Explanation: If you drop a hammer and a feather together, which reaches the ground first? On the Earth, it's the hammer, but is the reason only because of air resistance? Scientists even before Galileo have pondered and tested this simple experiment and felt that without air resistance, all objects would fall the same way. Galileo tested this principle himself and noted that two heavy balls of different masses reached the ground simultaneously, although many historians are skeptical that he did this experiment from Italy's Leaning Tower of Pisa as folklore suggests. A good place free of air resistance to test this equivalence principle is Earth's Moon, and so in 1971, Apollo 15 astronaut David Scott dropped both a hammer and a feather together toward the surface of the Moon. Sure enough, just as scientists including Galileo and Einstein would have predicted, they reached the lunar surface at the same time. The demonstrated equivalence principle states that the acceleration an object feels due to gravity does not depend on its mass, density, composition, color, shape, or anything else. The equivalence principle is so important to modern physics that its depth and reach are still being debated and tested even today.
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 4:23 am
by Beyond
Has that ever been tried in a really big vacuum chamber on earth?
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 4:29 am
by Wolf kotenberg
I saw that real time
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 4:57 am
by bystander
Beyond wrote:Has that ever been tried in a really big vacuum chamber on earth?
Do you think the result would be different?
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 5:09 am
by Caetano J.
bystander wrote:
Beyond wrote:Has that ever been tried in a really big vacuum chamber on earth?
Do you think the result would be different?
I think he's suggesting it would be a more controllable environment, leading to more precise results. But i'll bet that was done even before the Apollos, and that the "hammer versus feather" experiment was more of a show to raise scientific interest
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 5:37 am
by Beyond
Caetano J. wrote:
bystander wrote:
Beyond wrote:Has that ever been tried in a really big vacuum chamber on earth?
Do you think the result would be different?
I think he's suggesting it would be a more controllable environment, leading to more precise results. But i'll bet that was done even before the Apollos, and that the "hammer versus feather" experiment was more of a show to raise scientific interest
Actually, i was curious if they knew first hand before they went to the moon. Either way, it made for very good PR. Especially to the masses, who most likely had no idea of that at all.
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 5:41 am
by Giordano Bruno
Supposedly on the Moon , Scott drops the feather and the hammer while Irwin is seen moving around . The question is : who is holding and operating the movie camera ???
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 5:47 am
by iamlucky13
Giordano Bruno wrote:Supposedly on the Moon , Scott drops the feather and the hammer while Irwin is seen moving around . The question is : who is holding and operating the movie camera ???
There's still debate to this day if it was on a tripod, or if Marvin the Martian happened to be trying to blow up the moon that day and they convinced him to work the camera in exchange for a hint where his Aludium Q-36 explosive space detonator might be.
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 7:46 am
by Guest
acceleration an object feels due to gravity does not depend on its mass, density, composition, color, shape, or anything else.
Are you sure? Red cars go faster and accelerate faster than identical cars of any other colour. Has anyone tried simultaneously dropping a red hammer and another coloured hammer on the Moon or a vacuum chamber? No speculation, please. Give me empirical data or nothing.
Sven.
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 8:34 am
by montylc2001
i watched this live as a youngster, and never doubted the results
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 9:28 am
by Maggie M'Gill
I just wish Obama hadn't cancelled Constellation...
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 11:06 am
by Dr C
Objects "experience" an acceleration, they "feel" forces. Words matter!
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 11:17 am
by 7U_D4
Beyond wrote:Has that ever been tried in a really big vacuum chamber on earth?
Yes, but always released electromechanically rather than by a space-suited human hand.
I also recall watching this unfold live as a teen about to enter my Freshman year (high school). Just seeing the image brought to mind the voice of Commander Scott over the crackly radio. I was born under a Sputnik sky and the space program was a great adventure to watch as a child. It lead me to a career starting in the solid rockets and then for a few years at the Boeing Defense & Space Group before moving on to energy research. While at Boeing I worked on a project simulating splashdown of manned space capsules similar to the Apollo for the ISS. I found many of the old Apollo era documents in the library. It is amazing what that generation of engineers were able to accomplish with the tools of the time, but it is certain that they did in fact do it.
What struck me as un-natural watching the video was the acceleration of the dropped objects compared to normal experience on earth. Of course it makes sense since the acceleration of gravity on the moon is only 1/6 that we are accustomed to on earth. This was not mentioned in the clip or the written description but is interesting nonetheless.
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 11:35 am
by DanaP
Actually...
The hammer still hits the ground first on the moon. The difference is INCREDIBLY small, but it does hit first. Why? Gravity is a MUTUAL force. You forget that even as the hammer falls toward the moon, so the moon falls toward the hammer. The hammer's mass vastly outweighs the feather. So the moon falls toward the hammer much faster than towards the feather. You'd need a high speed camera with micrometer resolution and very precise handling to see it. However, it is true.
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 11:50 am
by rstevenson
DanaP wrote:Actually...
The hammer still hits the ground first on the moon. The difference is INCREDIBLY small, but it does hit first. Why? Gravity is a MUTUAL force. You forget that even as the hammer falls toward the moon, so the moon falls toward the hammer. The hammer's mass vastly outweighs the feather. So the moon falls toward the hammer much faster than towards the feather. You'd need a high speed camera with micrometer resolution and very precise handling to see it. However, it is true.
Are you suggesting that the portion of the moon directly below the hammer will heave up just a touch above the portion of the moon directly below the feather? If not, then how is this greater attraction supposed to manifest itself?
Rob
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 11:51 am
by rstevenson
Guest wrote:
acceleration an object feels due to gravity does not depend on its mass, density, composition, color, shape, or anything else.
Are you sure? Red cars go faster and accelerate faster than identical cars of any other colour. Has anyone tried simultaneously dropping a red hammer and another coloured hammer on the Moon or a vacuum chamber? No speculation, please. Give me empirical data or nothing.
Sven.
I suspect that no amount of empirical evidence would satisfy someone who believes that "Red cars go faster and accelerate faster than identical cars of any other colour."
Rob
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 11:56 am
by 7U_D4
DanaP wrote:Actually...
The hammer still hits the ground first on the moon. The difference is INCREDIBLY small, but it does hit first. Why? Gravity is a MUTUAL force. You forget that even as the hammer falls toward the moon, so the moon falls toward the hammer. The hammer's mass vastly outweighs the feather. So the moon falls toward the hammer much faster than towards the feather. You'd need a high speed camera with micrometer resolution and very precise handling to see it. However, it is true.
But if the moon falls toward the hammer it also falls toward the feather at the same rate since they are side by side and released at the same time. So the impact would still be at the same time assuming instantaneous release and identical length.
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 12:30 pm
by neufer
7U_D4 wrote:
Beyond wrote:
Has that ever been tried in a really big vacuum chamber on earth?
Yes, but always released electromechanically rather than by a space-suited human hand.
Seldom with a hammer for some reason.
Click to play embedded YouTube video.
Click to play embedded YouTube video.
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 12:56 pm
by Questions?
Imagine, another unanswered question.
When will we actually read about things that NASA knows?
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 1:42 pm
by owlice
Guest wrote:
acceleration an object feels due to gravity does not depend on its mass, density, composition, color, shape, or anything else.
Are you sure? Red cars go faster and accelerate faster than identical cars of any other colour. Has anyone tried simultaneously dropping a red hammer and another coloured hammer on the Moon or a vacuum chamber? No speculation, please. Give me empirical data or nothing.
Sven.
rstevenson wrote:I suspect that no amount of empirical evidence would satisfy someone who believes that "Red cars go faster and accelerate faster than identical cars of any other colour."
Rob
I suspect Sven is familiar with the rate at which red cars get speeding tickets, as opposed to cars of all other colors. This is why I drive a silver car. (And a study has shown that silver cars are involved in fewer accidents than cars of other colors.)
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 2:24 pm
by JohnD
Now I'm no Moon Conspiracist, but that was weird.
At least two zoom adjustments during that clip - I assumed by the astronaut behind the camera.
And then he appears from stage right! At the same distance from the camera as Astronaut Scott.
Was the camera being adjusted remotely, from Earth?
What about the time delay?
John
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
Posted: Tue Nov 01, 2011 3:12 pm
by neufer
rstevenson wrote:
DanaP wrote:
The hammer still hits the ground first on the moon. The difference is INCREDIBLY small, but it does hit first. Why? Gravity is a MUTUAL force. You forget that even as the hammer falls toward the moon, so the moon falls toward the hammer. The hammer's mass vastly outweighs the feather. So the moon falls toward the hammer much faster than towards the feather. You'd need a high speed camera with micrometer resolution and very precise handling to see it. However, it is true.
Are you suggesting that the portion of the moon directly below the hammer will heave up just a touch above the portion of the moon directly below the feather? If not, then how is this greater attraction supposed to manifest itself?
Even if this wasn't the case the solar photon pressure pushing the feather downward produces feather accelerations that are some 15 orders of magnitude greater than the acceleration of the moon being pulled upward (by it's attraction to the hammer).
Re: APOD: Hammer Versus Feather on the Moon (2011 Nov 01)
JohnD wrote:
Now I'm no Moon Conspiracist, but that was weird.
At least two zoom adjustments during that clip - I assumed by the astronaut behind the camera.
And then he appears from stage right! At the same distance from the camera as Astronaut Scott.
Was the camera being adjusted remotely, from Earth?
Hammer Versus Feather on the Moon
(And a 
