[stevegraham (OP)]

An astronaut has a mass of 55kg on Earth. Would the astronauts weight be different on the ISS?

[Halc]

An astronaut has a mass of 55kg on Earth. Would the astronauts weight be different on the ISS?

First of all, 55kg is a mass, not a weight. I presume he weighs about 539 newtons here on Earth.
Yes, it would be zero newtons on the ISS, which is 'different'. That's what it means to be weightless in space.
He would on the other hand continue to mass 55kg, which could be measured by a mass scale instead of a weight scale.  Most of the mass scales on Earth require at least some gravity. I have one that would measure no difference if I stood on it on the surface of the moon.

So it is interesting to design one for zero-G environments.

[Origin]

An astronaut has a mass of 55kg on Earth. Would the astronauts weight be different on the ISS?

Using Newtonian physics the acceleration due to gravity on the earths surface is:

Where
is the gravitational constant,
is the mass of earth,

is the radius of the earth, 6400 km or 6,400,000 m



So on earth an astronaut with a mass of 55 kg would weigh,

55 kg x 9.81 m/s^2 =   540 N
Or
540 N x 0.2248 lb/Ǹ = 121 lbs.

The ISS is about 400 km in altitude.  So it's distance from the center of the earth is 6800 km or 6,800,000 m.
So the acceleration due to gravity at that distance is:



So at an altitude of 400 km above the surface of the earth a mass of 55 kg would weigh,

55 kg x 8.7 m/s^2 =   480 N
Or
480 N x 0.2248 lb/Ǹ = 108 lbs.

However as we know the astronauts experience weightlessness while on the ISS.  The reason the astronauts are weightless is because they are in freefall due to being in orbit.  In other words the ISS is continuously falling towards earth, however due to its high velocity moving at 90 degrees to the direction of the pull of gravity it continually misses the earth.

[alancalverd]

Wikipedia:

Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar quantity, the magnitude of the gravitational force. Yet others define it as the magnitude of the reaction force exerted on a body by mechanisms that counteract the effects of gravity: the weight is the quantity that is measured by, for example, a spring scale.

So the answer is that she (55 kg would be a rather small  male) weighs 480 newtons or zero, depending on whether you calculate it or measure it!

[Halc]

So the answer is that she (55 kg would be a rather small  male) weighs 480 newtons or zero, depending on whether you calculate it or measure it!

If your calculation yields a different number than the one measured, then the calculation is wrong.
480 newtons (as calculated above) is ones weight at the top of a ~400 km tower erected at the pole.  The calculation for the ISS is far more trivial.

[evan_au]

it is interesting to design (a scale) for zero-G environments.

See: https://www.popularmechanics.com/space/a14427198/the-complex-contraption-astronauts-use-to-weigh-themselves-in-space/

[Petrochemicals]

480 N x 0.2248 lb/Ǹ = 108 lbs.

Mass is mass irregardless. I accept Newton's.

[Bored chemist]

irregardless.

That's not a real word.

[alancalverd]

It's in remarkably common use, along with other pointless neologisms such as "in regards to".

Oddly, if you deconstruct the word it sort of means the same (and indeed the opposite of what was intended) though why nobody under the age of 50 can say "regarding" baffles me.

[Bored chemist]

Oddly, if you deconstruct the word it sort of means the same, though why nobody under the age of 50 can say "regarding" baffles me.

You seem to have misspelled "about".

[Janus]

It's in remarkably common use, along with other pointless neologisms such as "in regards to".

Oddly, if you deconstruct the word it sort of means the same (and indeed the opposite of what was intended) though why nobody under the age of 50 can say "regarding" baffles me.

It's like when someone says, "I could care less", when they mean "I couldn't care less".  If you could care less, then you obviously care at least some now.

[jeffreyH]

irregardless.

That's not a real word.

Don't misunderestimate the power of linguists.

[jeffreyH]

An astronaut has a mass of 55kg on Earth. Would the astronauts weight be different on the ISS?

In one sentence you use mass and in the other you use weight. Make your mind up. Which is it?

[Bored chemist]

An astronaut has a mass of 55kg on Earth. Would the astronauts weight be different on the ISS?

In one sentence you use mass and in the other you use weight. Make your mind up. Which is it?

I don't think the OP understands why this is a problem.
It's like saying "His mass on Earth is 55Kg; is his birthday different on the ISS?".

[Petrochemicals]

https://en.m.wikipedia.org/wiki/Irregardless

Extra ordinary, extrodinary

[jeffreyH]

https://en.m.wikipedia.org/wiki/Irregardless

Extra ordinary, extrodinary

I did warn ya BC!

[alancalverd]

t's like when someone says, "I could care less", when they mean "I couldn't care less".  If you could care less, then you obviously care at least some now.

Seems to be an Americanism. It makes sense if it's an abbreviation of "well I could care less, but with some difficulty".

Much confusion has arisen in board meetings when my American colleagues say "let's table that", meaning "put it aside" and the Brits assume they mean "tackle it immediately".   

Also worry about the elliptical "protest". Protesting your religion means being enthusiastic about it, but across the pond, protesting the police means complaining about them.

And the dangers of walking on the pavement....

Meanwhile, back in Blighty, surely an ex-pat is someone who has renounced Irish nationality, whereas an expat is someone who has retained his nationality but lives abroad.

And why do people say "diffuse" (spread around) when they mean de-fuse (pretty much the opposite).

Now what were we talking about?

[alancalverd]

Quote from: alancalverd on 05/05/2021 19:51:59
So the answer is that she (55 kg would be a rather small  male) weighs 480 newtons or zero, depending on whether you calculate it or measure it!
If your calculation yields a different number than the one measured, then the calculation is wrong.

No, the true weight is indeed 480 N, which is why she is in orbit: gravity is providing the centripetal force.

The problem is that you can't measure it with a conventional balance in the same orbit.

[CliffordK]

Keep in mind that one isn't without the effects of gravity on the ISS.

One is in a state of constant freefall counteracted perfectly by the orbital velocity of the ISS (and everything inside).

So, on Earth, the acceleration due to gravity is about 9.8

At an altitude of about 420 km, the acceleration due to Earth's gravity on the ISS is about 8.63

https://www.vcalc.com/wiki/KurtHeckman/Gravity+Acceleration+by+Altitude