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 Ceremony 11-11-2012 07:23 AM

Biology/Physics Question

I meant to post this in The Lounge a few days ago but it fits better here, so:

I was watching this X Files episode, and was wondering whether its take on the effects of what happens are true to life. The episode centres around a boy who is able to move at extremely high speeds, so fast that his entering a room and removing something from a locker is only half-captured in one frame of a CCTV camera. So fast the soles of his shoes melt.

He ends up in hospital and Scully is looking at his x-rays to see what's wrong with him. He has stress fractures in his bones, multiple concussions, Scully notes that he looks like he's played pro football for 15 years. He's in pretty bad shape.

My question though is focused on a scene where he's driving in a car with another kid, and he drives the car at 80mph towards a lamp-post, only to jump out and pull the other kid from the car before it hits the pole. Now considering that the kid who moves quickly can move without being seen - he essentially disappeared when he left the car - would pulling someone out of a car at that kind of speed not do them more damage than hitting a pole at a high speed would do? Especially since you wouldn't be braced for the impact and it's far beyond any sort of speed humans normally move at.

 Fugu 11-11-2012 11:55 AM

Momentum=mass*velocity

Change in momentum=force*deltaT, where delta T is the change in time associated with the change in momentum.

Therefore, m2v2-m1v1=Fdt, where m2=m1 is the mass of the guy in the car, v2=0 is the final velocity of the car and v1=80 mph is the initial speed of the car. We can get the force experienced by the guy in the car as a function of the time it takes for him to decelerate by rearranging the equation relating force, time and momentum:

F=-m1v1/dT

If the guy's mass is 100 kg, and the speed of the car is 80 mph = 35.8 m/s, then the force (in Newtons) that the guy experiences is

F=-3580/dT

If he decelerates in 1 second, the force is 3580 N, or 3.65g based on his mass.

If he decelerates in 0.5 seconds, the force and g level are both doubled to 7160 and 7.30g, respectively. Beyond this level, he is unlikely to survive.

 Unaffiliated 11-11-2012 03:50 PM

It's probably better to pull him out, assuming he pulls him out to the side of the car.

I'm pretty sure that hitting a pole at 80mph is basically automatic death.

link a video so we can see?

 Ceremony 11-11-2012 04:20 PM

There's actually a surprising lack of X Files videos on youtube.

Though when he pulls the kid out of the car he ends up at most 10 feet away, standing upright (not even off balance). The speed of him being pulled out is that fast you can't see it, he's in the car and in the next instant he's standing up.

 Unaffiliated 11-11-2012 04:33 PM

Quote:
 Originally Posted by Ceremony (Post 55695241) There's actually a surprising lack of X Files videos on youtube. Though when he pulls the kid out of the car he ends up at most 10 feet away, standing upright (not even off balance). The speed of him being pulled out is that fast you can't see it, he's in the car and in the next instant he's standing up.
In that case, the kid would probably die. He might even get ripped in half.

This kind of stuff happens a lot in movies. Example: in the Avengers, Scarlett Johansson gets a boosted jump from Cpt. America, and she grabs onto some kind of flying ship. In reality, her hand would probably just break when she tried to grab it. If she did somehow latch on succesfully, her arm would probably get dislocated and she'd fall to the ground.

 LadyStanley 11-11-2012 04:36 PM

Who ever said that Hollywood physics was survivable :sarcasm:

One reason why Mythbusters has such fun debunking movie scenes. :D

 xX Hot Fuss 11-12-2012 08:11 AM

Especially after just watching Felix plummet to the Earth, i would think the Human body is specifically NOT built to be moving that fast.

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