Defying the Laws of Physics


Eddie sez:

I was in two units in the United States Air Force where regulations, just about all of them, were waived. The mission was so important, we were told, that if we needed to deviate from a rule or regulation that we should use our best judgement and press on. The problem is that not all pilots possess the same high level of judgement and sometimes that is just in the eye of the beholder.

Quite often the other pilot would say "that's waived," when it just couldn't be. I often replied, "you can't waive the laws of physics." But not everyone understands this. Why? I blame the movie Superman. We saw this in a theater when it was the number one box office hit. At one point Lois Lane is falling from atop the Daily Planet office building to her certain death. Superman changes into his tights and soars up to catch her. (Video: Superman Catches Lois) At that point I said, too loudly I guess, "Now she's twice as dead."

My fellow movies goers didn't appreciate that.

Well, as it turns out, I didn't figure that only falling half the distance her velocity would be reduced almost by the factor of Superman's velocity upon arrival halfway up the building. So she isn't twice as dead, she is slightly more dead. (260 G's in Superman's arms versus 250 G's on the pavement.)

Why is this necessary? See: Decision Making .

Last revision:


Defying the Laws of Physics


Given: Empire State Building height = 1250'

Assumption: The Daily Planet Building = 1/2 Empire State Building = 625'

Formula for distance fallen d due to gravity for a given time t:

d = ½ g t2

Time for Lois Lane to fall from top to bottom of the building:

t = 2d g = 2(625)ft 32ft/sec² = 6.25 seconds

Time for Lois Lane to fall from top of the building to Superman's arms (halfway down):

t = 2d g = 2(½)(625)ft 32ft/sec² = 4.42 seconds

Velocity v at time t while falling:

v = g t

Lois Lane's velocity at ground impact:

v = g t = (32ft/sec²) 6.25  seconds = 200  ft/sec

Lois Lane's velocity when caught by Superman:

v = g t = (32ft/sec²) 4.42  seconds = 141.44  ft/sec

Formula for distance covered d when accelerating at a for a given time t:

d = ½ a t2

Given: Superman's time to reach Lois from ground = 10 seconds

(Timed from video = 20 seconds, figure this is doubled for dramatic effect, so actual time should be half.)

Superman's acceleration to half-way up the building:

a = 2 d = ( 2 ) ( ½ ) ( 625 ) 10 2 = 6.25  ft/sec²

Superman's velocity at half the distance to the top of the building:

v = a t = ( 6.25  ft/sec² ) ( 10  seconds ) = 62.5  ft/sec

Given: Distance from Lois Lane's head to her feet: 5 feet

Time for Lois Lane's head to hit pavement once feet hit:

t = d v = 5 feet 200  ft/sec = 0.025  seconds

Time for Lois Lane's head to reach her feet if caught by Superman:

t = d v = 5 feet (141.44 + 62.5  ft/sec = 0.0245  seconds

Lois Lane's G-Load on impact with concrete:

a = v gt = 200  ft/sec (32  ft/sec²) 0.025  seconds = 250 G

Lois Lane's G-Load on impact with Superman:

a = v gt = (141.44 + 62.5 )  ft/sec (32  ft/sec²) 0.0245  seconds = 260 G

See Also:

For more about the mechanics and physic used here, see Mechanics.