Doubts about the moon landings

Has anyone explained why low gravity makes astronauts move in slow motion on the moon, but not in low earth orbit?

There are numerous videos available that show if you speed up the playback rate of astronauts allegedly walking on the moon, they appear to be moving like people walking on earth. Lone Shaman has created a nice clear example of this.

However videos of astronauts in orbit around earth in low gravity environments do not move in slow motion - why is this?

Astronauts inside the spacecraft are not wearing full spacesuits. Also, surely if you were walking in a totally alien environment, knowing that one rip in your suits is fatal, you would walk slowly - I am sure I would :)

David
 
Astronauts inside the spacecraft are not wearing full spacesuits. Also, surely if you were walking in a totally alien environment, knowing that one rip in your suits is fatal, you would walk slowly - I am sure I would :)

David
Any thoughts on pendulum physics?
 
You are only considering the conservation of energy between kinetic energy and potential energy. These are conserved as the pendulum swings downward and upward. This also is explained in the link. If you got down that far you missed the major concept that is at work in a pendulum.
This is from the link you provided (bolding is mine):

u10l0c10.gif

Take some time to inspect the bar charts shown below for positions A, B, D, F and G. What do you notice?

u10l0c12.gif

When you inspect the bar charts, it is evident that as the bob moves from A to D, the kinetic energy is increasing and the potential energy is decreasing. However, the total amount of these two forms of energy is remaining constant. Whatever potential energy is lost in going from position A to position D appears as kinetic energy. There is a transformation of potential energy into kinetic energy as the bob moves from position A to position D. Yet the total mechanical energy remains constant. We would say that mechanical energy is conserved. As the bob moves past position D towards position G, the opposite is observed. Kinetic energy decreases as the bob moves rightward and (more importantly) upward toward position G. There is an increase in potential energy to accompany this decrease in kinetic energy. Energy is being transformed from kinetic form into potential form. Yet, as illustrated by the TME bar, the total amount of mechanical energy is conserved
How can this be more clear, where would you say that gravity extracts energy from this system?


What you are missing are the two major forces at work on a pendulum, the restoring force and tension. The restoring force is gravity. It is explained in detail in the link that I posted and in your reply. It is not accurate to refer to it as damping.

u10l0c2.gif
This visually shows gravity as the restoring force. The link explicitly explains how gravity is the restoring force. It is really something that should be intuitive I would have thought. Anyway it is all there in the link.
Gravity tries to restore the pendulum to it's resting position, in that sense it is the restoring force.
But in doing so it builds up just as much kinetic energy, as it loses in potential energy, so it goes through the resting position, just as high as the original position on the other side, with just as much potential energy.

What you are selecting from this link, does not mean what you think it means (whatever that may be), it is like giving half of an equation, it does not mean anything in isolation.


The animation at the right (used with the permission of Wikimedia Commons; special thanks to Hubert Christiaen) provides a visual depiction of these principles. The acceleration vector that is shown combines both the perpendicular and the tangential accelerations into a single vector. You will notice that this vector is entirely tangent to the arc when at maximum displacement; this is consistent with the force analysis discussed above. And the vector is vertical (towards the center of the arc) when at the equilibrium position. This also is consistent with the force analysis discussed above.
Pendulum_animation.gif

This is what these force vectors resolve to, again, from the same link you provided.

So, in the absence of friction, atmosphere, vibration, etc., a pendulum goes forever.
You don't believe me? No problem, believe the very evidence you provided, believe physics.
And believe everybody else but you.

As Malf advised, seek help from someone who knows more about physics than you.

And most importantly, ask yourself where the energy is supposed to go if gravity takes it away.
That is the only question i would like to see answered, if you are interested in continuing this conversation.
 
Has anyone explained why low gravity makes astronauts move in slow motion on the moon, but not in low earth orbit?

There are numerous videos available that show if you speed up the playback rate of astronauts allegedly walking on the moon, they appear to be moving like people walking on earth. Lone Shaman has created a nice clear example of this.

However videos of astronauts in orbit around earth in low gravity environments do not move in slow motion - why is this?
The reason astronauts walk (jump) so slow, is te same as why a pendulum swings slower on the moon, it's gravity.
If they take one of these unique jumpsteps, they accelerate an decelerate slower in 1/6 G , so they have more "airtime".
Therefore they seem to move slower for locomotion. The rest of their movement is hindered by bulky pressurized suits, but is not necessarily always slower than on earth.

In the low earth orbit weightlessness, they can freely move, and do not have to move by stepping
They float and can accelerate by pushing from walls.
 
The formula for the period of oscillation of an ideal pendulum is T=2pi Sqrt(L/g) - so self evidently if g is smaller the oscillation will be slower. There are pages and pages of this thread devoted to this subject, and I can't be bothered to figure out who is trying to argue what! I'd also say the swing would be less damped in a vacuum due to lack of air friction, but who really knows how much friction comes from the attachment.

https://en.wikipedia.org/wiki/Pendulum

Which side (if any) have I supported?

David
 
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A common observation: the more socially and morally charged the issue is, the more difficult discussion becomes even for the people with higher-than-average level of self-reflexivity and open-mindedness (e.g., the type people who gather here on Skeptiko).

Agreed, and yet paradoxically the question of morality should cleanly factor out in any debate. I mean (using CAGW as an example) I don't wish the planet to be harmed, but I don't believe in CAGW. If I did believe in CAGW, I'd be out with the climate change protestors. My belief in CAGW does not really depend on my moral position.

Traditionally CAGW 'deniers' are demonised, but I think it is obvious that we simply don't agree with the conclusion of the IPCC.

The moon landing question is less charged, but I hope that LS is wrong on this question, but if he is right, I want to know that too.

David
 
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The formula for the period of oscillation of an ideal pendulum is T=2pi Sqrt(L/g) - so self evidently if g is smaller the oscillation will be slower. There are pages and pages of this thread devoted to this subject, and I can't be bothered to figure out who is trying to argue what! I'd also say the swing would be less damped in a vacuum due to lack of air friction, but who really knows how much friction comes from the attachment.

https://en.wikipedia.org/wiki/Pendulum

Which side (if any) have I supported?

David

You've basically supported team "this is as expected on the moon, not an anomaly due to filming on Earth near an air vent".

Early on, we used that formula to confirm that the approximate period of oscillation of the swinging bag is compatible with the moon's gravity, not Earth gravity.

Too, we have, as you have done, contended that the swing on the moon is less damped than on Earth due to lack of air resistance (as well as due to less friction at the pivot point due to lower gravity), such that its seeming lack of damping is as expected on the moon.

There is more that is not related to your post, so I won't reiterate that unless you want me to.
 
Nowhere there does it say gravity is damping. You’re imbuing the text with what you want to be true.

Again:
https://physics.stackexchange.com/q...m-swing-indefinitely-in-a-frictionless-vacuum

It is clear. If one can rule out all other damping effects, gravity will power the pendulum indefinitely. You’re totally on your own here, that should give you pause.

Right or wrong, the article clearly describes what I was saying exactly.

Gravity works on the pendulum while it is moving. The moving force becomes less as the force of gravity acts on the pendulum. The pendulum slows and then returns to the starting point. This swinging-back-and-forth force continues until the force that started the movement is not stronger than gravity, and then the pendulum is at rest again.
Gravity isn’t pulling the pendulum back to return to the beginning point along the same path. The force of gravity is pulling the pendulum down toward the Earth.
Gravity isn’t pulling the pendulum back to return to the beginning point along the same path. The force of gravity is pulling the pendulum down toward the Earth.
 
This is from the link you provided (bolding is mine):


How can this be more clear, where would you say that gravity extracts energy from this system?



Gravity tries to restore the pendulum to it's resting position, in that sense it is the restoring force.
But in doing so it builds up just as much kinetic energy, as it loses in potential energy, so it goes through the resting position, just as high as the original position on the other side, with just as much potential energy.

What you are selecting from this link, does not mean what you think it means (whatever that may be), it is like giving half of an equation, it does not mean anything in isolation.



Pendulum_animation.gif

This is what these force vectors resolve to, again, from the same link you provided.

So, in the absence of friction, atmosphere, vibration, etc., a pendulum goes forever.
You don't believe me? No problem, believe the very evidence you provided, believe physics.
And believe everybody else but you.

As Malf advised, seek help from someone who knows more about physics than you.

And most importantly, ask yourself where the energy is supposed to go if gravity takes it away.
That is the only question i would like to see answered, if you are interested in continuing this conversation.

I already explained the conversation of Energy. The ratios of potential energy and kinetic energy simply change.

The site also includes the graphic of the sine wave of position over time.
u10l0c6.gif
 
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To put things in perspective what we are arguing about is theoretical abstraction vs reality.

These arguments of perpetual motion are theoretical just as the simple pendulum is a mathematical construct.

Steve posted a video of a pendulum in a vacuum chamber, it does not go forever, a atmosphere made little difference in the case of the metallic bob. whether it slows it totally because of friction or not seems of little consequence to the issue that started this.

You can't show a perpetual motion machine, you can only show what is the abstraction, a construct.

All this was started because of the swinging ETB bag, It does not slow down at all.

So we have to do mental back flips and switch into the safety of abstraction to avoid reality.

Then we would have to begin denying that friction will also have no effect.

We would also have to stretch yet again to claim that such a set up, a bag hooked at two points is somehow equivalent to a perfect harmonic oscillator.
 
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All this was started because of the swinging ETB bag, It does not slow down at all.

Firstly, somebody who doesn't want to post publicly has been in touch with me privately to let me know that after careful and meticulous frame-by-frame analysis, this person has determined that your claim that the extent of the bag's swing does not diminish by even a pixel is false, and that a slowing down can be detected.

Secondly, even if the bag were not slowing at all, your explanation for why this is does not work, as I pointed out in this post. To reiterate: if, as you suggest, a constant force like air from an air vent were blowing on the bag on Earth, that force would have opposite effects when the bag was swinging away from it compared to when the bag was swinging towards it - effects which would cancel each other out (though they would tend to shift the midpoint of the bag's arc slightly in the direction of the airflow). So, a constant force from an air vent would not (as with gravity!) serve to impart any net additional energy to the bag, and thus would not act to maintain its period and prolong its motion. Your hypothesis is false.

A correct hypothesis would involve two forces, on opposite sides of the bag, each one timed to be operative only when the bag was swinging in the same direction as the force, and with just enough magnitude to exactly cancel out the dissipative force of friction - otherwise they would, instead, cause the bag's period to increase rather than stay the same. This is basically how clock pendulums are kept running indefinitely. As I think is obvious, this scenario is not plausible, especially given the situation in the video, where it's not clear what could provide the force from the astronaut's side of the bag.

Too, as I pointed out again in my last post, we have the evidence that the bag's period is roughly what we would expect on the moon, and not the Earth, so that pretty much clinches it.
 
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Firstly, somebody who doesn't want to post publicly has been in touch with me privately to let me know that after careful and meticulous frame-by-frame analysis, this person has determined that your claim that the extent of the bag's swing does not diminish by even a pixel is false, and that a slowing down can be detected.

Can this someone supply the calculated period of oscillation? That would all that would be required to verify it. Supply the period duration, then these cycles can be lined up exactly with the footage to see if they match. Then we can subtract the difference in the frames that align to the period. This is what I have already done.

I will eventually detail my analysis in a video, showing exactly how it is done. There is no way to cheat because it must conform to the footage exactly, before frames can be subtracted. Even a slight miscalculation will result in a mismatch.

The rest of your post regarding a external force having no net effect is just silliness. There is so much there you are not taking into account I could not be bothered with it. This is a sideline of no consequence. I do not have to explain why the bag does not slow. You do. Forgive me for finding your interpretation of things not very credible. Give some actual reference and source instead of your opinion.

You are simply denying that the bag does not slow. Give me the period time and we can check. Easy.

Too, as I pointed out again in my last post, we have the evidence that the bag's period is roughly what we would expect on the moon, and not the Earth, so that pretty much clinches it.

The only factor affecting the period are length and gravity. We have no conclusive way to determine this because the length is from the pivot point to the center of mass. The mass in the bag would be unevenly distributed so there is no way to resolve exactly where the center of mass is. I love how just reference yourself as a source.

You also must assume that it is on the moon and what we are seeing is actually the true time and not a different frame rate used to replicate the moon. There is nothing about lunar gravity or the suits that should cause one to move in what is obviously just slow motion.

The main point in all this is a rejection of this....

ETB-bagGif.gif
 
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Can this someone supply the calculated period of oscillation?

The approach this person took was to extract all frames from a 36-second interval of the bag's swinging, ending up with 565 individual frames, and to then examine each one to pick out the point of maximum swing. This resulted in 12 frames. By selecting every third frame of these, resulting in four frames, and running them as a video, this person determined that "there is a very clear and gradual reduction of amplitude with time".

The rest of your post regarding a external force having no net effect is just silliness.

A comment like that simply reveals your ignorance. I'm not writing to be offensive, it's the simple truth. Again, ask your local high school's physics teacher if you don't believe me. Seriously. Consult somebody who knows.

Or, look into clock pendulums and how they are kept running indefinitely. You will find that it is (of necessity) not by supplying a constant force in one direction, but by supplying alternate forces in opposite directions at each extreme of the swing.

I do not have to explain why the bag does not slow.

You have to explain why the bag not slowing - if, indeed, that is the case - means that the bag is on the Earth rather than the moon. How does this particular phenomenon prove your primary thesis (that the footage was filmed on Earth)?
 
The approach this person took was to extract all frames from a 36-second interval of the bag's swinging, ending up with 565 individual frames, and to then examine each one to pick out the point of maximum swing. This resulted in 12 frames. By selecting every third frame of these, resulting in four frames, and running them as a video, this person determined that "there is a very clear and gradual reduction of amplitude with time".



What I would like is the calculated time for each oscillation. This is how it can be verified.

36 x 24 = 864 frames

Where does this 565 frames come from?

You cannot just guess where the maximum point of swing is, it should be precisely indicated by the period of oscillation. No guessing allowed.
 
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What I would like is the calculated time for each oscillation.

I don't see what advantage that's going to give us over the approach this person has taken, but I can see whether this person has kept frame numbers for each frame of maximum amplitude. That would make it possible to calculate the period.
 
I don't see what advantage that's going to give us over the approach this person has taken, but I can see whether this person has kept frame numbers for each frame of maximum amplitude. That would make it possible to calculate the period.

Because it is just guessing, you cannot just guess at what frame is the maximum point of swing it has to be established by the precise period of oscillation. Not the other way around.

This was not done in your friends analysis. This is just subjective guess work.

Also

36 x 24 = 864 frames not 565,
 
Because it is just guessing, you cannot just guess at what frame is the maximum point of swing

There was no guessing involved, simply a careful comparison of frames to determine the ones in which the bag reached its maximum amplitude.

36 x 24 = 864 frames not 565

If you say so. I don't know. I didn't perform the analysis and I'm not an expert on video. I will ask about that.
 
There was no guessing involved, simply a careful comparison of frames to determine the ones in which the bag reached its maximum amplitude.

That is guessing. I counted frames by guessing and it resulted in a range of 31 to 39 frames. It quickly became apparent you just can't do it that way. It is subjective. The peaks have to be determined by the period. If the period is out by even just a fraction it results in a mismatch.

My analysis is mathematically precise, with no subjective input. I let the numbers do the work and not my own judgement.

If you say so. I don't know. I didn't perform the analysis and I'm not an expert on video. I will ask about that.

This was not a analysis, it was guess work. Worthless.
 
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