The term is action-reaction force pairs.
From: Guag Meister <[EMAIL PROTECTED]>
Reply-To: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: Re: [Biofuel] Canadian Trash
Date: Mon, 25 Oct 2004 22:19:16 -0700 (PDT)
Hi Eric ;
Eric wrote :
> I really don't understand this assertion. (And I saw
> it on the web pages from scientists as well.) Saying
> that the force is an illusion. If you put a spring
> between my hand and the ball it would compress. A
> spring needs a force pushing it from both ends to do
> that. No exceptions.
This is a good question. I guess that the word
illusion is maybe not a good choice, in that you feel
it. But your hand is supplying the force to the ball.
not the other way around. Your hand by itself
couldn't do it anyway. Your hand is connected to your
body which is connected to your feet which are
hopefully stationary on the ground due to friction of
your shoes. When you push the ball, the force you are
suppling to the ball is transmitted in the opposite
direction to your feet and ultimately to the earth.
The earth will move slightly in the opposaite
direction (like 1e-20 meters, depending on the
acceleration of the ball).
I have yet another way to describe this. Let's say
you are standing on the earth and you fire a bullet
horizontally. What happens? The bullet wants to go
straight, but it is acted on by gravity. So it begins
to fall toward the surface of the earth while moving
at high speed horizontally. Now the surface of the
earth is curved, so as the bullet moves horizontally a
lot and falls a liittle, the surface of the earth is
"falling away" from the bullet due to the surface
curvature. There is NEVER any centrifugal force.
What is happening for an object in orbit is that the
object is "falling" towards the earth exactly as fast
as the surface of the earth is "falling" away. The
object moves horizontally and falls a little. The
surface of the earth has fallen a little. When these
two rates are exactly equal, the object is in orbit.
If someone went up to 100 miles and dropped a stone.
It would fall straight down due to gravity. If you
threw it horizontally at 100 mph it would fall in a
curved path and land a few hundred miles from you. If
you threw it at 1,000 mph it would land much further
from you. If you threw it at 16,500 mph it would
almost make it around the earth before landing. If
you threw it at exactly the right speed (approximately
17,500 mph for near earth orbit), it would be falling
at exactly the same rate as the surface of the earth
is "Falling". If will never land, ie. it is in
orbit.. There is NEVER any centrifugal force. Only
centripital force of gravity, directed toward the
center of the earth, which is causing the curved path.
If you threw it faster than 17,500 mph, say 18,500
mph, the centripital force of gravity would not be
enough to curve the objects path fast enough to stay
along the curvature of the earth, and the object would
move further into space. This is NOT centrifugal
force. It is insufficient centripital force.
Autronauts in orbit are weightless because they are
continuously "Falling" (ie. accellerating towards the
earth due to gravity). They feel just as you would
feel if you were in an elevator and someone cut the
rope. When you accelerate at g towards the earth you
become weightless. The astronauts are "falling" ALL
THE TIME. They just happen to be moving horizontally
fast enough so that the surface of the earth curves
away from them so the never hit it.
Whew! Hope this helps.
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