Recent content by Hobnob

Thanks so much, that's exactly the kind of advice I was looking for! (And incidentally, this sounds like my original idea, before I panicked about the weight, so I'm pleased to hear it) Could you just clarify this bit - I can't quite picture in my head what you're talking about. Are you just...

Can you ask him if that would be ok? I found a couple of examples online, but one of them is built around a bloody great welded steel frame, which is a bit beyond me, and the other one seems to have been removed, leaving only some ghostly references... Ellison doors look interesting but I'm...

Thanks for the suggestion. The only problem with that is practical use - anyone wanting to go through the door has less than half the actual door width to play with. But you're right, that would make is easier. Re Ellison doors - oooh :) That looks interesting. I'll have to do a bit of...

Hi there I'm a complete novice about this kind of thing, but I've decided to fulfil a long dream of mine and make a bookcase with a secret door in it :) I've thought about various methods, but eventually I've figured that the best system would be to make it rotate around a spindle on one...

This is turning into more of a blog than a thread... I think I've solved it, with the help of a dodgy cached document on Google - thanks, Gernot Hoffmann! The solution is to replace tanh with coth and cosh with sinh when the initial velocity is greater than terminal velocity.

Okay, I've done some more research and found the answer to my original question (it was on wikipedia all the time, I just missed it). The function is: v = sqrt(g/r) * tanh(t*sqrt(g*r)), where r is a constant that depends on various factors that don't matter at this stage. This is easily...

Does anyone have a solution (approximate is fine) for the Drag equation? What I mean by this is that I need to be able to get position and velocity as functions of time for a body falling through air from rest. I managed this for a viscous liquid where drag is approximately linearly...

I know this is all pedantry anyway, but I guess my point was that for functions that trawl through search space (eg genetic algorithms or simulated annealing) what counts as an 'optimum' depends on what you ask it to look for. If I want it to find a root, I just ask it to minimise abs(f(x))...

I can't even understand the question. 'Shifting' how? Horizontally? Vertically? Are we talking about the boat getting a velocity? In that case, we need a time as well as a distance. If it's a vertical displacement, then we need the distances of the lovebirds from the centre of mass in order to...

A root *is* an optimum, isn't it? (it just depends on your utility function). But yes, any kind of numerical solver will do the job. The reason I'm thinking of using some kind of iterative method is that I suspect it's pretty close to reality: the voltage is applied, it creates a current, the...

Just following up on this, two further questions (slightly edited, because rereading it I realized I wasn't clear): 1) Does anyone have a link to some actual data on the resistance variation in an incandescent bulb? (and indeed in a diode, which I'm also going to have to do) I can't find it...

The distance to the Moon, as well as its radius, can be found by various triangulation methods. A simple example: At a certain time, you measure the position of the Moon from an observatory in Britain. At the same time, someone else measures the position from Germany. You know the distance...

I'm trying to work out the correct algorithm for using Kirchoff's rules when using a non-ohmic resistor like a light bulb. The problem is that the resistance depends on the voltage, but the voltage may depend on the resistance (a simple example: a bulb and a resistor in series: how should the...

Hi all Just come back from my holiday to find that my question has produced quite a lively discussion :) I haven't had a chance to look through it in detail, but just a couple of quick replies: Regarding lies-to-children: for those who don't recognise the expression, see Ian Stewart, Jack...

I read your comment at midnight last night, but when I was lying in bed I realized the point you were making. You're right, that should solve my problem - kind of obvious, thanks! Merry Christmas... Hob