MrMongoose

I have no evidence to support my theory, but I believe that the universe exists continuously to infinity in both directions of time. No God or nothing involved at all if I'm right.

Disappointing. If only they went a bit faster!

If its in a vacuum how do you suppose this experiment is not going to work? If it doesn't have a question mark how do you suppose a question can work?

I think basically I've been hanging onto a simplification my sixth form maths teacher made for too long, and a lot of ponderign has set me straight! Thanks for letting me think out loud!

I do mean that, but I don't feel you addressed the bit thats getting me. I DO understand that all the sand that was on the conveyor before the point in time we look at it is irrelevant as its momentum is constant and that if we look at elements of sand as theyre added we get the right answer, and I don't dispute that. At the same time, I don't see why a line of sand cant be modelled as a particle at its centre of mass (which moves at v/2) with mass equal to the total mass of sand. Is that not similar to modelling a rod that undergoes no moments as a particle in a dynamics problem such as a rod falling through the air under the air at terminal velocity?

Well my previous argument holds as far as I can see other than that I forgot the second velocity should also be halved, which leads to a power of 3W. Another argument taking analogy from a jet in fluid dynamics gives me the popular 12W. The two should be the same though. Could someone please very precisely tell me why my first argument was wrong and revive my faith in fluids?

Horizontal speed is equal to the secant of the angle of elevation of the velocity. The rest is simple equations of motion, available at any good amths teacher.

Give me a minute. I just came up with another argument that gives me 12W. Got to work out which is wrong:confused:

I don't think a physics teachers unjustified answer is more important than Newtons laws, but yeah 12W. On second thought.. If you think about it, the sand has one end at a distance v.t away from the sand input, and the input is always at 0, so the centre of mass of the sand as a whole will be half way between the two and the velocity of the centre of mass of the sand will be half the conveyor velocity. [math]F= \frac{d}{dt}p = \frac{d}{dt}mv[/math] Thats with v the conveyor velocity. Lets call the sand velocity u. [math]F= \frac{d}{dt}p = \frac{d}{dt}mu=\frac{d}{dt}\frac{mv}{2}[/math] If you folow the rest as above, the constant of a half will just fall through all the steps leading to power=6W.

"I turn away with fright and horror from the lamentable evil of functions which do not have derivatives"- Charles Hermite

I thought she said she understood the maths relating torque to force amongst other things. Explanations such as "you can stop a toy car wheel but not an oil drill so the drill has more torque" (there have been many so I'm not just getting at you yt2095) just exemplify the mathematical principles. If you need more force at a greater distance from the exis of rotation, you have a bigger torque is just another way of saying T=Fr (or whatever vector equivalent you want to use).

Ok, I'm trying to think of more and more complicated ways to explain it:cool: Imagine it in terms of an elastic shock wave in a solid. If you apply a force to the side of an object, the part immediately being pushed will compress, allowing the solid boundary to move in the direction of the force. The part immediately behind that will then compress to allow the first element to return to its initial shape, but as the nearest part of the first element has moved and then the element returned to its initial shape, the furthest part of the element has also moved. This shock wave will propogate from element to element, causing them all to eventually move a short distance in the direction of the force. Similarly with torque, if you twist one annular ring of a disc, there will be a shear stress rather than a normal stress, but a similar "wave" will propogate to all other elements within the disk away from the annulus. Thats what torque is.

I object to the answer to number three

I have this really annoying assignment where I've been told to pick a component from an existing machine and then analyse the likely stresses using traditional pen and paper methods, then using a finite element approach to compare the results. I need help thinking of a component complicated enough to turn my lecturer on. Any ideas?

Pressure and temperature wont be high because of the 10km flame?

As a complete guess I'd say the heat generation withing the material is proportional to the rate of change of magnetic flux.

Burn rate is a function of composition, pressure and temperature, so we're one closer than that

Well The torque is generally colinear with the rotation. Yourdadonapogostick said the rest.

The rotation is actually perpendicular to the plane of the force and the rotation.

Another way to think about it is just to think of a simple bending beam. If you rotate one end by applying a force, it bends, and thuscompared to a neutral unstretched axis, one side is stretched and the other is compressed, so they will provide moments by virtue of Hookes Law onto whatever is attatched to the other end (or equally back to the source). You can kind of follow a pseudo-inductive path through the system as a whole. Yet another way of looking at it is to grab a ruler in one hand so that the tip of your finger is on top of it at the one end and your thumb holds it up about 2 inches along the underside. Now apply a force to the other end with your other hand, and two discrete forces will act on your finger and thumb. Torque is just the sum of all those forces internally between atoms along the ruler.

I have this awful affliction where I can't look at someone's avatar without assuming it's them... You means she's not Dexter?

Well yeah, vectorially. But as I missed off the vector arrows, I was clearly talking about the scalar magnitudes, sheesh I was just trying to appeal to the high school nostalgia in him. I'm sure it's not as patronising as telling him to use a wrench and "feel" the torque!

It's just a complex pattern of shear stresses, which means sliding layers within a crsytal over each other and in doing so, seperating atoms slightly, which means electromagnetic force. All the T=Fr stuff just comes from summing all the seperate contributions. If you're looking for something more fundamental then you wont find it because torque really isn't that fundamental.

You forgot to mention [math]p=\rho[/math]

Is it that easy to put standard desktop type cd drives into laptops? Especially with this thing being so old... did they even use the same buses back in 1996? This is more difficult than I thought it would be.. I'm not against using the same disk 5 times in a row. It seems that there are tons of distributions that will run off the floppy but not let you set it up on the hd itself. And getting fortran on is looking like a problem too. I'm angry now... no more laptop for a day or so :@