Doubts about the moon landings

It would mean a friction-less pivot point a mass-less string, operate in a vacuum, and all mass at the lowest point of the pendulum. In these conditions it would go on forever.

Bart, my physics is rusty, so I might be wrong here, but aren't the conditions in your quote which I've bolded superfluous? If not, why not?
 
Bart, my physics is rusty, so I might be wrong here, but aren't the conditions in your quote which I've bolded superfluous? If not, why not?
They probably are for all practical purpose.
I have almost no physics education at all, i provide guesses.
You provided educated guesses in this thread, so your physics knowledge would already be at least one level higher.

This guy explained the difference to me:

Ideal pendulum:



Physical pendulum:


 
They probably are for all practical purpose.

Yep, and, I think, for all theoretical purposes too.

I have almost no physics education at all, i provide guesses.
You provided educated guesses in this thread, so your physics knowledge would already be at least one level higher.

I studied physics both in high school and in my first couple of years at university, as part of a Bachelor of Computer Systems Engineering, which I never ended up completing. But, like I said, my physics is very rusty now: that was over two decades ago, and I have done nothing to maintain my one-time skill. Still, the basics don't leave you: conservation of total energy; dissipation of energy (via friction, heat, and sound), etc.

I do remember that I studied the ideal pendulum equation in high school, though I had to look it up again to remember it, prompted by my anonymous source who provided the (as-yet uncontested, and, to my mind, valid as a rough approximation) back-of-the-envelope calculations of this post.

This guy explained the difference to me

Super stuff. He did a great job of explaining the calculations - those of the second video, I have no recollection of ever studying, though that might just be the result of two decades of collected brain fluff.

I still maintain that with regard to energy dissipation:

  1. It doesn't matter whether the string has mass or not (in the second video, the "string" has mass, and I don't think that - compared to a massless string - this has any bearing on whether or not in a vacuum the pendulum would persist in perpetual motion).
  2. It doesn't matter whether or not the mass is otherwise clustered in a point at the end of the "string" (again, in the second video, not all of the mass is clustered at the end - some of it is distributed in the "string" - and, again, I don't think that this has any bearing on whether or not in a vacuum the pendulum would persist in perpetual motion).

I am impressed though by the physics understanding that you have picked up as someone with no physics education. Kudos. Other than what I've nitpicked, I can find no fault with your posts to this thread on this topic.
 
Yep, and, I think, for all theoretical purposes too.



I studied physics both in high school and in my first couple of years at university, as part of a Bachelor of Computer Systems Engineering, which I never ended up completing. But, like I said, my physics is very rusty now: that was over two decades ago, and I have done nothing to maintain my one-time skill. Still, the basics don't leave you: conservation of total energy; dissipation of energy (via friction, heat, and sound), etc.

I do remember that I studied the ideal pendulum equation in high school, though I had to look it up again to remember it, prompted by my anonymous source who provided the (as-yet uncontested, and, to my mind, valid as a rough approximation) back-of-the-envelope calculations of this post.



Super stuff. He did a great job of explaining the calculations - those of the second video, I have no recollection of ever studying, though that might just be the result of two decades of collected brain fluff.

I still maintain that with regard to energy dissipation:

  1. It doesn't matter whether the string has mass or not (in the second video, the "string" has mass, and I don't think that - compared to a massless string - this has any bearing on whether or not in a vacuum the pendulum would persist in perpetual motion).
  2. It doesn't matter whether or not the mass is otherwise clustered in a point at the end of the "string" (again, in the second video, not all of the mass is clustered at the end - some of it is distributed in the "string" - and, again, I don't think that this has any bearing on whether or not in a vacuum the pendulum would persist in perpetual motion).

I am impressed though by the physics understanding that you have picked up as someone with no physics education. Kudos. Other than what I've nitpicked, I can find no fault with your posts to this thread on this topic.
Agreed, if i understand correctly, the only difference is that the physical pendulum equation gets more complicated because part of it averages out the weights, to get to the correct pendulum length.
 
Agreed, if i understand correctly, the only difference is that the physical pendulum equation gets more complicated because part of it averages out the weights, to get to the correct pendulum length.

Yes. Exactly right, as I understand it - at least, in a manner of speaking (it doesn't exactly average out the weights to get the correct pendulum length, but you could certainly transform it into a form of the ideal pendulum equation which did have an "averaged" weight and "correct" pendulum length).
 
Does a bouncing ball bounce forever in a vacuum?

No, a bouncing ball does not bounce forever in a vacuum - because the structural chaos of the elastic foam or material involved would convert the Young's Modulus of potential energy and the kinetic energy of gravity also into mechanical entropy upon each compression and release - not just 100% into another bounce. This is a form of 'internal friction' (actually it is an inefficiency of elasticity) much akin to the movement of the oceans upon the Earth - which slows our rotation and causes us to have to add leap seconds every so often. The Earth is not 'rubbing against space' but rather dissipating kinetic energy inside a closed system, through the elasticity of its oceans.

(Color commentary: And if you notice - we have had to add leap seconds over the last 60 years of 'heating up fast' at a rate FAR above what would have been justified over the eons. This is a clue into a change in mass of the Earth's outer rotating body - and a clue into climate change, if we would only look.)
 
Last edited:
Sorry haven't read all the posts yet, in a rush.

Not all things are equal because there is no such thing as a simple pendulum. That is just a mathematical model for simplicity. Which is just time, length, amplitude and gravity. So gravity is the major player in this scenario along with acceleration. Length just affects speed. Force is directly proportional to mass.

Remember that the force of gravity is downward (for the sake of simplicity). Gravity will want to align whatever in this direction.

For a compound pendulum there is a lot to consider beyond these. The structure of the support and material as it relates to friction and torque, On Earth we do have to consider the atmosphere. But it this is highly variable depending on what it actually is. Shape, mass etc...This is the only difference as it relates to a vacuum, the only thing. You can make it negligible, depending on what it is swinging.

Keeping in mind that weight is different to mass. A Bowling ball and banana will still fall at the same speed. There is also the distribution of mass and center of mass to consider.

Low gravity will cause a larger oscillation period as will some of the other things above, friction and the like.

You can replicate lunar gravity with a simple speed percentage factor of around 246% or inversely around 41% because the constant is a... well constant.
 
It is hard to discern a relevant point in all of that, LoneShaman - especially one which is also correct. Perhaps you ought to have waited until you had the time to construct a meaningful response, especially after having had the time to actually read the responses so far?

The closest I can come to discerning a relevant point (by implication) is this:

Remember that the force of gravity is downward (for the sake of simplicity). Gravity will want to align whatever in this direction.

It seems that with this you are suggesting (rather: continuing to suggest) that gravity saps a pendulum of energy and causes it to slow down and tend towards a stable, still, central position, and that you are thereby contesting the claim made by Bart and myself that a(n already swinging) frictionless pendulum in a vacuum is in a state of perpetual motion. To reiterate: you are emphatically wrong about this.

OK, OK - ask a bunch of clever physicists about this and they will come up with a few esoteric processes which even in this scenario will dissipate tiny amounts of energy from the swinging pendulum - but this is a minor quibble, and in no way validates your contention with respect to gravity: a contention which is completely unfounded and based on a fundamental misunderstanding of physics. By the way: follow and read that link. It proves that the position that Bart and I have taken is completely (quibbles aside) supported by modern physics.
 
It is hard to discern a relevant point in all of that, LoneShaman - especially one which is also correct. Perhaps you ought to have waited until you had the time to construct a meaningful response, especially after having had the time to actually read the responses so far?

The closest I can come to discerning a relevant point (by implication) is this:



It seems that with this you are suggesting (rather: continuing to suggest) that gravity saps a pendulum of energy and causes it to slow down and tend towards a stable, still, central position, and that you are thereby contesting the claim made by Bart and myself that a(n already swinging) frictionless pendulum in a vacuum is in a state of perpetual motion. To reiterate: you are emphatically wrong about this.

OK, OK - ask a bunch of clever physicists about this and they will come up with a few esoteric processes which even in this scenario will dissipate tiny amounts of energy from the swinging pendulum - but this is a minor quibble, and in no way validates your contention with respect to gravity: a contention which is completely unfounded and based on a fundamental misunderstanding of physics. By the way: follow and read that link. It proves that the position that Bart and I have taken is completely (quibbles aside) supported by modern physics.

OK, Let me try again. let's ignore air resistance (which is a vacuum in this example), and friction as in the hypothetical simple pendulum. (That does not actually exist.)

There are two major forces acting on the pendulum. One is the tension force that is upward toward the pivot point of the pendulum. The other is a restoring force acting directly downward toward the Earth or moon for that matter and is always constant. These forces are not the same, so one of them must be resolved. The tension is always projected towards the pivot point and varies in magnitude. The restoring force is gravity of course. it is constant. It is gravity that is resolved.

Sorry you are wrong.
 
Sorry haven't read all the posts yet, in a rush.
...
Then please answer when you have the time, because this post does not help anyone to understand what you mean. There is no need to rush.
The physics here are quit clear. If you have good physics based objections, simply state them, maybe there are things we havent considered.

This post did not make it clear with what you disagree.
Maybe it is easier if i make some statements, and you can see what you do, or don't, agree with.

1 - To put it simply, a pendulum gains the same amount of energy in the downswing as it loses in the upswing.
So it goes forever if there are no factors that allow it to dissipate energy.

2 - Again, if there are no factors that allow that dissipate energy, gravity does not slow down a pendulum, it is what keeps the oscillation going.

3 - Aerodynamic drag is an important factor in slowing a pendulum down.

4 - the aerodynamic drag on this bag is going to be significant, being hinged at two points, and presenting all of it's surface area perpendicular to the movement.
The fact that, in your explanation, you think this bag can be moved by a puff of air from some vent, means you are well aware of that, something that can be moved by air, can be stopped by air.

5 - friction on the hinge points is another important factor in slowing a pendulum down.

6 - friction is going to be less for lower weight, or said in another way, the same mass in lower gravity.

7 - All other factors being equal, lower gravity is going to result in a longer period, or lower frequentie. in case of moon gravity, almost a 2.5 times longer period.

8 - the longest we see the bag swinging, is a bit less than a minute.

9 - this all means:
One factor of impediment, aerodynamic drag, is completely absent on the moon.
Another, friction, is strongly reduced.
It is hard for me to give an educated guess, but the bag must be swinging, at the very least, one order of magnitude longer than on earth.
my uneducated guess would somewhere between 25 to 100 times.

10 - Given 8 and 9, slow down would not even be noticeable.

So take your time LS, point 9 can be an interesting discussion, but it is a bit premature to start that one with you before we know where you are on the other points.
 
Last edited:
Then please answer when you have the time, because this post does not help anyone to understand what you mean. There is no need to rush.
The physics here are quit clear. If you have good physics based objections, simply state them, maybe there are things we havent considered.

This post did not make it clear with what you disagree.
Maybe it is easier if i make some statements, and you can see what you do, or don't, agree with.

1 - To put it simply, a pendulum gains the same amount of energy in the downswing as it loses in the upswing.
So it goes forever if there are no factors that allow it to dissipate energy.

2 - Again, if there are no factors that allow that dissipate energy, gravity does not slow down a pendulum, it is what keeps the oscillation going.

3 - Aerodynamic drag is an important factor in slowing a pendulum down.

4 - the aerodynamic drag on this bag is going to be significant, being hinged at two points, and presenting all of it's surface area perpendicular to the movement.
The fact that, in your explanation, you think this bag can be moved by a puff of air from some vent, means you are well aware of that, something that can be moved by air, can be stopped by air.

5 - friction on the hinge points is another important factor in slowing a pendulum down.

6 - friction is going to be less for lower weight, or said in another way, the same mass in lower gravity.

7 - All other factors being equal, lower gravity is going to result in a longer period, or lower frequentie. in case of moon gravity, almost a 2.5 times longer period.

8 - the longest we see the bag swinging, is a bit less than a minute.

9 - this all means:
One factor of impediment, aerodynamic drag, is completely absent on the moon.
Another, friction, is strongly reduced.
It is hard for me to give an educated guess, but the bag must be swinging, at the very least, one order of magnitude longer than on earth.
my uneducated guess would somewhere between 25 to 100 times.

10 - Given 8 and 9, slow down would not even be noticeable.

So take your time LS, point 8 can be an interesting discussion, but it is a bit premature to start that one with you before we know where you are on the other points.

You may have missed my last post.
 
You may have missed my last post.
Yes indeed, but it did not help me a bit to understand what you mean.
Why don't you go through these points and state where you disagree, we can start from there.
For future reference, i do not recognize "Sorry you are wrong" as a physics explanation.
 
it does not matter what explanation of what you give on this thread the answer is always "Sorry, you are wrong". This pendulum thread is an example.
I know, the earth is flat, the moon is made of cheese, but i have to earn my lunars somehow, big moon does not pay me for nothing.
 
this post is for Lone Shaman,

kudos for bringing a great thread on line. but Lone, I have to ask you the question that
i have inserted here a couple of times. is the moon artificial? My answer is Yes. what say ye?

everybody knows the answer to that.

mooncheese_hr.0.0.jpg
 
I suspect that this will fall upon deaf ears, as hustle-narratives eschew competence. But here goes anyway... The primary differentiating elements have little to do with pendulum physics - rather it is a matter of the ratio of friction/drag between the same mechanism operating on the Moon and it operating on the Earth. Yes, pendulum effects play into this math, but they do not serve to differentiate a mechanical ratio of entropy - and this is the critical path issue.

Within a normal relevant range of hanging mechanism mechanics, the bag on the Moon would swing 21 to 25 (or more given two mounts in the video reality) times longer than the same bag on the Earth, all things being equal, save for atmosphere and gravity. The fact that there are two mounts here, only serves to make this argument stronger - so we will assume that two mounts can be mathematically equated to one longitudinal axis, below.

The bag did exactly what it should have done on the Moon and exactly what it could never have done on the Earth. This is the same thing with the astronauts bouncing around on the moon - they did exactly what would happen on the Moon and could never have been even near simulated on Earth, by anyone. This is falsifying in its inferential strength.... but somehow, the narrative just repeatedly ignores this.

We have a
- 1 kg mass
- physical pendulum
- bearing load on a fulcrum
- made of two surfaces featuring a combined coefficient of friction of .43, along with an
- aerodynamic drag ratio of bag which is 1.45.


Bag Swining on Moon.png
 
Last edited:
Then please answer when you have the time, because this post does not help anyone to understand what you mean. There is no need to rush.
Yeah it was rushed, it's a mad time for me at the moment. I get that it was a bit cryptic. I am thinking of changing my approach to presenting this issue, in an attempt to avoid the ugliness that results in disagreement. That post was like a bit of laundry list of stuff. I get that, but it was about physics for physics sake.

The physics here are quit clear. If you have good physics based objections, simply state them, maybe there are things we havent considered.
Aparently the physics are not quite clear. I thought I did state them (in my laundry list). I was being a bit cryptic on purpose, dropping clues for fun.

This post did not make it clear with what you disagree.

My communication skills are at times inadeqate. Sometimes I simply suggest things rather than say them out right. I did think I had made some things clear though.

That a pendulum in a vacuum has negligible difference to ones here on Earth. It is the same as the gravitational fall speed. For example most household items will all fall at the same rate no matter mass or weight. It's only things that are going to have an obvious affect with the air that are different. There is always a small effect but it really is negligible, that is why most things fall at the same rate.

Maybe it is easier if i make some statements, and you can see what you do, or don't, agree with.

Righto.

1 - To put it simply, a pendulum gains the same amount of energy in the downswing as it loses in the upswing.

So it goes forever if there are no factors that allow it to dissipate energy.
\

No that's not true. I did think I made this clear in my other post. I will try and make it as simple as possible. Like I said there are two primary forces in the case of a simple pendulum. Gravity and Tension. These forces are not equal. So it must resolve to one. Think of it like they have different values so they don't even out and one ends up winning.

The restoring force is gravity. Always constant, and toward the Earth or Moon. The other is tension. Along the pendulum line from the bob to the pivot point. It is not constant it is changing in direction and magnitude. I hope that makes sense. Because of these changes gravity is resolved to eventually bring the pendulum to rest.

2 - Again, if there are no factors that allow that dissipate energy, gravity does not slow down a pendulum, it is what keeps the oscillation going.

That not true. Gravity is the restoring force. The other main factor in restoring a compound pendulum is friction and torque

3 - Aerodynamic drag is an important factor in slowing a pendulum down.

It's a factor no bigger than the difference in fall rates between things. Very little actually, depending on shape and structure of course eg Feather's tissues, you know what I am getting at.

4 - the aerodynamic drag on this bag is going to be significant, being hinged at two points, and presenting all of it's surface area perpendicular to the movement.

More friction because of the two hooks, counting them as one would be halving the friction of course, one of the major contributors to slowing the pendulum. and the material of the straps. But pretty insignificant to drag, about the same as the difference in dropping a bowling ball and a utility bag full of equipment. This is self evident.

The fact that, in your explanation, you think this bag can be moved by a puff of air from some vent, means you are well aware of that, something that can be moved by air, can be stopped by air.

As above.

5 - friction on the hinge points is another important factor in slowing a pendulum down.

True.

6 - friction is going to be less for lower weight, or said in another way, the same mass in lower gravity.

True but there are other things to consider, there is a large range of variables here.

7 - All other factors being equal, lower gravity is going to result in a longer period, or lower frequentie. in case of moon gravity, almost a 2.5 times longer period.

A longer period of oscillation, Same number of oscillation though. Basically yes. That is pretty accurate for the estimation of a longer period (see below). Well done. The atmospheric drag is quite negligible, gravity is the only thing different. The major player. It is scalable. Remember force is proportional to mass. You would see pretty much the same reduction at the oscillation count, but not time.

8 - the longest we see the bag swinging, is a bit less than a minute.

As i said before, it is up to you to decide. I see no change at all. Do not think of those little office pendulums as a accurate piratical example. There are so many variables in play here, none that are working towards that type of model.

9 - this all means:

One factor of impediment, aerodynamic drag, is completely absent on the moon.

That impediment is negligible. Compare fall rates for example.

Another, friction, is strongly reduced.

Reduced but highly variable depending on the mass of the bag and equipment in it, it's distribution, and compounded by the two straps and structure

It is hard for me to give an educated guess, but the bag must be swinging, at the very least, one order of magnitude longer than on earth.

The oscillation period is about 2.9 seconds, On Earth this would be about 1.2 seconds with some small added time do to the adjustment of friction as you mention. This is both back and forth.

my uneducated guess would somewhere between 25 to 100 times.

You can simulate lunar fall rates to Earth or vice versa as a percentage. Approximately %246 or inversely aprox %41.
10 - Given 8 and 9, slow down would not even be noticeable.

Like I said I am changing my approach as I don't enjoy the ugliness that has already happened in the thread. I don't want to have to argue about everything that is selected as a argument point. By all means correct me I f I am wrong, but we all have our own minds. So it is up to the individual to decide. I do believe there should be at least some noticeable reduction in speed, or even a very noticeable reduction given the various other conditions.

So take your time LS, point 8 can be an interesting discussion, but it is a bit premature to start that one with you before we know where you are on the other points.

Yeah that did take some time, Phew. Yes it is interesting purely on physics alone. But please understand, I left the forum last time because I did not approach the subject well. It was going to recur in the same fashion. I accept responsibility for this. So we can use this as a fun exercise and not let it turn into a war. I respect your opinion. I would ask however to keep at least a tiny window in your mind that some things, nearly all things IMO are not quite on the level,or as they have been presented.

Cool?
 
Last edited:
There are two major forces acting on the pendulum. One is the tension force that is upward toward the pivot point of the pendulum. The other is a restoring force acting directly downward toward the Earth or moon for that matter and is always constant.

So far, so good. These are indeed the two major forces, as you describe them. The problem comes with your understanding of how they are resolved:

These forces are not the same, so one of them must be resolved. The tension is always projected towards the pivot point and varies in magnitude. The restoring force is gravity of course. it is constant. It is gravity that is resolved.

Whilst you are correct that tension is always directed toward the pivot point, and that it varies in magnitude, the rest of what you say is very vague, and it is not entirely clear to me how you intend the forces to be "resolved". Here, though, is how I have been taught to resolve these forces:

When multiple forces are acting upon a body, they can be represented as vectors ("arrows" of force with both magnitude and direction, where the greater the magnitude, the longer the arrow). The total effective force then - the resultant force which ultimately acts upon the body as though the body were subject to only a single force - is determined by summing up all of these vectors, which in visual terms amounts to placing them all head-to-tail and drawing a final vector from the tail of the first to the head of the last.

Here's how this works for a pendulum. First, let's identify the force vectors (I have "borrowed" the first diagram from these lecture notes, which I otherwise haven't read, but they do look informative):

screenshot-forces-on-pendulum.png
Here, the two vectors for the forces of gravity (mg) and tension (T) are shown, along with the effective force that this results in, Fnet. Here, as I described above, is how we arrive at that Fnet vector (I mocked this image up myself based on the above, and pretty roughly):

pendulum-force-vectors-resolution.png
Here, we start by laying out the gravity vector, mg. Then, we place the tail of the tension vector, T, at the head of the gravity vector, and, to arrive at the effective resultant force - to "resolve" the forces as you put it - we sum these vectors by drawing a new vector from the tail of the gravity vector to the head of the tension vector.

Note that Fnet is on a tangent to the arc of the pendulum's swing at this point in its swing. In other words, at all times, the effective force on the pendulum acts along its arc. [Edit: My physics is a little rusty. I got this slightly wrong, as acknowledged in this later post. The effective force points slightly upwards from the tangent, because as well as accelerating the pendulum along the tangent, it has to accelerate it upwards to change the tangent (centripetal force).] This can be proven, but for brevity and efficient use of energy I won't do that in this post.

What is the upshot of this? How does it relate to the competing claims in this thread?

It demonstrates that the effect of gravity - on the pendulum's downward motion - is, when the force of tension is also taken into account, to resolve into a force which accelerates the pendulum along its arc. The exact opposite is the case during the pendulum's upward motion. Gravity again resolves into a force along the pendulum's arc, but this time to decelerate it (you can again draw a very similar diagram as the above which shows this). Here's the key point though: although the directions of these forces are opposite, the magnitudes of the forces at the opposite points in its arc are identical. In other words, the overall acceleration due to gravity (when resolved with tension) is identical to the overall deceleration due to gravity.

This is why gravity does not act to slow down the pendulum or dissipate its energy: the forces it exerts upon the pendulum over an entire oscillation (when resolved with the tension) are equally balanced.

Sorry you are wrong.

I'm not, but I'm open to your explanation as to how you think I am. Nothing that I've explained above would be at all controversial in a high school physics class (which I took).
 
Last edited:
The ETB has not reduced by a single pixel! Over a duration of approximately 49.5 seconds, Gravity, friction, torque has had no effect what so ever.

ETB-bagGif.gif
 
Last edited:
Gravity, friction, torque has had no effect what so ever.

As I explained above: gravity isn't expected to have any effect. As for torque, that's the resultant force (Fnet in my diagrams above), and, like gravity, its effects are symmetric about the axis of the pendulum's swing, so it, too, is not expected to have any effect. [Edit: Boy, my physics really is rusty. I'd forgotten that torque is not a force but the moment of a force, that is, the force multiplied by its distance from the focal point. So the torque in this scenario is Fnet x L, with L being the length of the pendulum.]

As for friction: I quoted from Wikipedia that it is roughly 1% of the combined forces of friction and air resistance on Earth, so it is not expected to have very much effect at all.

You are not showing us anything that is beyond the bounds of expectation.
 
Last edited:
Back
Top