motorgliders as towplanes

Dude!



You can pretend there is no gravity. You can pretend there is no air.

But there IS gravity, and there IS air.

Gravity is a downward force. Things move downward due to gravity,
including gliders.

But the question was not "what gives a glider motion?", it was "what
gives a glider FORWARD motion?"

Sorry, can't do it without LIFT. (don't forget drag either)

Three forces act on a glider. Not one, not two, THREE.

Answer to question again: The resultant force of lift added to gravity,
balanced by drag.

Cookie


At 12:53 19 March 2009, Doug Hoffman wrote:
Bob Cook wrote:
You can change the reference or axis system all you want, But then
you
also change the direction of "down".


Gravity acts downward and no other diredtion.


Lift plus grivity act together and form a resultant force parallel to
the
direction of flight. Drag acts in the opposite direction at equal
magnitude.

Gravity (alone) is not the force that provides forward motion to a
glider.

Maybe we are wordsmithing/semanticizing a bit. Take away gravity and
air movement and place a glider somewhere up in the still air (I know,
suspend disbelief for a moment) and let go of the glider. No initial
motion is given to the glider, it is just "suspended in air". How much

lift and/or forward motion do we then get? None. Add gravity to the
same scenario and the glider will then move forward (after an initial
drop). So perhaps gravity *is* the sole force required for forward
motion. Of course we need air as well. But still air is a gaseous
mass, not a force or even a source of force. The reaction force caused
by the combination of gravity (sole source of force) and the presence of

air (air is not a force) leads to the forward motion of the glider.

Regards,

-Doug

Bob Cook wrote:
Gravity is a downward force. Things move downward due to gravity,
including gliders.

Aren't there some things that move upward due to gravity? Even upward and
sideways too?

But the question was not "what gives a glider motion?", it was "what
gives a glider FORWARD motion?"

Sorry, can't do it without LIFT. (don't forget drag either)

Three forces act on a glider. Not one, not two, THREE.

But isn't there only one potential energy field operative? Not two, or
three, just one? Didn't Aharonov and Bohm show that potentials are more
"fundamental" than forces, so that we should really be considering the
system using potentials?

Is somebody keeping score on the pedantry? I hope I got at least a couple
points!