Path: ccsf.homeunix.org!news.moat.net!tiscali!newsfeed1.ip.tiscali.net!border2.nntp.ams.giganews.com!nntp.giganews.com!news-in.ntli.net!newsrout1-win.ntli.net!ntli.net!newspeer1-win.ntli.net!newsfe7-win.ntli.net.POSTED!53ab2750!not-for-mail From: "Simon" Newsgroups: fj.life.in-japan References: <86c1g1d8nhrhqc18sg2phhdqgdg6mhi8fk@4ax.com> <1124121627.347317.199850@g14g2000cwa.googlegroups.com> <1124125095.296052.93400@f14g2000cwb.googlegroups.com> <1124147664.781177.276080@g44g2000cwa.googlegroups.com> Subject: Re: Does this count as irony? Lines: 62 X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-RFC2646: Format=Flowed; Response Message-ID: Date: Tue, 16 Aug 2005 20:33:53 GMT NNTP-Posting-Host: 213.106.145.37 X-Complaints-To: http://www.ntlworld.com/netreport X-Trace: newsfe7-win.ntli.net 1124224433 213.106.145.37 (Tue, 16 Aug 2005 21:33:53 BST) NNTP-Posting-Date: Tue, 16 Aug 2005 21:33:53 BST Organization: ntl Cablemodem News Service Xref: ccsf.homeunix.org fj.life.in-japan:28837 "Paul Blay" wrote in message news:ddtgvl$1t5$1$830fa7b3@news.demon.co.uk... > "Gabor Farkas" wrote ... >> Simon wrote: >>> http://www.abc.net.au/science/k2/homework/s95523.htm >> >> sorry, but this is...hmm...i wonder if he really does not know it, or he >> is trying to explain it using simpler terms and because of that he says >> something wrong.... > >> and since when does the weight of an item affect the speed of it's fall? > > "depending upon the weight and shape of the bullet." > > Actually his comment is fair as long as you include _size_ as a component > of shape. That's a bit dubious but it also works if the bullets are of > about the same density. > >> yes, the explosive gases maybe represent a greater force, but they stop >> affecting the bullet after it left the gun. on the other hand, the >> gravity affects the bullet the whole time. > > "The suck of gravity is not as powerful as the explosive gases that push > it out of the barrel. So it will accelerate to a maximum speed of not > 3,000 kilometres per hour, but somewhere between 330 and 770 kilometres > per hour" > > Again this is poorly phrased but if you look at it this way ... > The "explosive gases", against any resistantive forces (e.g. side of gun > barrel) accelerate it to 3,000 km per hour by the time it reaches the end > of the barrel. > > The maximum speed from /gravity/ will depend on the gravitational force > equalling the resistive force from air. This is where the "330 to 770 km > / hour" > bit comes from. > Now the trick is (which I don't know the answer to) how does bullet > velocity vary with muzzle length? The longer the muzzle the greater time > the gas can act on the bullet to accelerate it but also the force from the > gas will decrease the further the bullet is along the muzzle. > > If the bullet has ceased, or almost ceased, accelerating by the time it > reaches the end of the muzzle then his statement is a lot more accurate. > > So although you're right about the relative time that the forces apply to > the bullet the final velocity (down) doesn't depend on the muzzle velocity > but (given a few assumptions, including that it is fired directly up) will > depend > solely on the bullet density, weight and shape. Also the muzzle velocity > (up) /could/ be that where the gas force is equalized by the resistance > forces. In which case he might validly compare 'force with force' instead > of 'impulse with impulse' > > If I was going to bet though I'd bet that the bullet hasn't reached > constant velocity at discharge from the muzzle - No doubt some U.S. poster > will know all the ins and outs of it. ;-) The muzzle velocity isn't important, just the velocity of the bullet on it's way back down.