The Greatest Physics Demo of All Time Happened on the Moon (wired.com) 112
This true story of a hammer, a feather, the Apollo 15 mission, and the answers to humanity's oldest questions about how stuff falls. From a report: Does a falling object move at a constant speed, or does it speed up? If you drop a heavy object and a light one at the same time, which will fall faster? The great thing about these two questions is that you can ask pretty much anyone and they will have an answer -- even if they are actually wrong. The even greater thing is that it's fairly simple to determine the answers experimentally. [...] OK, but what about dropping a rock and feather -- doesn't the rock hit first? Usually, the answer is yes. But let's replace the rock with a hammer and then just take a change of scenery and move the experiment to the moon. This is exactly what happened during the Apollo 15 lunar mission in 1971. Commander David Scott took a hammer and an eagle feather and dropped them onto the lunar regolith. Here's what happened: The feather and the hammer hit the ground at the same time.
Why did it happen? First, it is indeed true that even on the moon there is a greater gravitational force on the hammer than the feather. We can calculate this gravitational force as the product of mass (m in kilograms) and the gravitational field (g in newtons per kilogram). On the surface of the moon, the gravitational field has a value of 1.6 N/kg. If you put this expression in for the net force on a falling object, it looks like this: Fnet = - mg = ma; a = -g. Since both the gravitational force and the acceleration depend on the same mass, it's on both sides of the equation and cancels. That leaves an acceleration of -g. The hammer and the feather fall down with identical motions and hit the ground at the same time.
So, what's different about dropping something on the moon versus on Earth? Yes, there is a different gravitational weight on the moon -- but that's not the issue. It's the lack of air that makes the difference. Remember that Newton's second law is a relationship between the net force and the acceleration. If you drop a feather on the surface of the Earth, there are two forces acting on it. First, there is the downward-pulling gravitational force that is equal to the product of mass and the gravitational field. Second, there is an upward-pushing force due to the interaction with the air, which we often call air drag. This air drag force depends on several things, but the important ones are the object's speed and the size of the object. [...]
Why did it happen? First, it is indeed true that even on the moon there is a greater gravitational force on the hammer than the feather. We can calculate this gravitational force as the product of mass (m in kilograms) and the gravitational field (g in newtons per kilogram). On the surface of the moon, the gravitational field has a value of 1.6 N/kg. If you put this expression in for the net force on a falling object, it looks like this: Fnet = - mg = ma; a = -g. Since both the gravitational force and the acceleration depend on the same mass, it's on both sides of the equation and cancels. That leaves an acceleration of -g. The hammer and the feather fall down with identical motions and hit the ground at the same time.
So, what's different about dropping something on the moon versus on Earth? Yes, there is a different gravitational weight on the moon -- but that's not the issue. It's the lack of air that makes the difference. Remember that Newton's second law is a relationship between the net force and the acceleration. If you drop a feather on the surface of the Earth, there are two forces acting on it. First, there is the downward-pulling gravitational force that is equal to the product of mass and the gravitational field. Second, there is an upward-pushing force due to the interaction with the air, which we often call air drag. This air drag force depends on several things, but the important ones are the object's speed and the size of the object. [...]
High school physics now? (Score:5, Insightful)
So /. has degenerated into basic high school physics now?
What, not enough cryptocurrency articles to shill today?
Re:High school physics now? (Score:5, Interesting)
It was a dramatic demonstrated, although not terribly informative. I took on gravity for a science project assignment in elementary school. Ramps, a stopwatch, my Mom's bowling ball, a whiffle ball, and a softball.
What, not enough cryptocurrency articles to shill today?
Let us count our blessings.
Re: High school physics now? (Score:5, Insightful)
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The greatest physics demo of all time was getting them there in the first place.
Nope. That would be "engineering". Rocketry was not experimental at that time. Scaling it up to this was.
Re: High school physics now? (Score:2)
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The greatest physics demo of all time was getting them there in the first place.
Nope. That would be "engineering". Rocketry was not experimental at that time. Scaling it up to this was.
I highly doubt it was all engineering. Getting to the moon was VERY experimental at that time.
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The greatest physics demo of all time was getting them there in the first place.
Nope. That would be "engineering". Rocketry was not experimental at that time. Scaling it up to this was.
I highly doubt it was all engineering. Getting to the moon was VERY experimental at that time.
It is called "experimental engineering". Still engineering.
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Sure, the science behind rocketry was all done. No need for astrophysicists, right? Seriously?
Re: High school physics now? (Score:2)
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It was a dramatic demonstrated, although not terribly informative. I took on gravity for a science project assignment in elementary school. Ramps, a stopwatch, my Mom's bowling ball, a whiffle ball, and a softball.
What, not enough cryptocurrency articles to shill today?
Let us count our blessings.
...on the blockchain.
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Sounds great, let me just right click that [imgur.com].
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Well at least this video should put to bed the conspiracy theory we never put men on the moon and it was all staged. They didn't put these guys into a huge vacuum to be able to do this demo.
Re:High school physics now? (Score:4, Informative)
https://en.wikipedia.org/wiki/... [wikipedia.org]
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Unfortunately there is no amount of facts that will convince fundamentalists. There are multiple proofs that the earth is spherical shaped but conspiracy theorists are stuck in denial. There is a reason we have that joke: "Da Nile is not just a river in Egypt."
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They don't really want to be convinced. Their brain is rewarded (mostly with attention) for not believing that the moon landing happened.
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Indeed. Intellectually they are basically stuck at the development stage of children that think their fantasy will be true if they just believe hard enough. Children eventually learn that by running against a wall they only hurt themselves. The smarter ones figure out this is a general principle. The fundamentalists and reality deniers never figure that out and think they just need to run harder against that wall.
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Is there a way to mod something both +1 Funny and +1 Sad at the same time?
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Naa. Probably just CGI from the Quantum Computer the NSA already had back then...
High school hammer $5 NASA one $5M (Score:1)
High school hammer $5 NASA one $5M
Re:High school hammer $5 NASA one $5M (Score:5, Funny)
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Price: $5
Shipping and handling: $4,999,999,995
Re:High school physics now? (Score:5, Interesting)
So /. has degenerated into basic high school physics now?
It's shocking how uneducated people are.
I teach an upper-year philosophy of science course at university, and it is scary how many of my students think that a pen, say, hits the ground before a piece of paper because the pen is "heavier." Most students in fact do think this.
But I don't need the moon. I take a piece of paper, crumple it up, and drop it simultaneously with the pen.
Then I say: too bad Aristotle never though to crumple paper up.
Re: High school physics now? (Score:2)
Bill Nye should be required viewing for kids. I learned this long before my first science or physics classes.
Re: High school physics now? (Score:2)
I grew up on 321 Contact and other random PBS science shows.
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Weight does have some to do with it. A sheet of metal will fall faster than a sheet of paper (in air of course)
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Weight does have some to do with it. A sheet of metal will fall faster than a sheet of paper (in air of course)
It has something to do with the air drag equation, yup. Nothing to do with the gravitational equation. Which is why people are so easily confused on the subject in the first place.
It's long been said that fish don't have a word for water, as an allegory to describe this myopia in the human mind. Most everybody simply takes air for granted, and has to exert specific effort to remember that air pressure matters when things fall.
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I think the failure to teach philosophy in the US in primary and secondary education is partially to blame for this. Students are taught what to think instead of how to think.
Agreed. The problem, of course, is that it's far easier to test "what to think", rather than "how to think". Math is pretty easy to test consistently, but gauging whether a student knows "how to think" is far more difficult to assess, which means it's more difficult to grade.
This is compounded by the fact that teachers are flawed people as well. A student who presents an answer which reflects independent thought but is contrary to the beliefs of the teacher is more likely than not to be graded more harshly
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I think (...) this is what you are saying, but just to underline it: It's one thing to know how to manipulate symbols in algebra, calculus etc., and solve an equation. It's an entirely different thing to know how to set up the equations in the first place so as to model some real-world situation. The example from the article of combining the equation for gravitational attraction of a mass, and the equation for acceleration of a mass, and then showing that the mass cancels out, is a good example. Once the
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Then I say: too bad Aristotle never though to crumple paper up.
Aristotle didn't have paper. He would have had to use parchment or papyrus, neither of which crumple well.
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and it is scary how many of my students think that a pen, say, hits the ground before a piece of paper because the pen is "heavier."
The pen does hit the ground because it's heavier. In an atmosphere.
Crumple up your ball of paper, and then drop it at the same time as an equally sized ball made of lead.
If you want the best demonstration of the principle, drop a sheet of paper, and a sheet of lead.
Air drag is one side of the equation. The other side is mass.
The moon experiment verified our understanding that gravitational mass == inertial mass.
It didn't prove that atmospheric drag is unaffected by weight.
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So /. has degenerated into basic high school physics now?
High school? Although I didn't know the math, I knew by the time I was in Grade 6 that absent atmosphere the rock and the feather would fall at the same speed.
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You might have known that, but it's doubtful that it was taught to you in any public school...at least in the US in sixth grade.
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So /. has degenerated into basic high school physics now?
It's historically relevant. There wasn't a huge STEM education push back in 1971 - most people likely didn't even know that the hammer and a feather should fall at the same rate. Frankly, I'm not sure what percentage of people are aware of that, even nowadays.
I will say that, as a 10-year-old kid at the time, I thought it was a freaking cool demo. Heck, the whole Apollo program was mind-blowing!
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There in fact WAS a big STEM push back then, although they didn't call it STEM. It came out of the Soviet launch of Sputnik I and II in 1957, and the subsequent failure of the US Vanguard rocket. Although by 1969, the events of the '60s (particularly the Vietnam war and the hippies movement) had helped to put some tarnish on that model.
Re: High school physics now? (Score:2)
High School? I was think Elementary School.
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The article is dumb, but the video is pretty cool [youtube.com]. I wish we had more of this kind of stuff.
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So /. has degenerated into basic high school physics now?
What, not enough cryptocurrency articles to shill today?
The morons need something to make them think they understand some things. This is probably "advanced" Science for them, as it involves rockets.
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Love your reply. Bravo!
Deep (Score:2)
So great that Slashdot is exploring the depths of high school physics.
Apollo....scofflaws (Score:5, Funny)
Per the Bald and Golden Eagle Protection Act of 1940, possession of feathers of any migratory bird other than the pigeon, starling or house sparrow is illegal.
Apparently Mr Scott didn't learn from the postal covers incident?
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Loophole: It wasn't a bald eagle until Kubrick plucked its feather.
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The feather was from falcon that was one of the mascots of the Air Force Academy in Colorado Springs, so not from a migratory bird but a legal pet. It's very hard to get permits to have a falcon as a pet, but the USAF does it.
https://www.atlasobscura.com/a... [atlasobscura.com]
"Demo", not "experiment" (Score:1, Flamebait)
This is demonstrating Physics for the masses, i.e. a "show". Nobody with a solid understanding of Physics needed that demo. It was not an real experiment either as it contributed nothing to make the established part of Physics more solidly founded.
Now, if the Demo had failed, that would have made it an actual experiment and have been extraordinary evidence and some very basics Physics would have gotten revisited. But it did not.
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experiment /ikspermnt/
noun
a scientific procedure undertaken to make a discovery, test a hypothesis, or demonstrate a known fact.
Highschool physics? (Score:3, Funny)
Re: Highschool physics? (Score:5, Funny)
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Heheheh, excellent!
Slashdot (Score:5, Funny)
News for people who never did physics in their first year of highschool.
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Next we'll be getting articles on the perils of the most dangerous chemical of all time, dihydrogen monoxide.
"Fallen Astronaut" - the only artwork on the Moon (Score:1)
"Does a falling object move at a constant speed" (Score:2)
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I think we can prove objectively that objects cannot change speed.
First, imagine that to change from starting speed to final speed, you have to change your speed halfway to the final speed.
Then imagine that to change from starting speed to halfway, you have to change your speed to half of that.
Etc, etc, never-ending. Thus you can never get any initial speed, and changing speed is impossible. It's logical.
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That makes sense, since changing speed is impossible.
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In a universe where speed can only be set by half increments of some other number, what you say is true.
Fortunately, we don't live in such a universe.
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It doesn't matter, setting speed to any other fractional portion will give the same result.
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You're setting a stipulation that you must traverse specific fractional amounts, and only fractional amounts.
This is physically nonsensical- your thought experiment as based on incorrect assumptions.
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First, imagine that to change from starting speed to final speed, you have to change your speed halfway to the final speed.
is false.
Logic based on a false premise is fallacious.
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This is nonsense.
Are you sure?
You're setting a stipulation that you must traverse specific fractional amounts, and only fractional amounts.
No, I'm stating that smaller amounts must be traversed before larger amounts can be. If you are going from 0 to 10 MPH, then you must reach the speed of 5 MPH before you get to 10 MPH.
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Are you sure?
I am completely sure.
It's Zeno's Dichotomy paradox.
The resolution to the paradox is 2-fold:
1) it sets non-physical stipulations
2) it's mathematically incorrect
No, I'm stating that smaller amounts must be traversed before larger amounts can be. If you are going from 0 to 10 MPH, then you must reach the speed of 5 MPH before you get to 10 MPH.
You must pass the speed of 5MPH. There's no requirement that you go 5MPH. This is also covered in Zeno's arrow paradox, which also covers impossibility of motion. It, like the Dichotomy paradox, is also fallacious.
Speed = Distance * Time. No matter the distance, the relationship is set in stone in that relationship.
If my speed is 5 miles per hou
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The point of Zeno's thought experiment isn't to show that motion is impossible, but rather to show that logic is flawed.
1/1 + 1/2 + 1/4 + 1/8 + 1/16 ... = 2.
This is based on the concept of limits, which shows that the sum approaches arbitrarily close to 2, but it doesn't say whether the sum is actually 2 or not.
It's non-physical, because it makes the presumption that reality exists in a state of stop-motion
I don't see why you think it makes this assumption.
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The point of Zeno's thought experiment isn't to show that motion is impossible, but rather to show that logic is flawed.
That's... pretty debatable.
Zeno was a firm believer in the unrealness of concepts such as motion and... well most of reality, really.
His paradoxes are exactly what they seem: Attempts at proving his stoicism correct.
This is based on the concept of limits, which shows that the sum approaches arbitrarily close to 2, but it doesn't say whether the sum is actually 2 or not.
Yes, it is based on the concept of limits.
And yes, it does approach arbitrarily close to 2. Which means the summation is 2.
This is what Cauchy's proof tells us.
For any arbitrarily small denominator, there is also an arbitrarily large numerator. If the sequence converges on a number, the sum
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Hey Zeno, why don't you prove that time never passes, using that same argument.
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Absolutely, done [existentialcomics.com]. Or maybe you prefer this one [existentialcomics.com].
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LOL what, are you going to suggest calculus solves the problem? You're wrong, calculus only answers the question of what happens as you approach the limit, it doesn't say what happens at the limit.
I may not understand this, but you certainly don't.
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Calculus very easily answers whether or not your infinite series diverges, or converges.
Obviously, it converges at your target speed.
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On the moon? Greatest demo? (Score:2)
This is a standard physics experiment that you can go witness yourself at any local science centre. No need to go to the moon, you can build a vacuum chamber in your garage if you want.
Screw the hyperbole, I personally think that the many experiments demonstrated by NASA and ESS scientists on the ISS are far greater. E.g. the effect of gyroscopic stability demonstrated in zero g: https://www.esa.int/ESA_Multim... [esa.int]
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Here's an idea, find out how many local science centers included the demonstration prior to the Apollo 15 mission, and how many decided to include it as a result of the popularity of the Apollo 15 mission. Bonus points for new science centers that were created as a result of the Apollo 15 mission. These are entirely man-made events, you can determine causation in addition to
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Gee, I wonder what event caused so many local science centers to include demonstrations of this experiment.
Galileo dropping differently weighted objects back in the 1500s. That was the event. Or do you think science centres only show experiments which happen on the moon? Please don't be so self important.
Kind of backfired (Score:2)
I remember watching it as a kid, and thinking that the 1/6th G simply made the hammer fall like a feather, the feather's fall looking kind of normal.
What's dramatic was shown to me years earlier, where they dropped a little feather in a air-removed plastic tube, in a 16mm-film we were shown in science class; it dropped like a ball bearing, and they had a twin feather dropped beside the tube.
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I think you left off your tag, because you can't really be that stupid.
Well, not exactly. (Score:5, Informative)
You see, you're neglecting the fact that the moon is also pulled towards the hammer and the feather, and this acceleration is NOT equal.
It is so small an acceleration that you can neglect it for most purposes (the error in precise distance from the moon and the error in the precise time of release will so vastly exceed the difference due to the acceleration of the moon that this sort of experiment cannot show that objects always fall to a common centre, the objects are sufficiently close that the moon is essentially pulled towards both and therefore that acceleration DOES cancel out, and there simply isn't a clock yet built that would be capable of accurately and reliably measuring the difference in time of impact anyway).
So for all experimental purposes, yes, if you release two very small objects in close proximity to each other, this experiment WILL produce the expected result.
However, if you took two objects of sufficient difference in mass sufficiently far away, holding them sufficiently far apart that the acceleration of the moon isn't in the same direction to within the accuracy of measurement, and then released them, you'd be able to use a quantum gas clock to measure the precise difference in time of impact. (We're still assuming objects whose mass is very small compared to that of the moon.)
Or, at least, you would if it weren't for relativity. In physics, the relativity of simultaneity is the concept that distant simultaneity – whether two spatially separated events occur at the same time – is not absolute, but depends on the observer's reference frame. Which means you can't be sure that the two objects were released at the same time or hit at the same time, at least at the sorts of level of precision we're talking about.
So the classic experiment is only valid when the errors in measurement exceed the motion of the larger body, which is going to be so near 100% of the time for any realistic experiment that you can regard it as valid 100% of the time.
The reason for caring about the common centre is that then you have a rule that works all of the time for any arbitrary three masses, regardless of how large they are relative to each other, rather than a simplification that only works because it's impossible to measure the difference. Working with "good enough" approximations is how you perform calculations you can actually use in the real world, it just doesn't let you understand the real world OR why the approximation works.
So the approximation is the very reason so many people struggle with it. It gets you the right results, but for the wrong reason.
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I had the same thought. Imagine that the hammer and the feather were on opposite sides of the moon, and still equal distance from the moon compared to each other. They'll hit the moon at the same time if released at the same time. But if you scale up the distances and also scale up the hammer to be half the size of the moon, then dropping the hammer and the feather at the same time will cause the hammer to pull the moon towards itself a material amount and cause the hammer to hit the moon before the feather
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"The reason for caring about the common centre is that then you have a rule that works all of the time for any arbitrary three masses,"
wait, you solved the general three body problem? Nobel for you!
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No, it does not "solve" the three body problem. Do try to read. I'm sure you're capable. It's trivial to write down the equations for three bodies, there's nothing new here. If you had bothered to get the fuck off your lazy backside, you'd know that. But you'd rather bitch, troll and abuse. Get the FUCK out of my way.
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you are correct, there is nothing new here. which it appears, you fail to realize.
Now take another eight paragraphs to say nothing again. Or you prefer attacking ("do try", "fuck", "lazy", "bitch", "FUCK", "out of my way"- well aren't we important!).
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That's your fantasy and has nothing to do with my post. Go fantasize somewhere else.
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I'm surprised you didn't mention that the hammer and feather attract each other, too. That technically makes it a three-body problem.
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Yes, unfortunately this means that you have to measure with infinite precision and take infinitely small steps in order to get an exact answer.
(The equations can be written down but not solved as they're sensitive to initial conditions. There is no relationship between any initial error and any final error.)
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I think we could actually experimentally show this in space using three objects which vary in mass from one another, but that aren't at such an extreme ratio as the Moon to a hammer. Perhaps use a bowling ball, a baseball, and a ping pong ball. I seem to recall hearing that two baseballs placed one meter apart in orbit will come together and touch in about an hour. So this could possibly be done over a short enough time frame and distance to avoid the complications of managing something on a much larger sca
Fake News... (Score:3)
Everybody knows the moon landings were filmed on a stage in the Arizona desert.
Freshman physics demo... (Score:2)
I saw a similar demo in freshman physics, all those years ago. It use a feather, a penny, a glass tube with a valve at one end and a vacuum pump. At the beginning of the hour, the instructor loaded up the tube, and showed us the usual result. He then hooked it all to the vacuum pump, and started pumping it down while he lectured. Near the end of the hour, after the pump had had time to establish a decent vacuum in the tube, he closed the valve, disconnected the pump, and did it again - and the feather a
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I saw that in school. Pretty impressive.
LIGO was much more awesome (Score:2)
demonstrating a fundamental property of space time.
That was magnificent! https://en.wikipedia.org/wiki/... [wikipedia.org]
Galileo would like a word (Score:2)
In particular he would like to draw your attention to the Leaning Tower of Pisa....
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About a century before the first artificial vacuum I think.
News (Score:2)
Great we are catching on upto date news. I wonder who will win the next presidential election, Nixon or McGovern?
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The real question is whether the R candidate will be Donald or Ivanka.
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Connection to General Relativity (Score:2)
There is a deeper interpretation of this demo/experiment that no one has pointed out yet. As mentioned in the summary and TFA, the hammer and feather fall at the same rate because "both the gravitational force and the acceleration depend on the same mass". But the equivalence of gravitational mass (in the gravitational force equation) and inertial mass (in the acceleration equation) is only a coincidence in Newtonian physics -- there is no reason for it; it's just an observational fact. But in General Re
Now do cats and buttered bread... (Score:2)
Cats always land on their feet, buttered bread always lands on the side with butter.
Is that true in a vacuum as well?
Is that true at lower gravities?
And does a cat/bread pendulum exist on these conditions?
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Is that true in a vacuum as well?
Cats don't survive the vacuum and land randomly. Or the spacesuits impede their twisting abilities. Similar result.
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Next question for these people: Is the Moon made of iron, or green cheese?