to lose energy?" "To become stable" "So why does losing energy make them stabler?" "Because particles like to lose energy" As compelling as the circular argument may be, it does little to explain why low energy states are stabler than high energy states. Sorry if I'm being awkward, but Herbinator asked a question I only just realised I wanted to know the answer to!

Just plain not true. I'm balancing weight with centripetal FORCE as well I should. You sure Swansont? I thought the potential energy would be positive, and I seem to get the right answer. If increasing height made PE drop, wouldn't conservation make KE increase, so as you move upwards, you constantly accelerate?

Ah, so thats the velocity for an orbit along the surface! Well a few hundred metres below the surface, but im assuming thats because I worked to 3 s.f Cheers I can see where you get mg from now but how did you know the slowest muzzle velocity would correspond to orbit at the surface?

Fixed it now- any ideas?

Can someone tell me where I'm going wrong here? Parallel to the surface of the moon there will be no acceleration, so the initial horizontal component of velocity will be equal to the final horizontal component. The final component is given by equating the necessary centripetal force to the gravitational force, i.e [math] m\frac{v^2_h}{R}=\frac{mMG}{R^2} [/math], which is [math] v^2_h=\frac{MG}{R} [/math]. (M is the moon's mass, and m that of the bullet. v is velocity with subscript h being the horizontal component and G is the gravitational constant. R is the radius of the orbit). Letting subscript v denote the vertical component and r be the radius of the moon, conservation of energy can be applied- [math] m\frac{v^2_h}{2} + m\frac{v^2_v}{2} + \frac{mMG}{r}=\frac{mMG}{R} + m\frac{v^2_h}{2} [/math], or, [math] v^2_v = 2MG(\frac{1}{R}- \frac{1}{r}) [/math]. Now, the muzzle speed of the bullet is simply given by [math] v^2 = v^2_v + v^2_h= 2MG(\frac{1}{R}- \frac{1}{r}) + \frac{MG}{R} [/math] i.e. [math] v^2 = 2MG(\frac{3}{2R}- \frac{1}{r}) [/math] Which implies that R=3r/2 v=0, i.e. If im sitting here at rest in my chair now, that should be enough velocity to put me into orbit at 1.5x the Earth's radius.

I can't see where you posted that. You posted the escape velocity, with no derivation of the velocity needed for orbit following. The OP's question asked what velocity is required to cause orbit, there is clearly going to need to be a "vertical" component to overcome gravity to such an extent that when the bullet stops moving radially, a further "horizontal" component will give it the correct speed to orbit under the effects of centripetal acceleration at that radius. Is 1.7 therefore the minimum speed possible courtesy of pythagoras? If thats not how swansont and gareth did it, I'll see what my method gives when I get home.

How exactly do you derive it from escape velocity? I need to find myself a course in orbital mechanics if I'm ever going to get that job as a rocket scientist:mad: