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Re: Nitpicking: gravity is not a force???



Hi Friends, let me join with some statements that may clarify or complicate
more your issues:
I will adopt a Newtonian point of view, actually was Newton who first
described mech. forces of nature in a close way: F=3Dma
Gravity is a force, that is: Force of Gravity, (Gravity means property of
bodies that have weight [gravido: in Spanish-Modern Latin], by the way:
Inertia concept also derives from bodies with weight, and velocity, busy
moving or staying at rest, but always showing a dislike to be disturbed in
their duty) .
Force excerted between massive bodies ( Interaction forces between bodies
that have mass: full of matter).
Yo need to have a mass to feel these forces, then you end up having a
weight at the place were there is such a force interchange.
All natural forces are mechanical, but we like to describe them as coming
from "different origins"according the peculiarities of the masses and the
particular way they interact. At least, at the present state of Physics we
distiguished four different "origins" or interactions.These forces spreads
out as fields (Forces per unit "mass"), To sense such" fields of forces"
you need a test "mass", or charge, or dipole, or... or whatever equivalent
particular "mass" with the same specs. like the one you assume generates
the field. On the other hand, the concept of field is a mind invention
(Faraday), usefull to describe these spreads, and fill the empty space with
something. All this forces can be and are measured in Newtons.(Period)
Some of them are atractive only (Grav.) others can be attractive or
repulsive.(Peculiarities).Some of them are long range, some others very
small.But they are always there.
Gravity looks to be constant for us, because we live in a potential surface
( Earth surface: g, that is not the force, but the acceleration of gravity
and is aprox 9.7.......(Only in a particular place in England is
9.81........]. with small variations from point to point "on" earth surface
and during day and night, etc) and is the one you will be feeling when you
multiply it with your body mass, when you drop in a not to deep hole and
will tray to evaluate the impact force.( You calculate v=3Dg.t1[ flight
time], then m.v=3Df.t2 [ t2=3D impact time],then estimate impact time in
miliseconds and you get the smashing force! generated with your body at the
time of contactdue to GRAVITY, when you reach the hole's bottom). If you
are not falling in a hole but are just standing, knowing g, you multiply
it by your mass and get your weight in Newtons!( The force your mass
generates when it interacts with the earth gravity force) and gets
cancelled on the contact surface of your shoes when you are standing up.
As its was said by Betty, Forces of Nature are Gravitacional,
Electromagnetic,Weak Interactions, Strong Interactions.Last news is that we
reduced them to three, and Hawkins said recently to Clinton that we will
end up having only one in the next century.( One common origin for the
four forces).
=46orces are forces, and likes to spread "like" fields."You" have to get int=
o
the field( of forces) to sense them.( You think your students will digest
these considerations?)

At 9:08 PM +0800 8/8/6, Lim Ai Phing wrote:
Mervin Koehlinger wrote:
I agree wholeheartedly with you. I studiously avoid the use of the phras=
e
"force of gravity" in my physics classes for the exact reason that you
state: it leads students to think that it is always the same magnitude,
even though they can calculate that it isn't.

Jorge A. Trench
Avenida La Plata 165 : 2=B0,"2"
Buenos Aires C.P. 1184
Republica Argentina
Tel: 54-1-983-2919
e-mail: jtrench@ overnet.com.ar
=46ax:54-1-901-7521