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Astronomy Picture of the Day -- Hammer Versus Feather on the Moon
NASA ^ | November 01, 2011 | (see photo credit)

Posted on 11/02/2011 3:14:29 PM PDT by SunkenCiv

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.

November 01, 2011

(Excerpt) Read more at 129.164.179.22 ...


TOPICS: Astronomy; Astronomy Picture of the Day; Science
KEYWORDS: apod; apollo; astronomy; science
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[Credit: Apollo 15 Crew, NASA]

1 posted on 11/02/2011 3:14:39 PM PDT by SunkenCiv
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To: brytlea; cripplecreek; decimon; bigheadfred; KoRn; Grammy; married21; steelyourfaith; Mmogamer; ...

2 posted on 11/02/2011 3:16:59 PM PDT by SunkenCiv (It's never a bad time to FReep this link -- https://secure.freerepublic.com/donate/)
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To: SunkenCiv
Watching "The Universe" last night and I think we need an Amy Mainzer rule for space threads.

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3 posted on 11/02/2011 3:18:48 PM PDT by cripplecreek (A vote for Amnesty is a vote for a permanent Democrat majority. ..Choose well.)
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To: SunkenCiv

We never went to the Moon.

/x-files music


4 posted on 11/02/2011 3:24:57 PM PDT by VanDeKoik (1 million in stimulus dollars paid for this tagline!)
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To: cripplecreek
This Amy Mainzer?


5 posted on 11/02/2011 3:29:38 PM PDT by Paladin2
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To: SunkenCiv

So let me get this straight.... If you dropped Obama and Biden’s brain at the same time....

Oh never mind.


6 posted on 11/02/2011 3:29:38 PM PDT by Bullish (Recovery won't begin until Obama loses HIS job.)
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To: VanDeKoik

7 posted on 11/02/2011 3:32:24 PM PDT by gargoyle (...it becomes necessary for one people to dissolve the political bands which have connected them...)
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To: Bullish
So let me get this straight.... If you dropped Obama and Biden’s brain at the same time....

Yes, you got it, they'd both float

8 posted on 11/02/2011 3:35:34 PM PDT by stormhill
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To: Bullish

That would be like dropping Santa Claus and the Tooth Fairy at the same time.


9 posted on 11/02/2011 3:38:17 PM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: cripplecreek

It’s a good idea, because the only way I could get anything out of that show would be to listen and not watch. ;’)


10 posted on 11/02/2011 3:56:23 PM PDT by SunkenCiv (It's never a bad time to FReep this link -- https://secure.freerepublic.com/donate/)
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To: VanDeKoik

;’)


11 posted on 11/02/2011 3:56:41 PM PDT by SunkenCiv (It's never a bad time to FReep this link -- https://secure.freerepublic.com/donate/)
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To: Paladin2

When she was written out, the show passed its peak. Still like it though.


12 posted on 11/02/2011 3:57:40 PM PDT by SunkenCiv (It's never a bad time to FReep this link -- https://secure.freerepublic.com/donate/)
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To: Bullish; stormhill; DuncanWaring
Image and video hosting by TinyPic

13 posted on 11/02/2011 4:00:54 PM PDT by SunkenCiv (It's never a bad time to FReep this link -- https://secure.freerepublic.com/donate/)
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To: SunkenCiv

The hammer will fall slightly faster, as every mass has it’s own gravity. The hammers greater mass has greater gravitational pull on moon.


14 posted on 11/02/2011 4:06:10 PM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: Bullish
>"If you dropped Obama and Biden’s brain at the same time..."

You'd be stoned stupider than Ozzy.

15 posted on 11/02/2011 4:07:42 PM PDT by rawcatslyentist (It is necessary that a person be born of a father who is a citizen; ~Vattel's Law of Nations)
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To: SampleMan
The hammer will fall slightly faster, as every mass has it’s own gravity.

I hadn't thought of it that way but it does make some sense. You would need a very long fall to show the difference to the naked eye.
16 posted on 11/02/2011 4:10:31 PM PDT by cripplecreek (A vote for Amnesty is a vote for a permanent Democrat majority. ..Choose well.)
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17 posted on 11/02/2011 4:44:47 PM PDT by RedMDer (Forward With Confidence!)
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To: SampleMan
The hammers greater mass has greater gravitational pull on moon.

That's true, but the "greater gravitational pull" is balanced by that fact that there's a greater mass to be accelerated.

18 posted on 11/02/2011 4:46:33 PM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: Bullish

“Brain’’? Obama and Biden!?! What makes you think either of those two have a brain?


19 posted on 11/02/2011 4:50:49 PM PDT by jmacusa (Political correctness is cultural Marxism. I'm not a Marxist.)
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To: DuncanWaring

Also true.

You could move a supermassive black hole with a feather if you could anchor the feather somehow and had a few billion years to do it in.


20 posted on 11/02/2011 4:56:02 PM PDT by cripplecreek (A vote for Amnesty is a vote for a permanent Democrat majority. ..Choose well.)
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To: SampleMan

Forgive my advanced ignorance, but doesn’t the mass have to rotate to induce the gravity field? Or have I drowned in a sea of sci-fi hog swill.

Regards


21 posted on 11/02/2011 5:02:38 PM PDT by moose07
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To: cripplecreek

A variation on that concept has been suggested as a means of altering the trajectories of asteroids that appear to be on earth-colliding trajectories.


22 posted on 11/02/2011 5:04:34 PM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: moose07

Negative on the rotation.

That’s why it’s called science “fiction”.


23 posted on 11/02/2011 5:07:30 PM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: DuncanWaring

Thank you.
The clue was in the name I suppose!

Regards.


24 posted on 11/02/2011 5:16:18 PM PDT by moose07
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To: moose07
Rotation has no effect on gravitational pull, just the ability to resist it via centripetal force.
25 posted on 11/02/2011 5:46:07 PM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: DuncanWaring
That's true, but the "greater gravitational pull" is balanced by that fact that there's a greater mass to be accelerated.

Negative. All mass has the same reaction to gravitational forces, inertia and force are linear. 1000 lb takes more to get moving than 100 lb, but there IS more to get it moving.

26 posted on 11/02/2011 5:49:52 PM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: cripplecreek
I hadn't thought of it that way but it does make some sense. You would need a very long fall to show the difference to the naked eye.

At the hammer and feather scale it is so minute to be almost ridiculous, but think of it this way. If you could stop the Earth and Moon from rotating and place a feather the same distance from Earth as the Moon, I guarantee that we will collide with the Moon first.

27 posted on 11/02/2011 5:53:09 PM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: SampleMan

Gravity is probably the best know yet least understood force in nature.

We think of people on the space station as being weightless but that’s really just an effect of the free fall they’re in. I think I read that the gravitational pull at that distance from the earth’s surface is less than 1% less than it is at sea level.


28 posted on 11/02/2011 6:04:16 PM PDT by cripplecreek (A vote for Amnesty is a vote for a permanent Democrat majority. ..Choose well.)
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To: SampleMan

To avoid any complications due to different compositions, instead of a feather use a small iron ball of the same mass, and the USS Missouri, also generally made of iron.

Suspend them each one mile above the surface of the moon.

Each is composed of a collection of iron atoms.

The gravitational attraction between each atom of iron and the moon is the same, thus each atom of iron (assuming all of the same isotope) will accelerate towards the moon at the same rate.

Therefore, since the featherweight piece of iron and the Missouri are both merely composed of many atoms of iron, though in different numbers, accelerating at the same rate, “in formation”, they will both hit the moon at the same time.

This holds for any distance from the moon.


29 posted on 11/02/2011 7:26:24 PM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: cripplecreek

The gravitational attraction between two objects is proportional to the product of the masses of the two objects divided by the square of the distance between the two objects.

Assume, to avoid having to do triple integrals, all mass of the earth is concentrated at a very dense point at the center of the earth, surrounded by a massless, 4000-mile-radius shell that we stand on.

We are thus separated from the mass of the earth by 4000 miles, which, squared, has a magnitude of 16000000.

The orbit of the ISS has an average altitude of about 225 miles.

It, then, is about 4225 miles from the mass of the earth; 4225 squared is about 17850000.

Therefore, the gravitational pull of the earth at the altitude of the space station is 16000000/17850000 relative to that on earth, or roughly 90%.

Even if you assume the far half of the earth doesn’t exist because the “1 over r-squared” term makes it less important and use a radius of 2000 miles rather than 4000, that still puts the earth’s gravitational attraction on the ISS equal to about 80% of that on the surface of the earth.


30 posted on 11/02/2011 7:39:27 PM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: DuncanWaring

LOL I’ll take your word for it. I love the science but really suck at the math.


31 posted on 11/02/2011 7:51:41 PM PDT by cripplecreek (A vote for Amnesty is a vote for a permanent Democrat majority. ..Choose well.)
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To: cripplecreek; SampleMan
Thank you for demonstrating the failure of "hand-waving Physics".

Let's try math, instead of handwaving. We wish to determine the acceleration due to gravity acting upon an object as a function of its proximity to some other object. The two objects are (let us say) a hammer, and the moon. The each have mass Mh and Mm. According to Newton, a force acting on a mass M causes acceleration.

F=m*a

The gravitational force between two massive objects can be computed

Fg = G*(M1*M2)/ R2

where "R" is the distance between them. So, the gravitational acceleration of a hammer falling on the moon may be calculated:

Fg = G*(Mm*Mh)/ R2 = Mh*a

Note that Mh cancels out of this equation. Acceleration of an object (a hammer) due to the gravitational attraction of another object (the moon) is not a function of the first object's (the hammer) mass.

32 posted on 11/02/2011 7:56:31 PM PDT by ArrogantBustard (Western Civilization is Aborting, Buggering, and Contracepting itself out of existence.)
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To: ArrogantBustard

I’m impressed.

I knew what the equations were, but lacked the ambition to actually “typeset” them in HTML.


33 posted on 11/02/2011 8:04:27 PM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: DuncanWaring

“Typesetting” them is the only way I know of to make them readable. My knowledge of HTML is really quite limited.


34 posted on 11/02/2011 8:15:28 PM PDT by ArrogantBustard (Western Civilization is Aborting, Buggering, and Contracepting itself out of existence.)
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To: ArrogantBustard

I guess < sub > and < super > handles most of it.

That, and ambition.


35 posted on 11/02/2011 8:19:00 PM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: ArrogantBustard
Acceleration of an object (a hammer) due to the gravitational attraction of another object (the moon) is not a function of the first object's (the hammer) mass.

Really, so Jupiter and Earth have the same pull on the sun in your world.

You only did half of the equation.

36 posted on 11/03/2011 5:03:13 AM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: DuncanWaring

If gravity is as you say, why do object accelerate faster in a fall on Earth than they do on the moon.

As in your example, the Earth and the Moon are just groupings of individual atoms right?

Again, you are only doing half of the equation.


37 posted on 11/03/2011 5:16:17 AM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: cripplecreek

Indeed, it is impossible to find zero gravity anywhere matter exists, but it is possible to find points and conditions of balanced gravity, which have the same obervable result.


38 posted on 11/03/2011 5:18:29 AM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: SampleMan

Lately I’ve been wondering about the concept of true motionlessness. I wonder if its even possible in expanding space where all things are moving at incredible speeds.


39 posted on 11/03/2011 5:24:48 AM PDT by cripplecreek (A vote for Amnesty is a vote for a permanent Democrat majority. ..Choose well.)
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To: SampleMan
I did NOT do "half the equation".

Objects accelerate faster in a fall on Earth than they do on the Moon because Earth is bigger than the Moon. Work the equations for yourself. Substitute the mass of Earth, Jupiter, another hammer, whatever you like. You can solve for the acceleration towards any of these.

Gravitational acceleration towards any object X is a function of the mass of that object and the distance from that object, as I showed upthread.

Don't wave your hands, do the math.

40 posted on 11/03/2011 5:41:51 AM PDT by ArrogantBustard (Western Civilization is Aborting, Buggering, and Contracepting itself out of existence.)
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To: ArrogantBustard
Dear arrogant.

Do two magnets with their N S poles facing each other create a greater attractive force than a single magnet? If the force is greater doesn't that equate to greater acceleration?

If a hammer were orbiting the Earth, it would not measurably effect the tides, but the moon does. Hmmm. Why is that? Because the large object exerts greater force. Hmmm. Going back into your acceleration formulas.

As I said, you forgot that the equation has to be made for both objects, not just one, and then the result combined.

Math is great, but garbage = garbage out. Acceleration of gravity formulas must use the mass of both objects. With small objects we don't do this because it doesn't matter (measurably), but with large objects we absolutely combine the masses.

The attraction between the Earth and Moon is determined using the combined mass of both, not the mass of the Earth. This is easily understood if you think of what would happen if you pushed the Earth and Moon into one ball. That ball would have a greater gravitational attraction than the Earth right? Sure, so the same applies before they are combined.

41 posted on 11/03/2011 6:07:10 AM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: cripplecreek

All measurements of movement are relative to an arbitrarily chosen position.


42 posted on 11/03/2011 6:08:22 AM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: ArrogantBustard
Note that Mh cancels out of this equation. Acceleration of an object (a hammer) due to the gravitational attraction of another object (the moon) is not a function of the first object's (the hammer) mass.

What you are clearly doing is treating one of the masses as a parent mass, and ignoring the other.

According to your equation, if we swapped the moon and hammer as M1 and M2, the gravitational force would immediately drop off to near nothing.

Indeed, do the math.

43 posted on 11/03/2011 6:16:56 AM PDT by SampleMan (Feral Humans are the refuse of socialism.)
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To: SampleMan
Objects accelerate faster in a fall on Earth than they do on the Moon, because each atom of the "falling" object is attracted to each and every atom of the Earth (or the Moon), and the Earth has a lot more atoms.

It's like taking two identical rubber bands and stretching one to twice its unstretched length. That will produce a certain amount of tension. If you then stretch both that same amount, you'll get twice the force.

Same thing for inter-atomic attractions.

44 posted on 11/03/2011 7:28:05 AM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: cripplecreek

Hey, why is it always just pretty girls? Of course, at my age, I’d just as soon have pictures of pretty dogs. :)


45 posted on 11/03/2011 7:34:36 AM PDT by brytlea (An ounce of chocolate is worth a pound of cure)
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To: Bullish

Another big lie! Biden doesn’t have a brain....


46 posted on 11/03/2011 7:35:19 AM PDT by brytlea (An ounce of chocolate is worth a pound of cure)
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To: ArrogantBustard

Oh my goodness. I think I’m better at handwaving! :)


47 posted on 11/03/2011 7:38:36 AM PDT by brytlea (An ounce of chocolate is worth a pound of cure)
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To: SampleMan; ArrogantBustard
As I said, you forgot that the equation has to be made for both objects, not just one, and then the result combined.

If you go back and read what AB posted, he said exactly that:

The gravitational force between two massive objects can be computed

Fg = G*(M1*M2)/ R2

That's the force BETWEEN any two objects - that same force acts equally on each of the two objects.
48 posted on 11/03/2011 7:41:31 AM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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To: brytlea
Hey, why is it always just pretty girls?

You really want pictures of Stephen Hawking?
49 posted on 11/03/2011 7:45:24 AM PDT by cripplecreek (A vote for Amnesty is a vote for a permanent Democrat majority. ..Choose well.)
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To: SampleMan
...if we swapped the moon and hammer as M1 and M2, the gravitational force would immediately drop off to near nothing.

The gravitational force would be unchanged.

Have you never heard of the "Commutative property of multiplication"?

Apparently not.

Let me introduce you to it: "Two numbers can be multiplied in either order."

This means that a room that is 10' x 15' has the same floor area as a room that is 15' x 10'.

50 posted on 11/03/2011 7:49:07 AM PDT by DuncanWaring (The Lord uses the good ones; the bad ones use the Lord.)
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