Derren said:
According to the D&D rules you fall 150 ft. the first round and 300 ft every round after that.
Assuming a six-second combat round and no air resistance, IRL you would fall 32 feet per second per second until reaching terminal velocity, or 32+64+96+128+160+192 = 672 feet within that first round. Obviously, our stalled flier is still using its abilities to slow its descent. See also this wiki article,
http://en.wikipedia.org/wiki/Terminal_velocity, which includes this tidbit:
For example, the terminal velocity of a skydiver in a normal free-fall position with a closed parachute is about 195 km/h (120 mph or 54 m/s). This velocity is the asymptotic limiting value of the acceleration process, since the effective forces on the body more and more closely balance each other as it is approached. In this example, a speed of 50% of terminal velocity is reached after only about 3 seconds, while it takes 8 seconds to reach 90%, 15 seconds to reach 99% and so on.
Higher speeds can be attained if the skydiver pulls in his limbs (see also freeflying). In this case, the terminal velocity increases to about 320 km/h (200 mph or 89 m/s), which is also the maximum speed of the Peregrine Falcon diving down on its prey.
In D&D 3e, the combat round is broken down into actions occurring at various points in that 6-second window. In order to prevent our friend from hitting the bottom of the 100-foot shaft, our spellslinger must make a
web within an approximate 2-second timeframe between the fall and the splat.
However, in D&D, we also know that creatures like dragons can fly and that falling does a lot less damage in some cases than it does IRL. It is therefore not unreasonable to assume that there is more air resistance in a D&D world than in the real world. This means, if accepted, that objects fall more slowly in the game than IRL. In other words, the spellcaster has more than 2 seconds to react.
But in D&D you can normally change your stated action based upon the actions of others, so fast reaction times are the order of the day. The question is, can the spellcaster cast his spell before his friend meets the bottom of the shaft? The DM might be fair in saying that a readied action is needed; I would certainly argue this if the shaft was shorter. The DM might also argue that, if there are 20+ different "counts" in the initiative cycle, that each one must therefore occupy less than a second each. Then the only question is, how close is one init to another? This seems reasonable if the pit is long enough (at least to me).
In any event, as I said, I'd have allowed it.
YMMV.
RC