Quoth watchwolf49 :
Not sure this is correct … unaccelerated flight in the vertical would have to be in the absence of gravity. As long as the force of gravity is being applied, a 747 must create it’s lifting force. When lift > gravity, the plane goes up, when lift < gravity, the plane goes down. I understand that you’re applying of Newton’s second law of motion, but you have to include all the vertical forces involved. Gravity is constant, so the pilot can only adjust lift to adjust his altitude.
No, Xema had it right. When the net force is zero (that is, when your lift is exactly equal to the weight), you have zero vertical acceleration, which could be level flight, ascending, or descending. If your net force is positive (lift greater than weight), you’ll accelerate upwards, and if it’s negative (lift less than weight), you’ll accelerate downwards. Your motion may or may not be in the same direction as your acceleration: For instance, when the Vomit Comet is flying its arcs, it has zero lift and therefore downward acceleration, but it’s still going up at the beginning of the arc (it also needs to have some periods of upward acceleration at other times).
gnoitall:
obPedant: the critical plot element was not the gravity or mass of the titular neutron star, but the tidal forces caused by the neutron star’s steep gravitational gradient at close approach
I don’t see the connection to how much a cloud masses (or weighs). Maybe I lack imagination that way.
I didn’t think of Neutron Star either. I did think of The Integral Trees, which has tidal based “gravity” and atmosphere, after your post.
CurtC:
I hadn’t heard that joke, but a long time ago I heard the puzzle “which is heavier, a pound of gold or a pound of feathers?”
Of course everyone here would already know that a pound of feathers is heavier.
I wonder if there was confusion over this joke that got the other one rolling.
Mtgman
August 30, 2014, 6:33am
25
In another way to look at this, What if a rainstorm dropped all of its water in a single giant drop?
We’ll imagine our storm measures 100 kilometers on each side and has a high TPW[Total Precipitable Water] content of 6 centimeters. This means the water in our rainstorm would have a volume of:
100km×100km×6cm=0.6km3
That water would weigh 600 million tons (which happens to be about the current weight of our species). Normally, a portion of this water would fall, scattered, as rain—at most, 6 centimeters of it.
In this storm, all that water instead condenses into one giant drop, a sphere of water over a kilometer in diameter. We’ll assume it forms a couple kilometers above the surface, since that’s where most rain condenses.
The drop begins to fall.
Enjoy,