Why does the flag on the moon appear to be waving during the Apollo 13 mission?

In summary: I'm afraid there's no easy answer, but you could try to compute the resistance for a given wind speed and area.Well, "flag+moon" is certainly a bad idea to search for on the internet. Maybe someone once did a calculation for fun, but the chances to find it are basically zero. I don't even know, what material the flags are made of - maybe it's aluminium. However, this could probably be found out, e.g. on the NASA page, but then it's getting difficult: How long does a flag wave in the air without wind? It's probably far easier to rebuild such a flag, shut windows and doors. stop moving and wait until it stops moving. In this case it stopped mainly
  • #1
Physics345
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Hi Everyone,

Can someone please explain to me why the flag is moving as if wind is blowing on it during the Apollo 13 mission?

I am well aware that it's not actually wind blowing on the the flag causing it to move, but I still would love to know why this occurs.

Note: I am very uneducated on this subject, a simple answer would be appreciated.

Best Wishes, and Thank you.
Physics345
 
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  • #2
Nice try. There is no Apollo 13 flag on the moon.
 
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  • #3
fresh_42 said:
Nice try. There is no Apollo 13 flag on the moon.
So that video with the astronauts placing a USA flag on the surface is fake?
Edit: Oops, I may have mixed up Apollo 13 and 15.
 
  • #4
Physics345 said:
Hi Everyone,

Can someone please explain to me why the flag is moving as if wind is blowing on it during the Apollo 13 mission?

Reference please. When are you talking about?
 
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  • #5
CWatters said:
Reference please. When are you talking about?

Like I said, I'm very uneducated on this topic, that's why I'm here to get a better understanding of it.
 
  • #6
If you mean this video...



It only moves when it's handled or an astronaut knocks it when going past at the end. That sets it swinging but it soon stops and becomes motionless.
 
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  • #7
CWatters said:
If you mean this video...



It only moves when it's handled or an astronaut knocks it when going past at the end. That sets it swinging but it soon stops and becomes motionless.


Oh okay, so basically a force is acting upon it causing it to move and eventually the force dissipates causing it to become motionless.

Considering the gravity on the moon, the small margin of friction in this scenario, and the low amount of gravity (1.62 m/s^2) present on the moon wouldn't it start to become motionless over a longer period of time?

Is there any math that proves the amount of time it would take for it to become motionless? (Math that takes all the factors into account, such as the force acting upon it, gravity, and etc)
 
  • #8
Also I am aware that I sound very ignorant on the topic, but learning has to start somewhere, and I'd rather get some information from experienced/knowledgeable people on here, rather than reading crackpot articles spread over the internet.
 
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  • #9
Physics345 said:
Is there any math that proves the amount of time it would take for it to become motionless?
The math is loss by fiction, but the actual calculation is practically impossible, as it depends on too many unknowns, resp. constants which can only be measured by experiment. I think they had a stiff part at the top to keep the flag open and the movements are due to moving the whole thing, either as they put it there or afterwards when touched. The continuous friction by the material will stop it, as it applies a negative force to the system. It will only move again if hit by something.
 
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  • #10
fresh_42 said:
The math is loss by fiction, but the actual calculation is practically impossible, as it depends on too many unknowns, resp. constants which can only be measured by experiment. I think they had a stiff part at the top to keep the flag open and the movements are due to moving the whole thing, either as they put it there or afterwards when touched. The continuous friction by the material will stop it, as it applies a negative force to the system. It will only move again if hit by something.
Hmm, that definitely makes sense, there are many unknown measurements in this case. I guess in the future, when we create a base on the moon we will be able to conduct more practical experiments such as these.
Is there any way to make a rough estimate, of the unknown variables leading to a vague hypothetical mathematical answer?
 
  • #11
I would like to also state that, my line of questioning behind the math, stems from the origin of having an answer to disprove peoples ideas of the moon landing being fake due to the flags motion.
 
  • #12
Physics345 said:
Is there any way to make a rough estimate, of the unknown variables leading to a vague hypothetical mathematical answer?
Well, "flag+moon" is certainly a bad idea to search for on the internet. Maybe someone once did a calculation for fun, but the chances to find it are basically zero. I don't even know, what material the flags are made of - maybe it's aluminium. However, this could probably be found out, e.g. on the NASA page, but then it's getting difficult: How long does a flag wave in the air without wind? It's probably far easier to rebuild such a flag, shut windows and doors. stop moving and wait until it stops moving. In this case it stopped mainly due to air resistance. The formula for pressure resistance is ##F_p= \Delta p \cdot A_p## with pressure ##p## and area ##A_p##. This is something we can compute. So ##F_0=m\cdot a - F_p## with the initial push ##F_0## and the mass ##m## of the flag give us a deceleration ##a##. So all we need is an estimate about the initial velocity of movement which is stopped by ##a## after some time.

You see how many unknowns are within such a calculation and how many estimations have to be made. And I only used the pressure resistance by air here. There is probably also a resistant component from the material itself. However, I have the strong feeling that even a flag manufacturer on Earth doesn't know the resistance coefficient of his tissue.
 
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  • #13
fresh_42 said:
Well, "flag+moon" is certainly a bad idea to search for on the internet. Maybe someone once did a calculation for fun, but the chances to find it are basically zero. I don't even know, what material the flags are made of - maybe it's aluminium. However, this could probably be found out, e.g. on the NASA page, but then it's getting difficult: How long does a flag wave in the air without wind? It's probably far easier to rebuild such a flag, shut windows and doors. stop moving and wait until it stops moving. In this case it stopped mainly due to air resistance. The formula for pressure resistance is ##F_p= \Delta p \cdot A_p## with pressure ##p## and area ##A_p##. This is something we can compute. So ##F_0=m\cdot a - F_p## with the initial push ##F_0## and the mass ##m## of the flag give us a deceleration ##a##. So all we need is an estimate about the initial velocity of movement which is stopped by ##a## after some time.

You see how many unknowns are within such a calculation and how many estimations have to be made. And I only used the pressure resistance by air here. There is probably also a resistant component from the material itself. However, I have the strong feeling that even a flag manufacturer on Earth doesn't know the resistance coefficient of his tissue.
That is a very logical and unbiased answer. This shows and explains what i meant about crackpot articles on the internet vs the information I can gather here about this topic. Anyways, based on the unknown factors present in this topic/question we can conclude that it would be a timely process to derive such calculations based on the known factors and possible hypothetical unknowns, where the hypothetical variables are the most challenging to re-create and/or come to a logical assumption, which would allow a relatively accurate mathematical answer. Overall the math could be done, but it is not worth the time it would take to disprove crack pot hypothesis, because there is no benefit of doing so, since people will always believe what they want to believe.
 
  • #15
Physics345 said:
Oh okay, so basically a force is acting upon it causing it to move and eventually the force dissipates causing it to become motionless.

Considering the gravity on the moon, the small margin of friction in this scenario, and the low amount of gravity (1.62 m/s^2) present on the moon wouldn't it start to become motionless over a longer period of time?

Lower gravity changes the period of a pendulum making it swing slower. It doesn't make it stop quicker. The energy will dissipate at a rate that depends on the stiffness of the material and how its suspended. Difficult to quantify.

Is there any math that proves the amount of time it would take for it to become motionless? (Math that takes all the factors into account, such as the force acting upon it, gravity, and etc)

Not really and anyway no calculation would ever satisfy some people.
 
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  • #16
CWatters said:
Lower gravity changes the period of a pendulum making it swing slower. It doesn't make it stop quicker. The energy will dissipate at a rate that depends on the stiffness of the material and how its suspended. Difficult to quantify.
Good to know, you learn something new everyday =).

CWatters said:
Not really and anyway no calculation would ever satisfy some people.
I totally agree, no matter what you do people will believe what they want to believe and they have every right to believe what they want.

CWatters said:
Google says the flags were made of Modal.

https://www.hq.nasa.gov/alsj/ApolloFlags-Condition.html

Shadows on photos show they were still "flying" in 2011.
That's interesting. Thanks for taking your time to find that out for me. It could very well be the first step to figuring out hypothetical calculations, if I ever do decide to venture into that route as a personal project for fun, but that will have to wait until I have acquired a wider range of mathematics knowledge.
 
  • #17
The simple answer is that parts of the flag were moving when it was first placed by the astronaut.
Residual momentum acquired by the simple act of it being moved by the astronaut.
It only persisted for a few seconds
 
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  • #18
CWatters said:
Google says the flags were made of Modal.

https://www.hq.nasa.gov/alsj/ApolloFlags-Condition.html

Shadows on photos show they were still "flying" in 2011.

That link says the opposite:
(LRO Camera Principal Investigator, Dr. Mark) Robinson is skeptical that the flags are intact, if they are still there.
 
  • #19
Consider a simple pendulum. After you set it swinging, its amplitude of motion decreases slowly, and it eventually comes to a stop. Air friction is the first thing that comes to mind as a cause, but there are also frictional losses inside the string, especially at the upper end where it flexes back and forth. Here's a video that compares the motion of pendulums in air and in vacuum:

 
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  • #20
rootone said:
The simple answer is that parts of the flag were moving when it was first placed by the astronaut.
Residual momentum acquired by the simple act of it being moved by the astronaut.
It only persisted for a few seconds
Basically in physics terms work was applied then the energy dissipated, in turn leading to a motionless flag correct?
 
  • #21
jtbell said:
Consider a simple pendulum. After you set it swinging, its amplitude of motion decreases slowly, and it eventually comes to a stop. Air friction is the first thing that comes to mind as a cause, but there are also frictional losses inside the string, especially at the upper end where it flexes back and forth. Here's a video that compares the motion of pendulums in air and in vacuum:


That is a very interesting video, so we we could say so far we have two obvious sources of coefficient static friction in this case.
1. Air friction.
2. Tension friction from the string. (which is caused by the motion of the flag leading to the temperature of the string rising)
Okay I understand how the tension friction is occurring, but how is there air friction on the moon? I was under the assumption there is no type of air resistance on the moon, since there is no air on it.
 
  • #22
Physics345 said:
Basically in physics terms work was applied then the energy dissipated, in turn leading to a motionless flag correct?

Sunlight will apply between 5 and 9 micro Newtons pressure. The solar wind is variable. There are moon quakes. Static electricity can build up on the moons surface.

The fibers should disintegrate and land near the flagpole. Many of the original atoms will have gassed of and moved into deep space. A few molecules may bind with regolith or possibly settle in a crater near the north or south pole.

The flag is also orbiting Earth and it is moving ≈370km/s relative to cosmic background.
 
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  • #23
stefan r said:
Sunlight will apply between 5 and 9 micro Newtons pressure. The solar wind is variable. There are moon quakes. Static electricity can build up on the moons surface.

The fibers should disintegrate and land near the flagpole. Many of the original atoms will have gassed of and moved into deep space. A few molecules may bind with regolith or possibly settle in a crater near the north or south pole.

The flag is also orbiting Earth and it is moving ≈370km/s relative to cosmic background.
All of those are definitely variables, but wouldn't the moon quakes be noticed by the astronauts leading to some type of panic, which would be evident in the video?
Next the solar wind. If I'm not mistaken solar wind is extremely hot and if solar wind were to hit the moon while they were there wouldn't their suits melt or wouldn't they be vaporized (not sure if vaporized is the right word for this scenario)? I am asking this because I remember reading that the moon does not have an atmosphere so nothing would protect the astronauts suits from direct contact with the solar wind in this case. If this is true we can factor out solar wind.
Also is the sunlight's pressure a constant occurrence?
 
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  • #24
I would like to take a moment and thank everyone that has taken their time to input different pieces of information into this discussion. I am having a lot of fun, this has become a very engaging and interesting thread!
 
  • #25
Physics345 said:
Also is the sunlight's pressure a constant occurrence?

Sunlight is nearly constant. The pressure on the flag would vary by angle.
Gravity on the moon is 1.62 m/s2 if the flag had 1 gram of mass the force would be 1620 microNewtons. If the flag was positioned north-south so you have full exposure at sunrise and sunset and if the flag is bleached enough a 1 m2 flag could experience 8.1 microNewtons. That is one part in 200. It probably has more mass and probably is not perfectly north-south. The effect would be measured in mm or less.

Physics345 said:
If I'm not mistaken solar wind is extremely hot and if solar wind were to hit the moon while they were there wouldn't their suits melt or wouldn't they be vaporized (not sure if vaporized is the right word for this scenario)?

Solar wind is hot enough to melt suits. The density of the solar wind is much lower than the density of the suit/astronaut. The suits were painted white to reflect radiation. They emitted thermal radiation which was mostly from sunlight and body heat. You need to radiate heat. If a human body is fully insulated it gets cooked and dies.

Physics345 said:
All of those are definitely variables, but wouldn't the moon quakes be noticed by the astronauts leading to some type of panic, which would be evident in the video?
I live in Pennsylvania, USA. The seismograph I looked at a few weeks ago says we are constantly having quakes. I have never felt them here.
Moonquakes:
Between 1972 and 1977, the Apollo seismic network saw twenty-eight of them; a few "registered up to 5.5 on the Richter scale,
The lunar lander was on shock absorbers. 5.5 would not be very alarming while walking around. They were on the surface for about 3 days. 5 quakes per year is not likely to coincide with the landing.
 
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  • #26
Physics345 said:
If this is true we can factor out solar wind.
As far as I know, the solar wind is so weak that it requires solar sails of hundreds of metres square to catch enough of it to accelerate a tiny spacecraft at a moderate rate. If the wind was enough to shake that flag then there would be dust flying all over the Moon's surface. Did you ever notice any on the films? The dust is extremely fine, you know.
There is just not enough information to determine how long a sheet of unknown material and unknown construction, on a light, whippy support, could carry on shaking if it were nudged. The movie is not long enough to reveal the real situation but Occam's Razor, when applied to all of this nonsense tells us that it really was waving and it really was on the surface of the Moon.
I have to question the motives and the sense of people who are still looking for evidence that it never happened. There must be fairies at the bottom of their gardens.
 
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  • #27
stefan r said:
Solar wind is hot enough to melt suits. The density of the solar wind is much lower than the density of the suit/astronaut. The suits were painted white to reflect radiation. They emitted thermal radiation which was mostly from sunlight and body heat. You need to radiate heat. If a human body is fully insulated it gets cooked and dies.

We're getting closer to factoring out solar wind. Good work.

stefan r said:
The lunar lander was on shock absorbers. 5.5 would not be very alarming while walking around. They were on the surface for about 3 days. 5 quakes per year is not likely to coincide with the landing.

Well we can factor out moon quakes as well then, unless someone has some input that can change that.

stefan r said:
Sunlight is nearly constant. The pressure on the flag would vary by angle.
Gravity on the moon is 1.62 m/s2 if the flag had 1 gram of mass the force would be 1620 microNewtons. If the flag was positioned north-south so you have full exposure at sunrise and sunset and if the flag is bleached enough a 1 m2 flag could experience 8.1 microNewtons. That is one part in 200. It probably has more mass and probably is not perfectly north-south. The effect would be measured in mm or less.
Well we could easily find out where they landed, through some light research which I will do right after, I'm done practicing calculus.

sophiecentaur said:
I have to question the motives and the sense of people who are still looking for evidence that it never happened. There must be fairies at the bottom of their gardens.

I agree but, like I said previously people can believe what they want. Even though what they believe has a mountain load of evidence against it, but regardless as soon as that right is taken away from people we will have reverted to a dated mind set. Overall in my opinion these types of people are very simple minded they don't bother doing any type of factual research which most likely stems from low intelligence due to nurture and is most likely hereditary as well.

sophiecentaur said:
As far as I know, the solar wind is so weak that it requires solar sails of hundreds of metres square to catch enough of it to accelerate a tiny spacecraft at a moderate rate. If the wind was enough to shake that flag then there would be dust flying all over the Moon's surface. Did you ever notice any on the films? The dust is extremely fine, you know.

Good work, with that we can definitely factor out solar wind.

sophiecentaur said:
There is just not enough information to determine how long a sheet of unknown material and unknown construction, on a light, whippy support, could carry on shaking if it were nudged.

The whole point is to construct a hypothetical analysis with as much known variables as possible, with what ever information we can find. The rest would have to be "Educated Assumptions" at best and even then to follow Occam's Razor we would need to limit the assumptions as much as possible. Regardless has enough research been done into this topic to determine with absolute certainty that it is indeed "impossible" to create a hypothetical analysis?
 
  • #28
Physics345 said:
with as much known variables as possible,
AND without the inappropriate preconceptions about how one sort of flag behaves on Earth and automatically applying them another thing that people are calling a flag when it's on the Moon.
This is all a serious waste of good thinking time, you know.
 
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  • #29
sophiecentaur said:
AND without the inappropriate preconceptions about how one sort of flag behaves on Earth and automatically applying them another thing that people are calling a flag when it's on the Moon.
This is all a serious waste of good thinking time, you know.
Well I've stated previously it may not be worth the time it would take to construct such an analysis for various reasons. People seem to be interested in the topic, so why would we stop discussing it? Engaging the mind can never be considered to be a waste of time. At the end of the day it is good practice, which could lead to something greater, if not in this topic but possibly another.
 
  • #30
I know that the flags were folded and compressed tight for stowage during launch, so there would be time involved with the creases slowly working themselves out in the lower gravity. They likely used a lightweight material, even so, it would have creased along fold lines, and these relaxing "may" give slight motion to the flag without it being touched. The thermal changes daily (lunar day) would help in that, but it would not be on a personally observable timescale for us here on Earth. Other than that, yes, the motions were mostly when the stand or flag was bumped or when inadvertent dust was kicked up (which was actually a problem at first).

And while there has been found to be a micro-atmosphere of xenon, helium and OH+ radicals, even that is not enough to make the flags wave in normal conditions.
 
  • #31
sophiecentaur said:
...then there would be dust flying all over the Moon's surface. Did you ever notice any on the films?...There must be fairies at the bottom of their gardens.

There is dust flying over the moon's surface. :-p

Here is a picture from clementine with Venus in the background:

220px-ClementineObservesTheMoonSolarCoronaAndVenus.jpg


The Apollo astronauts who saw it first were not sure what to make of it.
 

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  • #32
Physics345 said:
I would like to also state that, my line of questioning behind the math, stems from the origin of having an answer to disprove peoples ideas of the moon landing being fake due to the flags motion.
I'm sure everyone is aware of where the question comes from...
Physics345 said:
Hmm, that definitely makes sense, there are many unknown measurements in this case. I guess in the future, when we create a base on the moon we will be able to conduct more practical experiments such as these.
Is there any way to make a rough estimate, of the unknown variables leading to a vague hypothetical mathematical answer?
I don't know why you'd even bother. It's obvious that the violent shaking of the astronaut is making it move. The damping time really doesn't matter unless you're trying to argue against a silly idea like that a gust of wind occurred just as the astronaut was violently shaking the flag, and then the wind completely stopped. It's a silly/convoluted idea that should not be worthy of debunking.
Regardless has enough research been done into this topic to determine with absolute certainty that it is indeed "impossible" to create a hypothetical analysis?
No, I'm quite certain no serious researcher would bother with this.
People seem to be interested in the topic, so why would we stop discussing it? Engaging the mind can never be considered to be a waste of time.
Well, for one, it violates PF rules. From a practical standpoint, people have only finite brain power, so if they are working on this silly problem they aren't addressing the many better problems that are out there to be answered. PF is about quality, not quantity.

Thread locked.
 
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1. Why does the flag on the moon appear to be waving during the Apollo 13 mission?

This is a common misconception, as the flag on the moon was not actually waving. The flag was made of a lightweight material and had a horizontal rod at the top to keep it extended. When the astronauts were planting the flag, they twisted the pole back and forth to get it into the ground, which caused the flag to ripple and appear as though it was waving. However, since there is no atmosphere on the moon, there is no wind to make the flag wave.

2. Did the astronauts intentionally make the flag appear to be waving?

No, the astronauts did not intentionally make the flag appear to be waving. As mentioned before, the flag was made of a lightweight material and the astronauts were simply trying to get it into the ground. They did not expect the flag to ripple as it did.

3. Why didn't NASA use a more sturdy flag for the Apollo 13 mission?

The flag used for the Apollo 13 mission was specifically designed for use on the moon. It needed to be lightweight so that the astronauts could easily carry and plant it. Additionally, since there is no wind on the moon, a sturdier flag would not have made a difference in terms of waving.

4. Is there any footage of the flag on the moon waving during the Apollo 13 mission?

Yes, there is footage of the flag appearing to wave during the Apollo 13 mission. However, this is simply an optical illusion caused by the astronauts twisting the pole to get it into the ground.

5. How did the flag stay upright on the moon without wind?

The flag was designed with a horizontal rod at the top to keep it extended. This, along with the lightweight material, allowed the flag to stay upright on the moon's surface without the need for wind.

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