The Physics of Superheroes: Spectacular Second Edition by James Kakalios Page B

stop. This force is still large enough to often knock the driver unconscious, but the important point is that it is no longer lethal. The right-hand side of the above equation is determined by the crash—you were moving at 60 mph and then you came to rest because you hit something. If you wish to avoid this, you shouldn’t have hit anything. Your mass in the expression for the change in momentum does not change (this is the best-case scenario!). Thus the right-h and side of the equation is governed by the collision, and all you can do to minimize the damage is through control of the left-h and side, that is, the impulse. The product of force and time must always be the same, as the net result is the same—namely, the initial large momentum changing to zero. The longer the time in a given impulse, the smaller the force needed to bring about the change in momentum. This is also the physical justification for a boxer rolling with a punch, increasing the time of contact between his face and his opponent’s fist, so that the force his face must supply to stop the fist is lessened.
    Now, Spider-Man’s webbing does have an elastic quality, which is a good thing for Gwen Stacy, but the time that is available to slow her descent is short, which is an awful thing. For a given change in momentum, the shorter the time, the greater the necessary force. For Gwen, her change in speed is 95 mph-0 mph = 95 mph, and assuming she weighs 110 pounds, her mass in the metric system is 50 kilograms. If the webbing brings her to rest in about one half of a second, then the force applied by the webbing to break her fall is 970 pounds. Hence, the webbing applies a force nearly nine times larger than Gwen’s weight of 110 pounds. Recalling that an object’s weight is simply W = mg, where g is the acceleration due to gravity, we can say that the webbing applies a force equivalent to 9 g’s in a time span of 0.5 seconds. As indicated in fig. 6, when the webbing brings Gwen to a halt, a simple sound effect drawn near her neck (the “SNAP!” heard round the comic-book world) indicates the probable outcome of such a large force applied in such a short period of time. In contrast, bungee jumpers allow a distance sufficient for the cord to extend for many seconds, in order to keep the braking force below a fatal threshold.
    Traveling at such a speed, coming to rest in such a short time interval, there is no real difference between hitting the webbing and hitting the water. However, there have been recorded cases of people surviving forces greater than that experienced by Gwen Stacy. Col. John Stapp rode an experimental rocket sled in 1954 and was subjected to a force of 40 g’s during deceleration, yet lived to describe the experience as comparable to “dental extraction without anesthetic.” Of course, Col. Stapp was securely strapped into and supported by the sled in a reinforced position. More typically, suicide victims who jump from bridges die not from drowning, but rather from broken necks. Hitting a body of water at such a speed has the same effect as hitting solid ground, as the fluid’s resistance to displacement increases the faster you try to move through it (we’ll discuss this further in Chapter 4 when considering the Flash). Tragically for Gwen Stacy, and for Spider-Man, this is another example of when comic books got their physics right, and we readers were not required to suspend our disbelief, no matter how much we may have wanted to.
    Spider-Man seems to have learned this physics lesson concerning impulse and change in momentum. A story in Spider-Man Unlimited # 2, entitled, appropriately enough, “Tests,” finds the wall-crawler adhering to the top of a skyscraper when an unfortunate window washer plummets past him. Launching himself after the falling worker, Spider-Man must solve a real-life physics problem under more pressure than you’d find in a typical final exam. As he closes the gap between the worker (due to the fact