http://twitter.com/Astro_Mike [twitter.com]

one of the astronauts is live blogging on twitter from the shuttle

Um, it's the pound [wikipedia.org]. Doesn't everyone know that? 2.2 lbs to the kilo.

While weight certainly means the force created between two masses due to gravity, it is almost always used interchangeably with mass in practice.

-Peter

Sorry to reply to my own post but... I just realized that Duracell already did a space commercial [youtube.com] about an IMAX camera being used in space.

Pound-mass or slug, your choice.

Still messed up. Trying to compare a metric unit of mass to a imperial unit of weight using a conversion factor that only works at roughly sea level on earth.

Metric unit of weight - Newton N
Metric unit of mass - Gram g

Imperial unit of weight - Pound lb (you know, like Pound Sterling being a pound of silver?)
Imperial unit of mass - Slugs

Did you click the link? No one uses slugs. Pounds are commonly used to express mass as well as force (weight).

Since there is a mass version of the pound, and it is defined in terms of kilos the conversions actually work perfectly in any (or no) gravitational field. (Though the conversion factor is exactly 2.20462262, not 2.2.)

Seriously, click the link.

Don't get me wrong in all of this. I advocate the metric system. But I don't understand the seemingly willful misunderstanding of the modern imperial system.

-Peter

Technically the batteries have the same mass while on Earth as they do while orbiting it. The weight in orbit is zero. (which is the point the above are making)

See here: http://en.wikipedia.org/wiki/Mass_versus_weight [wikipedia.org]

Are you "weightless" while skydiving?

Only briefly. Once you hit terminal velocity, there is no longer any sensation of falling (no acceleration). For the vast majority of your dive, you "weigh" the same as you do on the ground. Instead of being held up by the floor or a piece of furniture, you are held up by a (relative to you) fast-moving updraft.

Technically the batteries have the same mass while on Earth as they do while orbiting it. The weight in orbit is zero.

Okay, but you're talking about the lack of the sensation of weight [wikipedia.org].

If there is no contact with any surface to provide such an opposing force then there is no sensation of weight (no apparent weight). This happens in free-fall, as experienced by sky-divers (until they approach terminal velocity) and astronauts in orbit, who feel "weightlessness" even though their bodies are still subject to the force of gravity: they're just no longer resisting it. The experience of having no apparent weight is also known as microgravity.

I wasn't confusing mass with weight, but you still need to exert force to support an object in a gravitational field, and the measure of that force is its weight. The fact that we're in free fall and the object is weightless relative to us doesn't change that.

(IANAAP, so correct me if I'm wrong).

mms://209.73.189.79/bcpenc252181?StreamID=81684353&pl_auth=56e0ca2df8a3b81fa447c77c49dbf0f1&ht=120&pl_b=00CEBE2C2D18A488577820B4444A1179CB&CG_ID=1369080&Segment=149773

There's no question that it's a kludge.

The "mass pound" and "weight pound" may be equal at sea level in a certain location or whatever, but probably not equal at any other gravitational potential

There's no "may" about it. For the Math to work they can only be equal at exactly 1G. The thing is, we never really use the "weight pound" in practice. I mean, if someone asks you what you weigh do you ask for a reference altitude (or gravitational force)? Absurd.

Put it this weigh (yuk-yuk), if you want to buy a pound of bananas, are you looking for half a kilo of bananas? Or four and a half newtons of bananas?

Always glad to rise above the hoi polloi ;-)

-Peter