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February 11
Work? Force? Help!
Hello. So i'm a highschooler in a physical world science class. We are studying work (the force required to move something)
Basically i'm confused about this whole subject. does it have to do with gravity? how do we measure force?
Well I was assigned the investigative quesion "Would it require more work to pull a brick along a flat surface or an angled surface?" If you could give me some info to help me find the answer it would be greately appreciated.
03:14, 11 February 2007 (UTC)03:14, 11 February 2007 (UTC)
Way to confuse the poor kid! OK - so work is force times distance. So if you have to pull the weight twice as far - it's twice as much work. If you have to pull it with twice the amount of force then it's twice the work. OK - so now we know what work is. How about force? Well, there are lots of different forces. To get a block to move along a surface, you have to provide enough force to overcome friction and to overcome gravity and to actually accellerate the block. If the ramp is level - then gravity doesn't enter into the picture - so the forces you need depends only on the friction and however much accelleration you are giving it. In these kinds of school-level problems they probably assume that the block only has to move exceedingly slowly - so we can ignore the effort to accellerate it from a standstill (that would be F = m.a - force equals the mass times the amount of accelleration). For the sloping ramp, you also have to include gravity. If you are pulling the block down the ramp - gravity provides some of the force - and depending on how steep the slope is and how much friction there is, you may not need to provide much (or perhaps any) force yourself - at any rate, the force you need has got to be less than for the level ramp. If you are pulling the block up the ramp - then you've got both friction AND gravity to fight - so the forces you need is more than for the level ramp. If you are pulling the block over the same distance in all three cases then we know that the work required will be more for pulling the block uphill, less on a level ramp and less still on a downward ramp. This is good because it's exactly what you'd expect. If your job is hauling bricks around - you know it's less work to pull them downhill than uphill...I mean...DUH! In the real world - there are lots and lots of other annoying considerations - friction is generally less when something is moving than when it's stationary - that 'accelleration' cost isn't negligable - the amount of friction depends on the slope of the ramp - if the block moves. it's going to get hot - and that will change the nature of the frictional forces....all sorts of annoying practical details get in the way of knowing the utterly correct answer - but for school project the don't want that kind of depth. SteveBaker 23:18, 12 February 2007 (UTC)
Grey Vs Gray
I would like to edit the heading for the 'Grey Matter' page; Grey should be spelt Gray as it is pertaining to a colour and not a family name. I have managed to edit all the 'greys'on the rest of the article but the title of the article as well as a diagram seem to be un-editable. How can I change it? Or can you change it please? Thank you.
Gun-to-Head Realism
So in just about every action movie ever made, some guy holds a gun to some guys head while guns are pointed at his own head. The premise of the conflict is that if the criminal is shot, even in the head, and even if he sees no sign beforehand, he'll have time to shoot his own victim before he dies. Is this at all realistic? Couldn't one of the poeple in this situation just pull the trigger without showing any sign beforehand and be certain he couldn't get shot back? I don't know which other desk might be better suited for this question. 70.108.199.130 04:57, 11 February 2007 (UTC)
Any info we provide about such topics is of course only for general interest and movie discussion, and is not intended to be practical advice for personal defense purposes. Wikipedia says simple reaction time is about 150 milliseconds for him to respond to the impact of the bullet or the sound of the shot by a trigger pull. (I have personally seen 100 msec simple reaction time). If the standoff participants are 10 feet apart, the bullet will travel ten feet in about 1/100 second, which is 10 msec. In the standoff described, if there were no possibility that the other gunman would agree to stand down, and he was going on like a movie badman about how he he was going to kill you right after he finishes his page of plot exposition dialogue, in other words you are completely sure he is eventually going to shoot you, and you have a sufficiently large caliber gun to completely mush his brain, I would shoot him through the brain and duck out of the way while emptying the gun at him. Negotiation is far preferable, but with his brain destroyed he cannot make an intentional trigger press, and odd are better any reflexive finger twitch depressing the trigger would fail to hit you than if he were allowed to fire a carefully aimed shot through your own brain. Of course you would say something to induce him to relax before you fired. Say "I'm giving you to the count of three to put down your gun. One.." (he relaxes), you shoot. You might also remark that he's going to have a hard time shooting you, because the safety on his gun is engaged (made you look). You would not want to give a visible "tell" that you were about to shoot. In other words, if you lose a lot at poker, being such a stone cold killer in the standoff is not going to work out for you. If it is not a standoff but just a person aiming a gun at another person, a judo instructor said that if the gunman is within easy reach, as is usual in movies and TV for composition and dramatic purposes, a trained martial arts fighter has a chance (but by no means a certainty) of grabbing the gun hand and sidestepping or turning so that when he pulls the trigger you are no longer in front of the gun. Then the martial arts expert can open the big can of whupass. But this requires a movement executed in the aforementioned 100 or 150 milliseconds, and even he said that he would not attempt his if it were a simple robbery. Just give him your watch and your wallet and don't wind up a dead hero. The average citizen would not succeed in the disarming attempt. A smart gunman would stay out of reach, and try to get his victim in an offbalance posture to prevent any sudden lunges (I guess that's why cops bark instructions for suspects to get in certain offbalance positions.) Edison 17:54, 12 February 2007 (UTC)
- We have an article on the Mexican Standoff. Lowerarchy 15:54, 14 February 2007 (UTC)
Was there ever a live test of an ICBM?
I'm wondering if any country ever actually launched an ICBM with a live warhead(s) that detonated after reentering the atmosphere? I know about Starfish Prime, but I'm more interested in seeing something like the famous Peacekeeper MIRV picture, but with mushroom clouds at the end of the lines. Thanks! --TotoBaggins 05:05, 11 February 2007 (UTC)
Joint Pain
I am suffering from joint pains for a long time.Also I will be having muscle pulls easily.Sometimes, while playing cricket I had serious pain in my thumb and it will swell up and remain black for some days.What may be the probable reasons for my problems.
ques. about blood
why impure blood is bluish? —Preceding unsigned comment added by Arunbrainy (talk • contribs) 07:31, 11 February 2007
ques. about sex
can i have milk if I suck unmarried girl's breasts/ —Preceding unsigned comment added by Arunbrainy (talk • contribs) 07:33, 11 February 2007
Do you really think lactation is influenced by marital status? alteripse 15:34, 11 February 2007 (UTC)
Hormonal abnormalities (a pituitary tumor) can cause lactation in women (or men). So it might happen. An unmarried girl might also be a new mother (it does happen). Edison 17:23, 12 February 2007 (UTC)
Perhaps Breastfeeding#Lactation without pregnancy is relevant. (SEWilco 18:48, 14 February 2007 (UTC))
ques. about earth ..arun
why earth moves? —Preceding unsigned comment added by Arunbrainy (talk • contribs) 07:35, 11 February 2007
GB 08:42, 11 February 2007 (UTC)
According to Kepler the earth moves because the rays of light from the sun hit it in such a way that it is pushed sideways, but also moves round the sun instead of away due to huge magnets in both the sun and the earth:)Hidden secret 7 13:10, 13 February 2007 (UTC)
Casimir problem for weinberg
I recently heard about an arguement between two scientists about the level of energy in the Zero point energy field. Dr Steven Weinberg claimed that there was not all that much about, yet according to a recent page i read at physics web the zpf can produce pressure on casimir mirrors in the nanometre range of about 1 atmopshere thats kgs per cm 2. Wouldnt it take a large amount of EM waves to produce this much pressure. The article isnt loading at the moment on my pc, but look the casimir effect page
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