The Physics of Superheroes Everything I need to know about gravity I learned from... Superman? We talk with physics professor and comic book aficionado James Kakalios about his new book The Physics of Superheroes. How can the Fantastic Four make physics fun?
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The Physics of Superheroes

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The Physics of Superheroes

The Physics of Superheroes

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And for the rest of the hour, some comic relief--literally. Did you ever have debates among your comic book reading friends? Did you have them when you were a kid, as I did, about such problems as, `Hey, how could Superman leap tall buildings in a single bound?' or, `How fast do you have to be--how does he go faster than a speeding bullet?' and `How fast is a speeding bullet, and how fast do you have to go to beat it?' Or how about Spider-Man? How can he swing from a thread and, you know, not pull his arms out? Or what really killed his girlfriend, Gwen Stacy? Was it a deadly fall or the web that Spidey tried to save her with? Was that the cause of death? Well, my next guest has pondered these questions and a lot of other questions about the comic book superheroes. He's gathered his observations and some equations on the science found in some of our favorite comic books and collected them into a book of his own. Let me introduce him. James Kakalios is the author of "The Physics of Superheroes," coming out this month by Gotham Books. He's professor of physics and astronomy at the University of Minnesota in Minneapolis. He joins us today from Minnesota Public Radio in St. Paul.

Welcome to the program.

Dr. JAMES KAKALIOS (Author, "The Physics of Superheroes"): Thank you for having me.

FLATOW: I got to ask you first. Did you choose the publishing house Gotham Books?

Dr. KAKALIOS: No, it was a fortunate coincidence. They're a division of Penguin Press, and whenever I point that out, people say, `Ah, the penguins.'

FLATOW: I'm talking with James Kakalios, author of "The Physics of Superheroes" on TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

What made you decide as a physics teacher that this was the way to teach physics?

Dr. KAKALIOS: Well, I've been teaching introductory physics for years, and we always had examples involving masses forming from towers or shooting projectiles at an angle of 37 degrees from a cliff 200 meters above the ground. Quite frankly, in 20 years of being a physicist, I've never actually needed to know these results, but I tried to enliven the class, periodically over the years, by bringing in examples from movies or comic books. And physics seems so dry to many students that the standard complaint is always, `When am I ever going to use this in my real life?' And...

FLATOW: When am I doing an upstream/downsteam problem?

Dr. KAKALIOS: Right. But interestingly enough, whenever I use comic book examples, the students never wonder when they're going to use this in their real life. Apparently, they all have plans after graduation that involve Spandex and patrolling the city. And knowing as I do how many mad scientists there are out there, I think that's a good thing.

FLATOW: I'm also fascinated by the evolution of comic books that you talk about and the characters in them and how, for example, Superman...


FLATOW: ...he did first start out as able to leap tall buildings, but then he could fly at some period. What brings on these changes?

Dr. KAKALIOS: Probably--I don't know for sure. My guess would be money--that "Superman" was first published in 1938, created by Jerry Siegel and Joe Shuster, these teen-agers from Glenville, Ohio, and as you say, he originally was more of a science fiction type hero. He came from a planet with a much greater gravity than Earth, so he was able to leap great distances, lift large masses, nothing less than a bursting shell could penetrate his skin. But he wasn't, you know, invulnerable. He couldn't fly; he couldn't do these other things. And interestingly enough, back in the '30s, the first people that Superman went up against were sweatshop owners, crooked politicians and Washington lobbyists, and he gave vent to a lot of the frustration that a lot of readers during the Depression no doubt felt.

When he became the center of a multimillion-dollar licensing enterprise--movies, you know, shorts during the cinema, radio programs, toys--he started to fight Lex Luthor and Brainiac and characters who wanted to take over the world but leave the corporate power structure safely undisturbed, and as his supervillains got more and more powerful, he became more and more powerful, and eventually the origin of his powers was changed from coming with a planet with larger gravity to the yellow sun on Earth. Somehow the fact that our sun appears yellow to us, which is characterized by a wavelength of 570 nanometers, is profoundly different from the red sun of Krypton, with a wavelength of 650 nanometers.

FLATOW: And that's how you can teach these wavelengths is what...

Dr. KAKALIOS: You can--it's only 80 nanometers, but apparently it enables someone to bend steel in their bare hands.

FLATOW: Wow, I've gotta get some of that. 1 (800) 989-8255 is our number. If you would like to call--we've got about a minute till the break. You also--so how do you teach gravity using Superman? He's jumping up and down? You can teach about the different forces of gravity. Krypton in here and differences?

Dr. KAKALIOS: Well, it's a well-posed physics question. How fast would you have to be moving, coming up off the ground, in order to leap a tall building in a single bound? Let's say 650 feet, an eighth of a mile, which the comics specified as his leaping range. Well, the faster you go, the higher you'll jump. And you can calculate this, and it turns out you have to be going about 140 miles per hour, which is why I don't leap a tall building in a single bound and I'm lucky if I can leap a trash can in a single bound. So...

FLATOW: We're going to have to--hang on to that thought 'cause we, as they do in the comic books, have to tune into the next chapter when the next book comes out. So we have to take a break and we'll see you on the other side of the break and talk more with James Kakalios, author of "The Physics of Superheroes," talking your calls and finishing off how Superman is able to leap those tall buildings. So stay with us. We'll be right back after this short break.

I'm Ira Flatow. This is TALK OF THE NATION/SCIENCE FRIDAY from NPR News.


FLATOW: I'm Ira Flatow. You're listening to TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

We're talking with James Kakalios, author of "The Physics of Superheroes," that's published by Gotham Books. You can't forget that publisher name for "The Physics of Superheroes." And the book is going to be coming out next month. It's a great book. He talks about and explains all the science of not only Superman but of all the other superheroes you talk about. And before the break, James was talking to us about what it takes for Superman to be able to leap a tall building in a single bound.

Dr. KAKALIOS: Yes. So as you no doubt know, Superman is the last survivor of the doomed planet Krypton. His scientist father, Jor-El, sensing that the planet was about to explode, sent him off in a rocket ship to Earth. I have to say as a father I can empathize. Many's the time I wanted to put my own kids in a rocket ship and send them off to outer space. But he came to Earth and he has powers and abilities far beyond those of mortal men, presumably because his muscles and skeleton are adapted to a much heavier gravity. So just as if we go to the moon, we can leap over moon buildings and lift moon cars over our heads and amaze the moon people there, Superman is able to just do this here on Earth.

And in this class that I teach, a freshman seminar at the University of Minnesota, Everything I Need to Know About Science I Learned From Reading Comic Books, we ask how much force do your legs have to supply to the ground in order to enable you to leap a tall building in a single bound. And it's actually an excellent application of Newton's second law of motion: Force equals mass times acceleration. He needs to get a large acceleration as he presses down on the ground. And Newton's third law, that forces come in pairs, mean that the ground presses back up on him and enables him to leap up, up and away. And in order to leap, say, 650 feet, a 30- or 40-story building, his legs have to supply a force of about 6,000 pounds.


Dr. KAKALIOS: So--yeah, that's pretty buff. So presumably his legs are that strong because he has to be able to support his weight on Krypton, or at least his DNA encoded for his legs to be that strong. So that implies--if we assume that that is his greatest leap and is able to supply a force twice that of his normal standing weight on Krypton, then he weighs about 3,000 pounds on Krypton. We know he weighs roughly 220 pounds on Earth, so that implies that the minimum excess gravity of Krypton is 15 times that of Earth. So just by using the experimental fact that he can leap a tall building in a single bound, we can calculate what the gravity on Krypton must have been. Then Newton's law of gravitational attraction enables us to calculate how you would build a planet with that much gravity. And it turns out that you can do it, but the only way to get that excess gravity is if the Krypton had a neutron-star core. It needs an extra superdense mass, and thus you realize why Krypton exploded because...

(Soundbite of laughter)

FLATOW: So you have it full circle.

Dr. KAKALIOS: ...this neutron star material produces tremendous strain that at some--makes a stable distribution of matter tenuous at best, and at some point, earthquakes would set off and plate tectonics would alert an astute scientist that now's a good time to put your kid in a rocket ship and send him out into space.

FLATOW: There you go. 1 (800) 989-8255. James in New York. Hi, James.

JAMES (Caller): Hi. How are you?


JAMES: I would like to know how fast The Flash must run to run over water.

Dr. KAKALIOS: Excellent question. Turns out to be not as fast as you would think. What we do in the class is obviously superpowers, like running at superspeed are physically impossible, so we don't go through and try to prove that the superheroes are, you know, impossible because hopefully most of the students won't be surprised by this. But we grant each character...

JAMES: You mean you can't run that fast?

Dr. KAKALIOS: Oh, no, no, no. He--we grant--what we do is we grant each character a one-time miracle exemption. So we say, well, if you could run at superspeeds, like The Flash, could you run across the ocean? You know, could you catch bullets in midair and so on? Could you drag people behind you in your wake? And we say if you could run at superspeed, yes, you can do all of those things. If you can run faster than, say, a hundred miles an hour, then you're effectively acting like a Jet Ski and your feet are pressing down on the water so fast that the water doesn't have time to get out of the way and it forms a solidlike shock front underneath your foot that provides you with some footing to keep going.

FLATOW: There.

Dr. KAKALIOS: So if he's allowed to run--if you, you know, grant me that exemption from the laws of nature, then you can have him run across the ocean no problem.

FLATOW: There you have it. Now you got the ans...

JAMES: Thank you very much. I really appreciate that.

FLATOW: Thanks. Thank you, James.

Dr. KAKALIOS: You're welcome, James.

FLATOW: 1 (800) 989-8255. You've piqued our listeners' interest. Meg in Cincinnati. Hi, Meg.

MEG (Caller): Hi. How are you?

FLATOW: Fine. Go ahead.

MEG: Well, we hang on to SCIENCE FRIDAY. We work in a lab and my colleagues and I listen to this every Friday afternoon, and this has just got everybody talking here in the lab. We want to know how shoe heel-height would affect Wonder Woman's powers. Would she get more powerful the higher her boot heels, or would she actually lose physical strength with a higher heel?

Dr. KAKALIOS: Wonder Woman is one of those people who--her powers are more magical-based, and so I'm not quite sure how her boot heel would matter...

FLATOW: Yeah. Tell me, Meg, you guys are thinking too much about this.

(Soundbite of laughter)

Dr. KAKALIOS: No, no, no, no, no. That's OK.

FLATOW: Why did you come up with her heel height?

MEG: Well, it seems to me that when you're in a high heel, you don't have as much stability, you don't have as much strength.

FLATOW: Right.

MEG: You're constantly counter...

FLATOW: Oh, I see what you're saying. So where is the critical point that her heel height would make her lose some of her agility and powers and things?

MEG: Right.

FLATOW: She'd fall off her shoes, or something like that.

MEG: Exactly.


MEG: Or not just that. Just be so off-balance...

FLATOW: Right.

MEG: ...and her out of alignment and so forth that she couldn't grip quite as much.

FLATOW: But she has magical powers.

Dr. KAKALIOS: Or--well...

MEG: Well, she does have that lasso thing going, but she could also...

Dr. KAKALIOS: She has the Lasso of Truth. Interestingly, her creator, Charles Moulton Marston, I believe is his name--yes. Charles Moulton Marston invented the lie detector.

FLATOW: No kidding.

Dr. KAKALIOS: And so the psychologist who invented the lie detector then went on to create Wonder Woman and gave her a Lasso of Truth.

MEG: Oh.

FLATOW: See the things you learn on this program.

MEG: Really.

FLATOW: All right, Meg.

MEG: Well, thank you.

FLATOW: Hope you guys keep listening.

MEG: Oh, we always do. Thanks so much.

FLATOW: Thanks a lot. Bye-bye.

MEG: Bye-bye.

FLATOW: 1 (800) 989-8255 is our number. Let's go to Beth in Athens--stay in Ohio. Hi, Beth.

BETH (Caller): Hi.

FLATOW: Hi there.

BETH: I just wanted to comment--was it Mr. Kalitolis--I'm sorry--was your name?

Dr. KAKALIOS: Kakalios. Don't worry about it. Technically...

BETH: I'm sorry. I apologize.

Dr. KAKALIOS: ...I mispronounce it myself, so...


FLATOW: Mr. K in class.

Dr. KAKALIOS: Yes, that's right. Dr. K. The K stands...


BETH: Dr. K.

Dr. KAKALIOS: The K stands for action.

BETH: OK. Need a superhero outfit. Well, I'm just like really excited to hear that you made this book because I know when I was in high school physics wasn't that fun. But I had a wonderful teacher, Mr. Mangold(ph), and he actually had us learn--like I remember an example that was really interesting. He made us calculate the velocity of the speed that Chevy Chase was going on his sled in that one Christmas movie. I'm sorry I can't remember it. But he would just give great examples and it helped the class out to learn and actually have fun with learning physics--physics and calculus. So it was just amazing, and I just wanted to say thank you. That's great.

FLATOW: Oh, thanks for your call.

Dr. KAKALIOS: Thank you. Yes, the students really seem to respond to--once you get outside of the somewhat artificial examples. Even if you're doing things that are clearly unphysical--superheroes or movies--they realize that if you can apply the laws of physics there, well, then maybe they actually would work in the real world.

FLATOW: Yeah. There's--one of my favorite examples you used in your book and that's when Gwen Stacy, Spider-Man's girlfriend, dies in The Amazing Spider-Man number 121...


FLATOW: But there's controversy about what act actually killed her there.

Dr. KAKALIOS: Right.

FLATOW: Tell us about that.

Dr. KAKALIOS: Well, Spider-Man was fighting the Green Goblin, who at one point kidnapped Gwen Stacy, Spider-Man's girlfriend, and brought her to the top of the George Washington Bridge in order to lure Spider-Man into battle. At one point during the fight, she gets knocked off the bridge and falls to her apparent doom. Spidey shoots his web after her and stops her in the nick of time, but as he brings her back up to the top of the bridge, he discovers to his horror that she's in fact dead. And this has been a controversy among comic book fans for a long time. The Green Goblin said, you know, `Romantic idiot. You know, she was dead before your web even reached her. A fall from that height would kill anyone before they hit the ground,' which if this is true, the implications for skydivers and parachutists suggest a massive conspiracy of silence from the part of the aviation industry.

But nevertheless, comic book fans have long argued whether it was the webbing or the fall that killed Gwen Stacy, and we analyzed this in our class. We say if you fall 300 feet from the top of a bridge, how fast are you going after falling 300 feet? You're going nearly 95 miles per hour. In order to stop in, say, half a second, how much force has to be applied? The faster you're going, the greater the momentum, and the shorter the time the greater the force needed to stop you. So if you go from 95 miles per hour to zero in half a second, it takes nearly 10 G's, 10 times the acceleration due to gravity. So it's not unreasonable that her neck would break, and in fact, in the comic book there's a little snap sound effect that's drawn by her neck that shows the consequences of this.

And then in the class we point out that this is how air bags save lives. In the past, if you're driving 60 miles an hour and you hit something, well, you kept going because an object in motion remains in motion until acted upon by an outside force.

FLATOW: ...(Unintelligible).

Dr. KAKALIOS: That's right. And the outside force used to be supplied by the steering column or the windshield, which the time of contact is very brief so the force was very high. Air bags do two things. They spread the force over a larger area, and they deform under contact. So the time to slow you down in increased, and if the time goes up the force can go down, so it knocks you out but you're still alive. So the same principle that unfortunately killed Gwen Stacy is operating in air bags in our automobiles.

FLATOW: So he killed her then.

Dr. KAKALIOS: Well...

FLATOW: By his trying to save her. Did he learn anything trying to--you point out he learned from his lesson in saving someone else falling.

Dr. KAKALIOS: Absolutely. There's--a couple of years ago there was a Spider-Man story where he's needing to stop a windshield washer who's falling down the side of an office building, and his thought balloon shows that he's actually working through the problem. `I can't just grab him,' or, `Changes in momentum will rip his arm off,' and so what he does is he tries to match his velocity to that of the windshield washer, grabs him, then shoots his webbing and since Spider-Man has spider strength, part of his miracle exemption, he can absorb this greater force without undue harm. So Spider-Man has learned. Apparently, even the Green Goblin has learned.

There was an article about this controversy in Wizard magazine and I wrote a letter pointing out that in our class we'd solved this and showed that it wasn't due to the webbing. And a little while later, the Green Goblin is taunting Spider-Man and he's pointing out that it was the webbing that killed her, not the fall. So it may have taken them 30 years, but the Goblin has now learned conservation momentum. And I don't know how well I do within my class, but if I can teach a homicidal maniac like the Green Goblin about physics, well, maybe I'm doing OK.

FLATOW: Yeah. 1 (800) 989-8255 is our number. We're talking about "The Physics of Superheroes" and the name of that book, which is "The Physics of Superheroes," with James Kakalios, professor in physics and astronomy, University of Minnesota. And the book should be on store shelves by September 26th, so...

Dr. KAKALIOS: Twenty-ninth.

FLATOW: September 29th.

Dr. KAKALIOS: September 29th, right.

FLATOW: And we're talking about it on TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

Well, if the reaction is anything from what we're getting from our listeners, it should be a great hit, you know?

Dr. KAKALIOS: It's trying to explain in hopefully a fun and accessible manner the key concepts of physics.


Dr. KAKALIOS: Everything from Isaac Newton to the transistor with not an incline plane or pulley in sight.


Dr. KAKALIOS: All the examples come from superhero comics.

FLATOW: Sarah in Nashville. Hi. Welcome to SCIENCE FRIDAY.

SARAH (Caller): Hi, Ira. It's really nice to talk to you. I love the show.

FLATOW: Thank you.

SARAH: I actually wrote--I am a graduate of the University of Minnesota, and had Dr. Kakalios for Intro to Physics. I was--and it was a great...

Dr. KAKALIOS: Uh-oh.

SARAH: No, I loved it. It was...

Dr. KAKALIOS: Thank you.

SARAH: I was one of those kind of nerdy science students, though, who knew I really liked science and didn't realize till I took your class that I kind of liked comic books too. So I just wanted to thank you for that, and I am sort of saddened here that I--I've always wanted a Wonder Woman Lasso of Truth. Is it possible that you'll ever be able to come out something like that?

Dr. KAKALIOS: Mmm...

FLATOW: Maybe in the Toys "R" Us version. You never...

Dr. KAKALIOS: Yeah. Well, there's some things that the Pentagon's working on. We're not allowed to talk about it.

SARAH: Oh, I understand.

FLATOW: All right, Sarah. Thanks for calling.

SARAH: Thank you.

FLATOW: You're welcome.

Dr. KAKALIOS: Thank you very much.

FLATOW: Is there one concept that's very hard to teach, that really lends itself well, or something that's so hard that even the comic books can't, you know, cover it? I'm thinking specifically maybe of the concept of time--you know, time and warped space or something like that.

Dr. KAKALIOS: Well, there are some really good time travel stories through out comic books. Interestingly enough, back in the 1960s Superman went back in time and fixed all sorts of events in history. He saved Lincoln from being assassinated. He saved the--General Custer at Big Horn. And when he got back to his regular time, he discovered that all the events were not recorded in the history books and discovered that what he had actually done when he went back in time is visit a parallel earth and parallel universe. These concepts that if you go back in time you make a transition through the many worlds interpretation of quantum mechanics are only now in 2001, 2005 being applied in theories of quantum gravity. So it's a beautiful illustration of modern concepts being applied in string theory back in the 1961 Superman story.

FLATOW: And you say it's another example of the comic books being ahead of the physics curve.

Dr. KAKALIOS: That's right.

FLATOW: Can you talk about anything more complicated than that--you know, just touching on string theory, or is that basically where it is?

Dr. KAKALIOS: Well, let's--I mean, we talk about--in the book I get all the way up through quantum mechanics...

FLATOW: Right.

Dr. KAKALIOS: ...using the many-worlds interpretation. We talk about solid-state physics in iron-man transitorized armor; how the same principles whereby certain semiconductors are photoconductors and we talk about solid-state physics and related to The Invisible Woman and talk about how she might possibly turn invisible by changing her band gap, and we talk about that, and that might also explain why she doesn't become blind when she turns invisible.

FLATOW: Do the students react equally? Men and women in class? Or do they get as much fun out of it as, you know...

Dr. KAKALIOS: Yeah. I try to, at least, and it does seem to...

FLATOW: Yeah. Yeah.

Dr. KAKALIOS: ...I mean, you can see from your callers. We had Beth and Sarah and Meg.

FLATOW: It's true, I've had more women on the screen than men. And I've gotta stop it there. We want to thank you very much for taking time to talk with us, and good luck on your book, "The Physics of Superheroes" by James Kakalios.

Dr. KAKALIOS: Thank you very much.

FLATOW: Coming up September 29th. Have a good weekend.


FLATOW: Surf over to our Web site at You can also download a podcast if you missed any of today's or back editions of SCIENCE FRIDAY. They're there to take with you. Also, SCIENCE FRIDAY's Kids' Connection; we'll have some interesting stuff for the Kids' Connection this week.

Have a great weekend. We'll see you next week. I'm Ira Flatow in New York.

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