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>>>> Is th ---2114655128-364004261-1348335327=:16378 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Yes Pat=0APhysics was always my favorite subject!=0AYou could get a top mar= k and know nothing.=0AIt took me a long way through school.=0AMade me doubt= the value of exams but that is another story.=0ASo long as you could work = out problems.=0ASolved a lot of tricky one at work too - helped my employme= nt record too.=0APhysics was great=A0=0AThanks for the reminder=0APaul=0A= =0A=0A=0A________________________________=0A From: Patrick Kelly <patrick.k= elly@dal.ca>=0ATo: naturens@chebucto.ns.ca =0ASent: Saturday, September 22,= 2012 11:28:15 AM=0ASubject: Re: [NatureNS] Correction; Fw: Velocity of lig= ht=0A =0A=0AI'm not sure I see the confusion arises over the kg being a uni= t of mass. I just covered this in my last astronomy class and why people us= e the words mass and weight interchangeably when they are two totally diffe= rent things. Mass is a measure of how much matter an object contains. You m= easure mass with a scale. A 1 kg bag of sugar has the same mass here as wel= l as on the Moon, as on a scale you would still need a 1kg mass to balance = it.=0A=0AWeight is a force, not a measure of mass. The problem is not helpe= d when people still use the English unit of "pound" for both weight and mas= s. The English system unit of mass is the slug, not the pound. Your weight = is the force of gravity acting on your mass and depends on your mass, the m= ass of the Earth and the radius of the Earth. if you are standing on the Mo= on (different mass and radius) you will "weigh" less because the gravitatio= nal force is less. If you stood on a doctor's scale on the Moon you would f= ind that your mass is the same as it is on Earth.=0A=0AIn the metric system= , the unit of force is the Newton (the symbol is N). 1 N is the force that = is required to accelerate a 1 kg mass at the rate of 1 m/s/s. (i.e. Force = =3D mass X acceleration).=A0=0A=0AAt the surface of the Earth, the gravitat= ional force =3D G x m x M / (r x r), where G is the gravitational constant,= m is the mass of a small object (like a person), M is the mass of the Eart= h and r is the radius of the Earth.=0A=0AIf you drop that small object, thi= s force will also produce an acceleration (because=A0Force =3D mass X accel= eration). So F =3D m x a. Since the force comes from gravity:=0A=0Am x a = =3D=A0G x m x M / (r x r)=0A=0ANote that since the small object is on both = sides of the equation, you can cancel it, and thus you get:=0A=0Aa =3D=A0G = x M / (r x r)=0A=0AThis acceleration gets a special symbol, g, and has a va= lue of 9.8 m/s/s (which you can round of to 10 m/s/s). This is the rate at = which all objects at the surface will fall (in a vacuum). If you go to the = Moon, since M and r are different the surface gravity there is much lower, = 1.7 m/s/s of about 1/5 that of the Earth.=0A=0AYou can also use the surface= gravity as a quick way to calculate your "weight" by multiplying your mass= (in kg) by g. A 1 kg mass has a "weight" of 9.8 N and a person such as mys= elf with a mass of about 100 kg would have a weight of 980 N. Thus a proper= metric scale would NOT be graduated in kg, but in Newtons. I expect there = are two reasons they don't. One is that most people would freak if their "w= eight" appeared to be 10 times what they thought it was, and secondly, sinc= e they assume you are using the scale at the Earth's surface, they have "co= nverted" the force back into "mass". Just don't take it to the Moon and exp= ect it to work properly!=0A=0APat=0A=0APS: For those who are curious, a mas= s of 1 slug has a weight at the Earth's surface of 32 pounds.=0A=0A=0A=0A= =0A=0A=0AThe kg a unit oef mass=A0=0A=0AOn Sep 22, 2012, at 9:58 AM, David = & Alison Webster wrote:=0A=0AHi Fred & All, =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0Sept 22, 2012=0A>=A0=A0Explanations of weight/ma= ss usually resemble inconsistent confessions obtained by torture but I gues= s that is ok now.=0A>=0A>=A0=A0It seems logical to me that weight should be= treated as a special case of F=3Dma where a in this case is g and F is mea= sured by exerting an equal and opposite force upward to keep the mass from = falling.=0A>=0A>=A0=A0One could then determine the magnitude of mass as F/g= and then proceed to work out units of momentum, inertia etc from there.=0A= >=0A>=A0=A0But unfortunately kg has been defined (or perhaps redefined) as = a unit of mass which leads to everything being a hopeless muddle.=0A>=0A>= =A0=A0I would try to reform the system of units dealing with weight, mass a= nd distance but I am tied up this afternoon.=0A>=0A>Yt, Dave Webster, Kentv= ille=0A>----- Original Message ----- From: "Fred Schueler" <bckcdb@istar.ca= >=0A>To: <naturens@chebucto.ns.ca>=0A>Sent: Friday, September 21, 2012 9:19= PM=0A>Subject: Re: [NatureNS] Correction; Fw: Velocity of light=0A>=0A>=0A= >=0A>Quoting David & Alison Webster <dwebster@glinx.com>:=0A>>=0A>=0A>>=0A>= I just dug out my 1st yr Physics (Weber, White & Manning, 1952) and =A0they= consistently refer to 'speed of light' as opposed to 'velocity =A0of light= '. Four other sources (1941, 1948, ~1965 &1962) have velocity.=0A>>>=0A>=0A= >>=0A>* indeed, it would be ineffective to purge society, or even =A0litera= ture, of all who misuse speed/velocity or weight/mass. Or, to =A0bring it c= loser to natural history, all who refer to nonhemipterans as =A0"bugs."=0A>= >=0A>=0A>>=0A>fred.=0A>>=0A>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=0A>>=0A>=0A>>=0A>----- Original Message ----- From: "= David & Alison Webster" <dwebster@glinx.com>=0A>>>=0A>To: <NatureNS@chebuct= o.ns.ca>=0A>>>=0A>Sent: Friday, September 21, 2012 7:44 PM=0A>>>=0A>Subject= : Velocity of light=0A>>>=0A>=0A>>>=0A>=0A>>>=0A>Dear All, =A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0Sept 21, 2012=0A>>>>= =0A>=A0The recent discussion about transmission of electricity, reading =A0= of HEAT and reading some of Energy... brings to the forefront a =A0question= that has nagged me for decades. Perhaps someone can clarify.=0A>>>>=0A&