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Bob
2003-Jun-22, 08:10 PM
"Car Talk" is a terrific radio show on NPR and this week's puzzler has an astronomical bent. Let's stipulate that the force of gravity at the Moon's surface is one sixth that of Earth. So an object weighing 300 pounds on a bathroom-type scale on Earth would weigh 50 pounds with the same setup on the Moon. Question: can you think of anything that would weigh MORE on the Moon.
I think I have the answer. The hosts will divulge their answer on next week's show.

dgruss23
2003-Jun-22, 08:13 PM
Would the scale itself be capable of "weighing" more?

Chuck
2003-Jun-22, 08:16 PM
A balloon partially filled with helium could be made to weigh nothing on earth and would weigh more on the moon.

Grand Vizier
2003-Jun-22, 08:20 PM
"Car Talk" is a terrific radio show on NPR and this week's puzzler has an astronomical bent. Let's stipulate that the force of gravity at the Moon's surface is one sixth that of Earth. So an object weighing 300 pounds on a bathroom-type scale on Earth would weigh 50 pounds with the same setup on the Moon. Question: can you think of anything that would weigh MORE on the Moon.
I think I have the answer. The hosts will divulge their answer on next week's show.

Please promise you'll post the answer here. I know that this one will be going round and round in my head for ever otherwise - or unless I can think of an answer.

Grand Vizier
2003-Jun-22, 08:24 PM
A balloon partially filled with helium could be made to weigh nothing on earth and would weigh more on the moon.

Doh. Yes, of course. So a rig with helium- or hydrogen-filled balloons attached, filled with helium - or hydrogen - could be made to weigh any arbitrarily tiny amount here, but would display its full mass/6 on the Moon. I would have got that, eventually, honest. :wink:

pixelator
2003-Jun-22, 11:41 PM
Actually, the answer could be even simpler: Air

Air weighs nothing (on a scale) here on earth. But on the moon a bag of air would register weight on the scale.

Donnie B.
2003-Jun-23, 01:04 AM
Well, a bag of air would weigh something on Earth. No fair omitting the bag here if you're going to use it on the Moon! I guess you'd need to make the bag big and light enough so that the 6x weight of the bag (here) would be cancelled out by the 1/6 weight of the air (there).

Avatar28
2003-Jun-30, 08:23 PM
Okay, those who said helium baloons give yourselves a pat on the back. That was, indeed, the answer.

tracer
2003-Jul-01, 02:19 AM
Of course, this answer assumes that "on the moon" means "out of doors on the moon surrounded by vacuum."

Inside a pressurized Apollo Lunar Module or a hypothetical dome-enclosed lunar colony, air and helium would have the same buoyancy on the moon as they do in the same air pressure here on Earth.

However, out in the normal vacuum on the surface of the moon, we can take solace in the fact that, although the Hindenburg would weigh more, it wouldn't catch on fire.

ToSeek
2003-Jul-01, 03:38 AM
Of course, this answer assumes that "on the moon" means "out of doors on the moon surrounded by vacuum."

Inside a pressurized Apollo Lunar Module or a hypothetical dome-enclosed lunar colony, air and helium would have the same buoyancy on the moon as they do in the same air pressure here on Earth.

For the lunar module, at least, that's not true: the atmosphere was pure oxygen at 5 psi, so a helium balloon would have been less buoyant than in a standard atmosphere.

GurneyHalleck
2003-Jul-01, 04:12 PM
Maybe I'm just being a stickler here, but I say the weight of the helium balloon on Earth is still higher than what it would be on the moon. The weight of the balloon should just be it's mass times gravity. The fact that it's pushed up on Earth because it's lighter than air shouldn't be taken into account - that's an outside force. Since the balloon has the same number of balloon atoms (yes, balloon is an element) and helium atoms on the Earth and the moon, it's mass is the same in either place. Therefore, it's weight is lighter on the moon since gravity is lower there.

tracer
2003-Jul-01, 04:33 PM
Since the balloon has the same number of balloon atoms (yes, balloon is an element)
Why, you're right! It's right there on the periodic table: Ba, element 56, sandwiched right between cesium and the lanthanides!

Donnie B.
2003-Jul-01, 05:06 PM
I wonder what sort of super-rubber they use to make helium balloons that don't pop when you take them outdoors on the Moon!

On the "weight of the Hindenberg" question, I guess it all depends on your definition of weight. If you mean the mass, then it doesn't change wherever you go (barring relativistic effects). But "weight" generally means "the reading you get when you place the object on a scale", which would be zero (actually negative) for a lighter-than-air craft.

This is an ironic case, actually, since a lot of people use "weight" when they really mean "mass", but this time it's the other way around!

somerandomguy
2003-Jul-01, 06:51 PM
My question is, couldn't the answer then be "a helicopter with its motor running"?

kilopi
2003-Jul-01, 07:16 PM
This is an ironic case, actually, since a lot of people use "weight" when they really mean "mass", but this time it's the other way around!
Wouldn't the other way around be if someone used "mass" when they really meant "weight"?

My question is, couldn't the answer then be "a helicopter with its motor running"?
Sure, but they don't usually weigh helicopters that way.

calliarcale
2003-Jul-01, 08:56 PM
I wonder what sort of super-rubber they use to make helium balloons that don't pop when you take them outdoors on the Moon!

Actually, it shouldn't be too difficult. The balloon just has to be able to withstand at least 14 PSI. And if you don't think latex balloons are very strong, just try filling them with something much heavier than air -- like water. Water balloons break easily, but they'll hold a surprising amount of water if you handle them gently.

Contrary to popular thought (and contrary to what I saw Gene Cernan say on a really cool TV program about four-wheel drive vehicles which called the LRV the most sophisticated 4WD ever built), tires would not explode on the moon, and neither would a lot of inflatable things popularily used on Earth. The real reason wire mesh was used on the LRV wheels was weight, not strength. Rubber is heavy. ;) The Space Shuttle uses fairly normal tires, manufactured by Michelin for aeronautical applications. The wheel wells are not pressurized, however, so these tires are exposed to vacuum while inflated. They don't explode because if a tire can tolerate being inflated to 300 PSI (the normal inflation of a Space Shuttle tire), a measley 14 PSI difference isn't going to amount to a whole lot.

gethen
2003-Jul-01, 09:24 PM
Since the balloon has the same number of balloon atoms (yes, balloon is an element)
Why, you're right! It's right there on the periodic table: Ba, element 56, sandwiched right between cesium and the lanthanides!

This is clearly an attempt to get back in Ba's good graces.

Avatar28
2003-Jul-01, 09:47 PM
Maybe I'm just being a stickler here, but I say the weight of the helium balloon on Earth is still higher than what it would be on the moon. The weight of the balloon should just be it's mass times gravity. The fact that it's pushed up on Earth because it's lighter than air shouldn't be taken into account - that's an outside force. Since the balloon has the same number of balloon atoms (yes, balloon is an element) and helium atoms on the Earth and the moon, it's mass is the same in either place. Therefore, it's weight is lighter on the moon since gravity is lower there.

No, you have to look at the wording of the question.

RAY: All of us remember from our high school or junior high school physics, that the Moon has a fraction of the Earth's gravity. In fact, we were all told that it's a sixth the gravity of the Earth.

When those NASA guys faked the landing on the Moon, they were very careful to show the astronauts bounding from one spot to another, like they were kangaroos.

TOM: How DID they fake it?

RAY: Springs. Invisible wires. You've never seen Peter Pan? Anyway… for example, if you had a bathroom scale, and you put your 600-pound...

TOM: mother-in-law?

RAY: I knew you were going say that! If you put your 600-pound Bengal tiger on this bathroom scale, and then transport the tiger and the bathroom scale to the Moon, the Bengal tiger (or the mother-in-law), would weigh 100 pounds.

You with me?

TOM: I'm with you.

RAY: Here's the question. Is there anything you can think of that, if measured in the same way, would weigh more on the Moon than it does on the Earth? Now, I have an answer in mind, but there may be more than one right answer.

GurneyHalleck
2003-Jul-02, 04:44 PM
Yes, I see...

But the question at the start of this thread was simply: can you think of anything that would weigh MORE on the Moon. With the implied "using a scale", you are of course correct!

kilopi
2003-Jul-02, 05:45 PM
Now that you bring that up, I can think of a lot of things that would be just as dense on the moon...

David Hall
2003-Jul-04, 04:14 PM
Now that you bring that up, I can think of a lot of things that would be just as dense on the moon...

A Moon Hoax believer, for one?

kilopi
2003-Jul-04, 04:18 PM
Yes! good answer. But if we performed the experiment correctly, we could probably kill two birds with one stone.

Ducky
2003-Jul-04, 04:51 PM
Sigh.

Okay, I just read the question and the answer to my husband (disinfo agent mentioned in the PX forum), and he's arguing quite profusely that anything on the moon would weigh the same amount it does on Earth.

Please give me a layman's-terms explanation so that I can set him straight. Or, an explanation proving me wrong. Either way.

Quack.

Said hubby is now laughing at me :lol:

kilopi
2003-Jul-04, 05:29 PM
Just show him the Car Talk stuff. If he doesn't believe them, they'll just laugh at him. :)

Kaptain K
2003-Jul-04, 06:03 PM
Ducky,
Your husband is confusing mass with weight. An object with a mass of 100 Kg will have a weight of 10.2 Newtons on Earth. On the Moon, its mass will still be 100 Kg, but its weight will be 1.7 N.

Irishman
2003-Jul-05, 06:37 AM
The conventional explanation is that mass is a measure of the amount of material, while weight is a measure of the pull of gravity (a force). Weight can be measured by a spring scale, whereas mass is measured with a balance.

The confusion is perpetuated by the use of the American system of units, and the pound (lb). Pounds are technically a measure of weight, the force caused by the pull of gravity on the object. However, because of the history of the origin of the unit and tradition, things are often measured in weight that should strictly speaking be measured in mass - airplane weight, weight of cargo for shipment, etc. This is because of the use of standard gravity acceleration at the Earth's surface.

Another confounding factor is when engineers sometimes use a unit of convenience called the pound-mass (lbm), differentiated from the pound-force (lbf). This is purely conceptual and is, strictly speaking, incorrect. In order to use pounds as a measure of mass (lbm), they require a conversion factor called gc (g sub c). G sub c is conveniently 32.2 ft-lbm/lbf-sec2 - the same numerical amount as the standard acceleration of gravity, with units for proper conversion. In other words, the mass is converted by a standard factor to weight units and still pretended to be mass units. This is one of the reasons SI is so much better.

Don't get me started about the time a college textbook presented a problem with units of kilogram-force.

kilopi
2003-Jul-05, 11:28 AM
The confusion is perpetuated by the use of the American system of units, and the pound (lb).
And then there's also that kilograms, a unit of mass, are also used as a unit of weight, often enough.

Don't get me started about the time a college textbook presented a problem with units of kilogram-force.
Oops.