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  • Diandra Leslie-Pelecky: I thought that was really creative

  • and totally possible.

  • My name is Diandra Leslie-Pelecky.

  • I have a PhD in physics, and I started off my life

  • as a condensed-matter physicist working in nanomedicine.

  • Along the way, I ended up writing a book called

  • "The Physics of NASCAR."

  • So today I'm gonna use that knowledge

  • to talk to you about some clips

  • from "Fast and Furious."

  • This is one that is a little difficult to analyze,

  • because you're not quite sure how long they're falling.

  • It could be anywhere from 11 seconds to maybe 15 seconds.

  • That's a really long time to fall.

  • I calculated out

  • what Dom's terminal velocity would be,

  • and that's biggest velocity you can fall

  • given that drag gets bigger as the speed goes up.

  • And he almost approaches it.

  • After 11 seconds,

  • Dom would be going 124 miles per hour

  • when he hit the water.

  • He would have fallen about 1,775 feet

  • at that point.

  • Now, 124 miles per hour into water,

  • maybe that's survivable.

  • Laso Schaller holds the record for the highest jump.

  • That was from 193 feet.

  • He hit the water at 76 miles an hour.

  • He broke his right clavicle and dislocated his pelvis.

  • The Golden Gate Bridge is about 245 feet.

  • People hit the water at 86 miles an hour.

  • Only 5% of the people who jump survive.

  • So the probability of them surviving is pretty small.

  • They built a launcher and took this beautiful

  • 1966 Corvette and actually launched it

  • off the side of the cliff,

  • and then they had stuntmen

  • who did it separately from the car

  • because being hit by a car midair

  • would be worse than actually hitting the water.

  • And so they had the stuntmen do it,

  • but the stuntmen were on cables.

  • Then they came back, did it on a green screen

  • with the actual actors, who were, you know,

  • maybe eight feet above the ground.

  • But this one I think I would have to give a score

  • of two, because there's absolutely no way

  • they could've survived a jump that long.

  • So, this a 1969 Camaro.

  • It's got a mass of about 3,500 pounds.

  • So, they're hitting 90, so you know

  • the boat's going at least 90 miles an hour.

  • One of the things that you notice is that

  • when the car and the boat are both speeding along,

  • they're parallel to each other.

  • Now, how they all of a sudden get behind the boat,

  • I'm not actually sure how that happens.

  • But let's assume they can do that.

  • When they take off, they're going at approximately

  • 45-degree angle off this ramp,

  • and they're going 120 miles an hour.

  • So not all of the speed

  • is taking them in a horizontal direction.

  • So I've taken cosine of 45; they're only now going

  • about 78 miles per hour toward the boat.

  • Now, that's a problem,

  • because the boat and the car looked like

  • they were going the same speed.

  • And the problem is, if the boat's going 100 miles per hour,

  • it'll be 1,200 feet from the shore.

  • The problem is, the car can only go 945 feet

  • in the time it's in the air.

  • There's actually no way

  • that the car could make it onto the boat.

  • Let's pretend the boat is only going 78 miles an hour,

  • because if they are, it's totally possible.

  • It is going fast enough, and it makes up

  • all the distance between it and the boat.

  • So if you include drag,

  • they're gonna lose some of their speed

  • due to air resistance.

  • They're still gonna hit that boat

  • at around 105 miles per hour.

  • The kinetic energy of the car

  • and the guys in the car, at that point,

  • is equal to about a fifth of a pound of TNT.

  • Some of that goes into wrecking the boat

  • and wrecking the car, but not all of it.

  • Which means some of it is gonna go into the guys,

  • and they're gonna have a whole lot worse

  • than a broken arm.

  • I think I'd give it probably a seven out of 10,

  • because it's possible it could happen.

  • They had to modify this tank

  • so it could go 60 miles an hour,

  • 'cause they normally only go 30 miles an hour.

  • Dom, we'll assume his car was going 60 miles an hour,

  • so when he left it, he was going 60 miles an hour.

  • So you can look at conservation of momentum

  • and figure out that by the time they hit and continued on,

  • they were probably going around 40 miles an hour.

  • So a little bit of change in speed,

  • but the problem is when he hit the car

  • going 40 miles an hour, and she is about 120 pounds,

  • he's about 225, so you're talking about 340 or so pounds.

  • You're gonna be hitting it with an acceleration

  • of almost 100 g.

  • They have no protective gear.

  • So, you know, race-car drivers

  • routinely survive hits of 100 g.

  • They've got a big car around them.

  • And maybe it's possible that Dom could launch himself

  • at just the right angle to intercept Letty.

  • And then maybe it's possible that

  • that path took you onto the second bridge

  • instead of over the first one,

  • and maybe it's possible that there happened to be a car

  • at the point where they were landing,

  • and maybe it's possible

  • they survived hitting the car together.

  • Each one of those things might have happened,

  • but all four of them together

  • is just too much of a coincidence.

  • Once you're in the air, you cannot steer.

  • So if you misjudge in any way,

  • you're gonna miss her.

  • Now, if you watch baseball players,

  • they develop this very intuitive ability

  • to know the arc of a ball.

  • And after all, it's just a parabolic motion.

  • Maybe just Dom understands physics so well

  • that he knew exactly where to launch himself.

  • And if you talk to a race-car driver,

  • they would be able to understand centripetal acceleration

  • and explain it to you. Again, no equations,

  • but they get this intuitive understanding for it.

  • So, it's just possible, maybe Dom has

  • rescued enough people who are flying through the air

  • that he understands how to do it.

  • Hollywood has its own physics.

  • One of the rules is they have time dilation,

  • which is that when something really exciting is happening,

  • it can take as long as you want it to take.

  • Slowing down, let's say 120 miles an hour,

  • and I pick that number only because

  • that'll tell you, at 120 miles an hour,

  • the car is going two miles every minute.

  • So for every minute of that clip,

  • you're traveling two miles.

  • The longest airport runway in the word is 3.4 miles,

  • which means if they were on that runway,

  • this still could take 1.7 minutes.

  • And it doesn't.

  • It takes a lot, it takes, like, 11 or 12 minutes,

  • which would result in just this unfathomably long runway.

  • OK, so Dom is driving a 2012 Dodge Charger,

  • and let's pretend this is a super-reinforced version

  • of a Dodge Charger.

  • He doesn't have a lot of time to get up speed.

  • Because he's only got the inside of a plane,

  • and as you saw from the fight that was going on,

  • there's not a lot of room.

  • I think I have to give a one.

  • Just because here,

  • they stretched my ability to ignore reality

  • just a little further than I'm capable of doing.

  • Try to figure out how much that vault weighs,

  • according to the storyline.

  • So, we're gonna assume it's a 5-ton vault.

  • That's about 10,000 pounds.

  • There's $100 million in $100 bills.

  • That's gonna give us another 2,200 pounds.

  • Dom is 225 pounds,

  • and the car is 4,180 pounds.

  • That gives us a total weight of 16,605 pounds

  • that his car has to accelerate.

  • If you ever tried to move something heavy,

  • like a refrigerator or a bookcase,

  • you push on it, and it doesn't move.

  • And you push harder, it doesn't move.

  • And you push harder, and finally it moves.

  • That moment when it moves,

  • you've just overcome the static frictional force.

  • The static frictional force is higher

  • than the kinetic frictional force.

  • And what that means in real-people talk

  • is that once you get something moving,

  • it's much easier to keep it moving.

  • So the question is,

  • is it possible for this 2010 Charger SRT

  • to overcome the friction needed to move?

  • So we're gonna calculate how long it would take him

  • to accelerate up to 50 miles an hour.

  • We've got the 425-horsepower car

  • accelerating 16,605 pounds.

  • And it turns out that would take about 5.86 seconds,

  • which is a little longer than it took him

  • to actually do it in the movie.

  • So the fact that he got the car accelerating that fast,

  • that definitely couldn't happen in real life.

  • But that's without friction.

  • So once you put friction in,

  • what you find if you calculate

  • is that the coefficient of friction between, like,

  • steel and asphalt is pretty high.

  • And you probably could not,

  • even with a nitrous oxide boost,

  • get the vault moving.

  • So, once you got it moving, you could keep it moving.

  • What the folks have said who did this stunt,

  • they found the same thing.

  • They learned a lot about static friction the hard way.

  • And they actually put a slippery material

  • on the bottom of the vault to get it moving.

  • But one of the problems with that

  • is when you make something easier to start moving,

  • you also make it easier to stop moving.

  • And my understanding is they were very surprised

  • when they thought it would come to a stop

  • and it took a lot longer to stop than they thought it would.

  • The other thing is the question of,

  • you have this fairly small mass of a car and Dom.

  • That's about 2,000 pounds.

  • And the mass of the vault,

  • which is about 15,000 pounds.

  • So you've got something that's seven times bigger

  • than something else.

  • Now, think about when they're coming down

  • and then Dom starts, stops, and he lets the vault

  • sort of swing around.

  • The vault is, you know, seven times heavier

  • than Dom and his car.

  • And I just don't buy that he has enough traction

  • to swing the vault without the vault pulling his car along.

  • Making these stunts work in real life,

  • with practical effects and not CGI,

  • so they built something like seven or eight different vaults

  • with different weights so that they could do

  • all the different parts with the vault.

  • And in fact, in some points, they actually had

  • a little semi cab inside the vault

  • and the vault was driving around by itself.

  • So I would give this stunt a five.

  • I mean, we've all tried to go up a down escalator, right?

  • That's all he's doing there.

  • This whole stunt relies on

  • the person being able to run faster

  • than the bus is falling.

  • When they filmed this, the stuntperson did actually

  • run up the bus as it was falling.

  • I had some real questions, because

  • it's not like you're pushing off something solid.

  • You're pushing off something that's moving

  • in the other direction.

  • It spun around to be in exactly the right position

  • for him to grab the bar.

  • When he's holding the bar and she stops suddenly,

  • you get this really great example of

  • Newton's law of motion

  • where an object in motion will keep moving,

  • because she stops the car, and he keeps going flying around.

  • I would give this one a 10 for running up the bus.

  • I thought that was really creative and totally possible.

  • Again, you see a lot of tight shots,

  • so it does make it hard to see

  • what's going on necessarily.

  • This is a Lykan hypercar,

  • and it's got 780 horsepower.

  • This car is $3.4 million.

  • There's only seven of them in the world.

  • Sometimes I think they put it in slow motion

  • just so people like me

  • can't do the detailed calculations and mess with them.

  • How fast do you have to be going

  • so that you can span the distance between the buildings?

  • So, if we assume that distance is 150 feet,

  • you're gonna fall a little bit.

  • So anytime something comes off horizontally,

  • it's going to go down a little bit.

  • And you can actually see it in there,

  • that it probably falls about two stories,

  • which is roughly 20 feet.

  • And so the question is,

  • how fast do you have to be going to fall two stories

  • in 150 feet of horizontal distance?

  • If you're gonna fall two floors,

  • it would take just a little more than a second,

  • and you'd need to be going 137 miles per hour.

  • If you fall four floors, it would be about 1.6 seconds,

  • and you'd have to be going only 95 miles per hour.

  • Now, this car has a top speed of 245 miles per hour.

  • Top speed is no problem.

  • What is a problem, however,

  • is how long it takes you to get to top speed.

  • So, the car goes 0 to 60 miles an hour in 2.8 seconds.

  • In order to do that, it needs 123 feet

  • if you assume constant acceleration.

  • Those look like pretty small spaces,

  • because he was doing an awful lot of turning

  • as he was going around.

  • And that's only 60 miles an hour.

  • If you wanted to get to 125 miles an hour,

  • according to the specs,

  • that would take you 9.4 seconds.

  • You would need 861 feet to reach that speed,

  • and I don't see how you'd do that

  • in that tiny little tower.

  • And the other problem is that

  • when they're just driving around,

  • they must be pulling tremendous g-forces,

  • because they're driving these tiny little circles.

  • I tried to look up the coefficient of friction

  • between tires and marble, but it turns out

  • that it's very hard to find because most people

  • do not drive cars in their apartment buildings.

  • So I couldn't find that, but even so,

  • you know, I question, at going at high speed on marble,

  • whether he could even keep traction going around like that.

  • You know, again, you've got another example of,

  • there's a bunch of things that could happen,

  • and if you put them all together, you might not buy it.

  • Even the very strong, reinforced glass

  • they would use on a skyscraper like this

  • is not gonna stand up to a car that's 3,000 pounds

  • traveling at 120, 130 miles per hour.

  • The kinetic energy of the car is just too high.

  • Was he not wearing a seatbelt the whole time?

  • I just love the look after he does these things.

  • I mean, he just sort of looks like, "Oh."

  • I understand this Charger was especially modified

  • so it could drive on ice.

  • Obviously, the ice here is gonna be pretty thick,

  • but if you've got that much heat,

  • it's gonna melt the ice,

  • and that's gonna make it much harder to get traction.

  • The physics of how the car would move after he hit it,

  • that was pretty accurate.

  • I was pretty impressed by that.

  • One of the things that happens

  • that people don't appreciate

  • is when a car is on fire,

  • the fire quickly depletes all the oxygen.

  • And, you know, it's using it up,

  • and if you're in a car, you get very, very warm,

  • you get disoriented, there's smoke,

  • you can't see what you're doing.

  • And so I think, when something's on fire,

  • him coming out of this amount of fire,

  • that's got some issues with the realism, too.

  • I don't see any reason why this couldn't happen.

  • So this one I would have to give a 10.

  • I think this one's pretty plausible.

  • So, if you look up a fuel tanker that holds,

  • oh, I don't know, maybe 7,000 gallons of gasoline,

  • the density of gasoline is 6.073 pounds per gallon,

  • about 42,000 pounds coming toward them.

  • Now, if it were something doing, you know,

  • moving regularly, something bouncing,

  • that'd be fine because you could gauge it.

  • It's like a jump rope, where you know it's coming around,

  • you know to jump.

  • But the problem with this

  • is if you look how it's rolling,

  • it's rolling in this direction and it's rolling forward.

  • So there's no way you can predict

  • exactly how it's going to roll.

  • And if the tanker is 42,000 pounds

  • and the car is 4,000 pounds,

  • it's gonna squish the car.

  • So, my first car was a 1988 Buick LeSabre,

  • which is about the same size

  • as the 1987 Buick Grand National that you see.

  • The chances of it rolling over the tanker,

  • pretty darn slow.

  • When the tanker starts rolling,

  • it's got a certain amount of kinetic energy,

  • but every time it hits something,

  • like the wall of the canyon or the ground,

  • it's gonna lose some of that kinetic energy.

  • And that means it's not gonna bounce as high.

  • So actually the longer he waits,

  • the harder it is gonna be for him

  • to get his car under that tanker.

  • So I would give that one a three.

  • So, this a Nissan 350Z, I believe.

  • The person inside the car is actually using

  • a combination of the steering wheel,

  • the clutch, and the brakes

  • to make the car go around the turn.

  • And it turns out it's actually easier

  • to drift around the turn

  • than it is to drift in a straight direction.

  • I believe that this guy could probably do that,

  • but I'd like to know how many takes it took.

  • But you can drift for as long as your tires will hold out.

  • It's a problem because you want to have

  • equal traction on all four wheels.

  • And that means you need the same amount of weight.

  • When drifting, what you want is

  • you want the rear end of the car

  • to be able to slide back and forth.

  • When you're actually driving where the tires are rolling,

  • you're actually sliding those tires.

  • And so it's a totally different phenomenon.

  • At some point, you're going to do enough damage to them

  • that they're probably going to pop.

  • A good driver can definitely do that.

  • Now, if they would've shown the other guy,

  • who's just learning, doing that,

  • I would've given it a zero.

  • This is a perfect example of a static equilibrium.

  • So, as long as all the cars

  • are pulling with the same force,

  • Dom can't go anywhere.

  • And what that means is,

  • imagine it's just Dom and two cars,

  • one pulling left, one pulling right.

  • Those two cars are pulling with equal force.

  • Dom can't do anything.

  • The problem you have is

  • the traction between the tires and the ground

  • is what is our limiting factor here.

  • And they're talking about

  • his car having 2,000 horsepower,

  • 3,000 horsepower, 5,000 horsepower.

  • I don't know if it has that much.

  • All it has to have

  • is enough horsepower to get a little bit of slack.

  • What he's doing, is all he has to do

  • is get enough slack that he can move forward,

  • but what I'm not understanding here is

  • what's happening to the forces on him from behind.

  • And, of course, once he gets one of them,

  • then you've got unbalanced force.

  • And the only reason this works

  • is because the net sum of all the forces on this car

  • is gonna be zero.

  • And once he breaks free of one, all hell breaks loose.

  • This only works if the people on the other side

  • aren't doing their job right.

  • We have a theory that one of the people in the other cars

  • momentarily lost concentration

  • and that must be how he got out of it.

  • Because that's all we could figure out

  • how to make it happen.

  • And the problem giving something like this a grade

  • is that you don't get to see all of it,

  • because you're seeing the insides of each of the cars,

  • and you're not seeing the overhead view.

  • It's really hard to see how that happened.

  • The doctor has to have taken that into account,

  • because the purpose of the cast is to immobilize the arm,

  • and you have to take into account

  • the fact that he could flex his arm, so.

  • Could flexing the arm break the plaster of paris?

  • I bet it could.

  • But wouldn't you assume, I mean,

  • maybe that's why he's always wearing sleeveless clothing.

  • You know, it's hard to extrapolate,

  • because I know I couldn't do that.

  • So you watch some of those things,

  • and you go, "Yeah, he might be able to do that."

  • They aren't exactly 100% true to life.

  • I love these movies. I think they're fun to watch.

  • And I think it's really great to watch something

  • knowing the good guys are gonna win in the end.

Diandra Leslie-Pelecky: I thought that was really creative

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物理学家对11部《速度与激情》电影特技进行评分(Physicist Rates 11 'Fast And Furious' Movie Stunts | How Real Is It?)

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    joey joey 發佈於 2021 年 05 月 26 日
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