Your descriptions are the very reason many of us don't like 'centripetal
force'. You are now using centripetal and centrifugal to refer in general
to forces pointing inwards and forces pointing outwards regardless of the
motion of the reference frame or the acceleration of the object. This is
why reserving 'centripetal' for the accelerations that 'cause' uniform
circular motion (or any portion of such) should not be carried over to
'centripetal force' since then talking about a 'centrifugal force' implies a
centrifugal acceleration which you will have more difficulty in identifying
for the crust of the earth or the 'surface' of the sun, since now the net
forces are zero.
Rick
----- Original Message -----
From: "Kilmer, Skip" <kilmers@GREENHILL.ORG>
No, actually I know the ball has a net inward force, provided by the string.
The reaction force is on the string, not the ball. Without the ball pulling
it outward, the string would likely hang more nearly vertical, since its
center of mass is closer to the center of the circle. I'd need more time to
look at the dynamics of the string to say for sure, but I know, and think I
stated below, that the N3 forces are applied on different objects, ball and
string.
The centrifugal force on the earth keeps it from falling to its center, not
the sun, and results from molecular forces holding the crust on top of the
mantle, etc. Similarly there are centrifugal forces on the sun (radiation
pressure) that keep it from collapsing under its own weight.
In the rotor, I am pushing outward (centrifugally) on the wall, as could be
shown by having me back up to a scale.
skip