what are you reading now?

[IdleRich]

Weight is just mass,

No not really weight is a force measured in newtons, mass is how much of something there is.

with local gravity as a sort of coefficient, right?

But yeah mass x acceleration due to gravity does give you the weight.

When you hit a nail with a hammer the hammer will stop moving. The change in momentum is called the impulse. The impulse is given by time of contact x force and the momentum is mass x velocity.

So the force applied is change of momentum/time

The ending momentum is zero so the change in momentum is really just the starting momentum which is the mass of the hammer x speed it's moving.

Force applied = (mass of hammer x speed)/(time of contact with nail)

Which doesn't depend on the gravity.

 

[IdleRich]

See here for eg

https://www.thoughtco.com/mass-and-weight-differences-606116

 

[Clinamenic]

Thanks that clears things up for me. I wasn't connecting the dots between weight being understood in terms of newtons, and gravity itself being understood as an acceleration.

 

[Clinamenic]

Like I didn't realize that saying W = m x g (ie what I was saying) was getting at the same thing as was a sort of rephrasing of saying F = kg x m / s^2, but that article you just shared cleared things up further.

 

[IdleRich]

Thanks that clears things up for me. I wasn't connecting the dots between weight being understood in terms of newtons, and gravity itself being understood as an acceleration.

Well the constant referred to as g is acceleration due to gravity, not gravity itself. The force on a body due to gravity is its weight.

 

[Clinamenic]

I see, a conflation I wasn't aware I was making.

 

[Clinamenic]

This stuff is fascinating, to think that these formulae grant us some understanding of how massive bodies nucleate and heavier elements form.

 

[Mr. Tea]

This is what I mean though, he thinks a blow from a hammer would have no force cos he's mixed up mass and weight. He seems to think that its mass would have decreased so it was like an inflatable hammer.

He hasn't said it would have no force, he just said it's impossible. It could be that he's implying it literally has no momentum, or very little, because of the reduced gravity, which would be very silly. I'm being a bit more generous and assuming it's a problem of coordination, because the brain is fooled by the hammer's reduced (compared to earth) weight, coupled with its unchanged inertial mass.

You could be right, though. The thing about the frost on the moon vehicle makes me think this isn't a very thoroughly scientific bit of sci-fi (although it's clearly trying to be).

The film Moon I found a bit frustrating, for the same reason.

 

[Clinamenic]

@Mr. Tea what do you think of Interstellar? It had Kip Thorne of Caltech as a consultant, I believe.

 

[IdleRich]

Like I didn't realize that saying W = m x g (ie what I was saying) was getting at the same thing as was a sort of rephrasing of saying F = kg x m / s^2, but that article you just shared cleared things up further.

You can do a kind of dimensional analysis to understand this better maybe.

 

[IdleRich]

He hasn't said it would have no force, he just said it's impossible. It could be that he's implying it literally has no momentum, or very little, because of the reduced gravity, which would be very silly.

I'm pretty sure that is precisely the mistake he's making

 

[IdleRich]

He doesn't say it's difficult, he says it is impossible - he thinks the hammer is so light it can't possibly move the nail

 

[Clinamenic]

He doesn't say it's difficult, he says it is impossible - he thinks the hammer is so light it can't possibly move the nail

Hmm, interesting. Could be that a tool which feels light to us on earth doesn't have sufficient mass, in more absolute terms, to drive a nail into a given surface. And so the faulty logic could be the conclusion that a tool with sufficient mass in absolute terms, but in the context of the moon, can't drive the same nail into the same surface because the tool feels lighter there than it does here.

 

[Mr. Tea]

@Mr. Tea what do you think of Interstellar? It had Kip Thorne of Caltech as a consultant, I believe.

Not seen it. But Thorne is a theorist, so I wouldn't be surprised if the show got every subtle detail about gravitational lensing or relativistic time dilation absolutely spot on, but also somehow forgot that humans can't breathe in a vacuum, or that the time needed to boil an egg is measured in minutes rather than nanoseconds or years.

 

[Clinamenic]

i.e. the confusion could be between the sensation of wielding a hammer, and the ostensibly constant characteristics of the hammer such as its mass.

 

[Mr. Tea]

He doesn't say it's difficult, he says it is impossible - he thinks the hammer is so light it can't possibly move the nail

Actually that does seem like a fair reading of "impossible", so I guess you're right.

 

[Clinamenic]

Not seen it. But Thorne is a theorist, so I wouldn't be surprised if the show got every subtle detail about gravitational lensing or relativistic time dilation absolutely spot on, but also somehow forgot that humans can't breathe in a vacuum, or that the time needed to boil an egg is measured in minutes rather than nanoseconds or years.

I really enjoy Interstellar, and Thorne apparently worked closely with the GCI team to render the black hole and other such things.

 

[Mr. Tea]

I really enjoy Interstellar, and Thorne apparently worked closely with the GCI team to render the black hole and other such things.

Should've asked the guys who wrote Spinal Tap about the effects they should use to get the right shade of black.

 

[Clinamenic]

Vantablack

 

[mixed_biscuits]

Vantablack