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Apollo 13 and bad physics

  1. Aug 13, 2006 #1
    Apollo 13 and "bad" physics

    Hey everyone. I'm new to this site becasue i thought you guys might be able to help me out with something.

    For a report, i am to find two "good" uses of physics and two "bad" uses of physics in apollo 13 and to explain why they are good or bad uses, using conceptual and mathematical aspects.

    I'm set with the "good" physics of Apollo 13. But i'm having some trouble with the "bad".

    I don't think there is any "bad" physics in apollo 13 becasue it was based on a true story, and the physics is correct in the movie, as it was in real life. Unless i am mistaken. How was physics used inapropriately in Apollo 13, as in the misuse of physics or violations in the law of physics? Apollo 13 is based on a true story. The only thing wrong about making of Apollo 13 is that it wasnt actually filmed in outerspace. But that has nothing to do with physics, thats just the directors choice.

    Can someone please help me out! Thank you!

  2. jcsd
  3. Aug 13, 2006 #2

    Chi Meson

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    You got a difficult movie for finding "Bad Physics." Apollo 13 is considered to be one of the movies that got it mostly right. I haven't seen it in a while, but I do remember a textual mistake at the point where the technician says something like "And it has to do all that by using less energy than that (pointing at a Mr.Coffee coffee maker--which I'm pretty sure wasn't even available then)."

    He either misused the word "power" or "energy, " but I'm not certain about that.
  4. Aug 13, 2006 #3
    In that scene, one technician says "So how much power do we have to deal with" and the other technician says "Barely enough to run this coffee pot for 9 hours".

    The spacecraft had to use less than 20amps of power to use for re-entry. Do you mean that a coffee pot can't run off of 20amps of power, and that how the word was misused?
  5. Aug 13, 2006 #4

    Andrew Mason

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    The mistake is the use of the word 'power'. The spaceship had stored energy not stored power. Power would be the rate of use of that energy. I have a feeling, however, that it is more true to life for the astronauts to have used power that way.

    You have to multiply current by voltage to get power. A coffee pot might have used 20 amps - it depends on the voltage. At 120 volts, it would use much less than 20 amps.

    I agree with Chi Meson that Apollo 13 is a pretty accurate movie from the physics perspective. Easy to find good physics but pretty hard to find the bad. The author of the book on which the movie was based, Jeff Kluger, who was also was a consultant on the movie, is a science writer.

  6. Aug 13, 2006 #5

    Chi Meson

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    As AM said, the mistake is in using the word "power" instead of "energy." But even engineers and scientists will often revert to "common use" (as opposed to "precise scientific use") in conversation, so it is a nit-pickey thing.

    He should have said either:
    "How much pawer do we have to deal with?"
    "Barely enough to run this coffee pot."


    "How much energy do we have to deal with?"
    "Barely enough to run this coffe pot for 9 hours."
  7. Aug 14, 2006 #6


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    Okay, so with the correct spin, the power thing is the first of the two examples. The second will be hard to find, but maybe watch all of the scenes carefully where zero gravity is depicted. That's a really hard thing to do correctly, even when a movie production crew is trying its best. Find a couple scenes where there are small zero-g mistakes. They probably won't be real obvious mistakes, but I'd bet that there are some small motion errors in some of the scenes.
  8. Aug 14, 2006 #7


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    In zero g, remember conservation of momentum! If someone pushes off the spacecraft, it should shift relative to everyone else!

    (Ok, that would probably not get you credit, but it's true)
  9. Aug 16, 2006 #8
    Thats an interesting point. when astronauts move around inside the capsule, how come the capsule doesnt move off course?
  10. Aug 16, 2006 #9


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    The center of mass of the capsule + astronauts stays on the same course. Conservation of linear momentum.
  11. Aug 21, 2006 #10
    Here are a few (not really what you're looking for, but errors nonetheless), but there are a few things that could be qualified as physics goofs.


    Goofs for
    Apollo 13 (1995)

    * Incorrectly regarded as goofs: The film contains an explicit notice that "certain characters and events have been fictionalized for dramatic purposes", so these changes are not goofs. For instance, the Lovells did not host a party during the Apollo 11 landing; Ken Mattingly was already at Mission Control when the Apollo 13 accident happened, and was not really the person who devised the power-up procedure. There are various other minute contradictions of history and the film is prey to a large number of factual errors due to the large volume of documentary footage/evidence from the actual event. This is not a documentary.

    * Factual errors: After the party, Lovell holds his thumb in front the gibbous moon. Then, telling Marilyn where to find "her" mountain, he says the Sea of Tranquility is "where the shadow crosses the white part." The terminator was in fact near the Sea of Tranquility on July 20, 1969, but the moon was less than half full; it's depicted in the scene as gibbous, with the terminator on the other side.

    * Factual errors: When Jim Lovell is standing in his garden looking at the moon (one eye closed) he covers and uncovers the moon (from his perspective) with his thumb. Since the moon was the only light source in this situation, the shadow of his thumb would have to be shading his eye. But the third person perspective shows the thumb's shadow elsewhere.

    * Crew or equipment visible: When Lovell is looking out the window and sees the oxygen escaping, a hand is visible in the bottom left corner of the window.

    * Factual errors: The seas are the dark parts.

    * Factual errors: In Houston the moon set that night at about midnight CDT, while the Apollo 11 astronauts were returning to their Lunar Module; hence it would not be visible after the party at the Lovells'.

    * Anachronisms: NASA's "worm" logo was not developed until 1975.

    * Anachronisms: A technician is wearing a Rockwell International logo on his coveralls. North American Rockwell became Rockwell International only in 1973 when they acquired Collins Radio.

    * Factual errors: The launch tower was on the north side of the Saturn V. If Mattingly was watching from east of the pad near the beach, then he would see it on the right.

    * Revealing mistakes: The downward view toward the rocket rising from the pad shows cars in the parking lots. During an actual launch, the pad was completely evacuated and the lots would have been empty.

    * Continuity: Houston confirms that the BPC (Boost Protective Cover) is cleared before it is jettisoned by Lovell.

    * Anachronisms: In April 1970, Lovell's daughter can be seen holding the Beatles' "Let it Be" album, which wasn't released until May 1970.

    * Continuity: When Apollo 13 is due for re-entry we briefly see Gene Krantz with a fastened collar and tie. A minute or so later he is seen fastening his collar and tightening his loose tie.

    * Continuity: At the beginning of the movie, Jim Lovell comes home with some champagne and greets Jack Sweigert and his date for the evening, Tracy. When Jack starts telling Tracy about some of the things Jim's done, she says, "Wow," with her hands clasped up by her chest. In the next shot, her hands are clasped down by her waist.

    * Continuity: Just after the explosion, when Lovell is saying "we've got multiple caution and warnings, Houston," the MET clock (Mission Elapsed Time in hours, minutes, and seconds) is plainly visible reading 091:34:10. When next seen less than a minute later, it has backed up to 056:55:12.

    * Factual errors: The actual explosion took place at MET (Mission Elapsed Time) 055:54:53, a full hour before the time shown.

    * Factual errors: The astronauts are shown looking at Mare Tranquilitatis, then crossing from sunlight into shadow, followed by loss of signal, all within seconds. In fact at loss of signal they had been in the moon's shadow for some time and were nowhere near Mare Tranquilitatis.

    * Factual errors: While passing over Tsiolkovsky crater on the moon's far side, the astronauts also speak of sighting Fra Mauro and Mare Imbrium, both nearly halfway around the moon.

    * Factual errors: Just after acquisition of signal, Houston tells the astronauts that their speed is "approximately 7,062 feet per second" and their altitude above the moon is 56 nautical miles. That speed is 500 ft/s below lunar escape velocity at that altitude, hence impossible on a free return trajectory. In fact, any free return trajectory symmetrical about the moon-earth line would put them at over 100 nautical miles altitude at acquisition of signal.

    * Factual errors: A TV scene at Mission Control shows Houston Astros player Jimmy Wynn hitting a home run on 13 April 1970. The Astros were shut out by the Los Angeles Dodgers 2-0 that day. The home run shown was hit 10 June 1967, in a game between Cincinnati and Houston, it was the longest in Crosley field history

    * Errors made by characters (possibly deliberate errors by the filmmakers): As Neil Armstrong walks on the moon, Walter Cronkite says the Apollo 11 landing is 18 months after the tragic Apollo 1 launchpad fire. It was actually 30 months after.

    * Anachronisms: "Mr. Coffee"-type drip pots weren't in use at the time.

    * Continuity: A red ashtray and a paper cup in the control center disappear between shots.

    * Anachronisms: The television that Blanch Lovell watches the final splashdown on is a Sharp model that was not made until the late 1980s.

    * Anachronisms: In the opening sequence with Apollo 1, the crew uses a black keyboard (Block II). The keyboard on Apollo 1 was white (Block I).

    * Continuity: During the re-entry simulation with Swigert, Fred Haise communicates with Houston after they confirmed radio blackout.

    * Factual errors: In some cold scenes in the LEM, breath is visible. The warm breath rises, which wouldn't happen in a weightless environment.

    * Continuity: When Mattingly goes to bed and takes the phone off the hook, the position of the receiver is different when he is woken up.

    * Crew or equipment visible: A bearded crew member is visible in the lower right corner of the screen towards the end of the movie, about the time Jack jettisons the service module.

    * Continuity: Before Gene Kranz calls for people to "Listen Up People" in mission control, we see Deke Slayton move from the back row to CAP COM row 3 times.

    * Audio/visual unsynchronized: News reporters outside of Lovell's home during landing voices are out of synch with the video (observed on the IMAX version.

    * Revealing mistakes: When the astronauts are standing in the moving elevator, the reflection in their helmets is of the stationary elevator.

    * Continuity: At the end of the film, Gene Kranz sits down in his chair and puts his hand to his head. A few seconds later, in the shot showing Ken Mattingly, Kranz can be seen in the background sitting down again in the same manner.

    * Continuity: Shortly before re-entry, a NASA worker says, " Velocity now reading 34,802 feet per second, range to go 26,025 nautical miles," and Gene Kranz has his top button done up and his tie pulled up. Before and after this shot, Kranz's shirt and tie are undone.

    * Continuity: Jack Sweigert's "NO" sign is briefly seen on the instrument panel before he actually puts it there.

    * Crew or equipment visible: When Marilyn Lovell is standing in front of the sliding glass door in her kitchen, a crew member is briefly visible on the left side of the window.

    * Incorrectly regarded as goofs: "Houston, we have a problem," is probably the world's most known misquote. After the bang, the conversation was as follows. Swigert: "Okay, Houston, we've had a problem here." Jack Lousma: "This is Houston. Say again please." Lovell: "Houston, we've had a problem. We've had a main B bus undervolt." However, this was a deliberate change suggested by Tom Hanks to better convey the sense of urgency in the scene.

    * Anachronisms: The controller giving the typhoon prediction for the landing area can be seen holding a full color satellite picture of the region. There were no color satellite pictures at the time - especially not in (near) real time.

    * Factual errors: If Ken Mattingly had viewed the launch from that close, he would not have survived.

    * Miscellaneous: At approx. 17:47, there is a photo session. The Hasselblad 500 camera used is out of film. It is shown by the red arc on the film magazine. A camera with all film unexposed should view a "metallic" arc, rather than a red one.

    * Anachronisms: The engineers add numbers with a slide rule. Calculators were already available by then.

    * Anachronisms: The USS New Orleans (a stand-in for the USS Iwo Jima) is shown with CIWS (Close In Weapons System) that was not in commission until 1977 when tested on the USS Bigelow.

    * Factual errors: As Apollo 13 approaches the Earth, the flight controllers state that it is coming in shallow because it is light, and that it is light because it never visited the moon, and thus does not contain a couple hundred pounds of moon rocks. In fact, because they never visited the moon, the LEM retains its Decent Stage, which weighs over 4700 pounds plus any remaining fuel. If anything, Apollo 13 would be too heavy.

    * Crew or equipment visible: When the astronauts are getting their suits put on for the launch, someone asks Swigert "Do you need more air?" Swigert shakes his head. As the camera zooms in slowly, a reflection of three crew members can be seen in his helmet.

    * Factual errors: The Mission Clock is not supposed to start until the Saturn V rocket lifts off the launch pad.

    * Continuity: The drawing Kranz makes on the chalkboard change shape between scenes.

    * Miscellaneous: The orientation of the spacecraft during the mid-course correction burn is not consistent to what the crew was seeing out of the Lunar Module's windows.

    * Factual errors: Before re-entry, Haise was reading voltage and amperage of the batteries. On two of the batteries there is no voltage, but he says there is some amount of amperage. Amperage cannot be present without some amount of voltage.
    Last edited: Aug 22, 2006
  12. Aug 22, 2006 #11

    Chi Meson

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    HA! I knew it! (See post #2)
    I don't think any of these are what the assignment calls for, though.
  13. Aug 22, 2006 #12
    "* Factual errors: When Jim Lovell is standing in his garden looking at the moon (one eye closed) he covers and uncovers the moon (from his perspective) with his thumb. Since the moon was the only light source in this situation, the shadow of his thumb would have to be shading his eye. But the third person perspective shows the thumb's shadow elsewhere."

    that might work :) light is part of physics
  14. Aug 22, 2006 #13


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    I believe that just before reentry, the CM is shown in an orientation that is too steep. It should have been travelling nearly parallel to the horizon. A few moments later, it is shown in the horizontal orientation.

    Wow. After reading Hedon's list I need to watch the movie again.
  15. Aug 23, 2006 #14

    * Factual errors: Before re-entry, Haise was reading voltage and amperage of the batteries. On two of the batteries there is no voltage, but he says there is some amount of amperage. Amperage cannot be present without some amount of voltage.

    That's physics.

  16. Aug 23, 2006 #15
    Physics is such a broad catelgory that almost any thing that is physical could quailfy. Some more than others though ;-)

    Here's a good one...

  17. Aug 23, 2006 #16

    Chi Meson

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    Yeh, OK. If that's the worst Physics mistake they made, they did a pretty good job.
  18. Aug 24, 2006 #17
    ...being a simple fellow, I would think that using sound effects in space is bad physics due to a vacuum does not transmit sound. So stuff fly by would do so quietly...
  19. Aug 24, 2006 #18


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    Not only would that be 'bad physics', but you calculate the escape velocity your self to check it. The specific energy has to equal 0 or higher to achieve escape velocity:

    [tex]\frac{1}{2}v^2 - \frac{GM}{r} = 0[/tex]
    You add the Moon's radius to the altitude to get the radius (r). G is the universal gravitational constant, and M is the mass of the Moon.

    As far as goofs in the goof list: You don't add numbers with a slide rule. You can multiply, divide, find powers or roots of numbers, solve quadratic equations, trig problems, and vector equations, solve problems with compex numbers in addition to real numbers, transform two and three dimensional coordinates from spherical to rectangular and vice versa, find logarithms (both natural and base 10), but you can't add or subtract.
  20. Aug 25, 2006 #19

    Andrew Mason

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    One has to keep in mind that the moon's centre of mass is not at its geometic centre. It is offset by about 2 km. So the ship could have been 1738 + 56 + 2 km from the centre of gravity.

    I calculate the escape velocity at this distance to be 7572 feet/sec.

    However, this is the velocity to escape lunar gravity completely. It didn't have to do that. All it had to do was to get to the point where the earth's gravity exceeds lunar gravity. A speed of 7052 ft/sec is sufficient for that.

    This is quite true for logarithmic scales on the slide rule. But if the slide rule has a non-logarithmic scale you could use it to add numbers. After all, the slide rule is just an adding device - used for adding logarithms. I have never seen one used that way to add numbers, however.

  21. Aug 25, 2006 #20


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    That's a good point about having to add in the Earth's gravity.

    While it's possible to create a slide rule that adds and subtracts, none were ever manufactured and sold, as far as I know. And, actually, a different list of goofs provides a better reason the use of the slide rule was a goof (even after electronic calculators were available, it was still extremely common for people to use slide rules for a couple years).


    The other list has a better physics goof, as well. A full moon out one window, with a full Earth in the opposite window.
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