Do Floating Objects Have 'Weight'?

[inventor]

Sorry, the bathroom scales used on Earth, use the same spring mechanism, or algorithms for electronic scales. They won't recalculate the Metric equations, because they know they are on the Moon. And a balance scale has the same result regardless of the strength of the field of gravity the device is experiencing.

That means, metric scales, will show the same difference, as pound scales, if the field of gravity differs.

 

[Walter]

They won't recalculate the Metric equations, because they know they are on the Moon.

Please explain how scales know they are on the moon.

And a balance scale has the same result regardless of the strength of the field of gravity the device is experiencing.

Exactly, therefore a balance will give the correct result when you are determining mass (kg or slugs), but when you are measuring weight (lbs or newtons) the result will be incorrect. Mass does not change depending on gravity, but weight does.

 

[Blackwood]

What Walter is saying is this:

Take a bathroom scale. Adjust it such that that rather than displaying the applied force, it displays the applied force divided by gravitational acceleration. Now it's 'calibrated for mass'.

If you take it somewhere with a different gravitational acceleration, it will correctly register force, but will divide by the wrong acceleration in displaying mass.

Simple math to illustrate his point:

Assume someone on the surface of the Earth weighs 100 Newtons, and that gravitational acceleration is 9.8m/s².

F=ma, so m=F/a
m=100N/9.8m/s² , where N=kgm/s²
m=10.2kg

Someone with a mass of 10.2kg weighs 100N on the surface of the earth. Take that person to the moon, where the acceleration of gravity is approximately 1.6m/s².

F still = ma
F=10.2kg*1.6m/s²
F=16.3N

Someone with a mass of 10.2kg weighs 16.3N on the moon. It would have been simpler to divide 100N by 6 directly, but might as well show the full thing.

That bathroom scale works by virtue of applied force. If you push on it with a force 100N, it registers 100N. To calibrate it for mass, it must divide by the acceleration of gravity. But if your weight scale divides by 9.8 in order to display mass on the surface of the earth, it's miss-calibrated for the moon. It will divide that 16.3N force it feels by 9.8, displaying a mass of 1.7kg (there's that 1/6 again).

 

[inventor]

Please explain how scales know they are on the moon.

Really? Did you not get that?:shocked2:

 

[Crowley]

I'm glad there's some people in here with a basic grasp of physics.

Ignoring slugs and pounds which are relevant mostly only to the US these days (even the people who invented the imperial system - the British - have mostly abandoned it)

Mass is the measurement of the amount of stuff in an object
Weight is the measurement of the force that the stuff exerts on other stuff because of gravity.

The SI unit of mass is the kilogram. The SI unit of force is the Newton. On planet earth, we use the kilogram as a measurement of mass and weight interchangeably - ie 1 kg of mass weighs 1kg on planet earth. On the moon, 1kg of mass would weigh 1/6th of a kilogram, but its mass is still 1kg. Local gravitational variations are so minute that any deviation is basically meaningless.

If I take a tank which weighs ten kilos, half-fill it with 20 litres of fresh water (which weighs 20 kilos), and add a 5 kilo block of something then as long as no water is spilled, the whole system now weighs 35 kilos. It has 35 kilos of mass on planet earth.

The object in the water tank will appear to weigh less if measured, because of the opposing buoyant force of the water. Take a non-electric scale and sit on it next time you have a bath - you will weigh less, depending on how fat you are. If you weigh 75kgs under normal circumstances, you will still have 75kgs of mass, but you will appear to weigh - let's say - 65kgs.

In large systems, the differences are irrelevant but consider this - every day, millions of people jump into the ocean to swim, dive, bathe, wash clothes. Add to this the combined tonnage of every ship on the planet. We have, without even thinking about it, contributed to a very small but measurable rise in global coastal sea levels.

Have fun with your buoyancy control,

C.

 

[inventor]

Ok, I'm thinking about starting a Wolfgang Pauli thread.

"This isn't right. This isn't even wrong."

Such as, I grew up in a place where it was understood that ice evaporated. (Hang wet clothes out to dry in winter, check for dryness by placing hands together, with the cloth in between. Hint: They dry faster if it's snowing.) But it was also commonly accepted that warm water froze before cold water. (It doesn't.)

Not trolling, just curious. The thread would be, post something that seems non-sensical, such as halocline, fresh water and salt water don't like to mix, but is true. You would also be encouraged to post something like the airplane won't take off thing, that might seem sensible, but isn't.

So, wadda ya think?

 

[smellzlikefish]

Inventor, to modify your quote:

"I don't know what you are saying. I don't think even you know what you are saying."

Ice evaporating is called sublimation, warm water does not freeze before cold water, haloclines exist for the reason you specified (not nonsensical), and airplanes do take off. Please explain what the heck you are trying to say and more importantly, how it even remotely relates to what we are discussing.

 

[inventor]

My bad, thread hijack was inappropriate. I know what sublimation is, do you know why it works faster if the conditions for snow are prevalent?

I'll quit the a**hattery for the day.

 

[smellzlikefish]

Inventor-I didn't mean to bash you but more poke a little fun at your apparently random reply.

 

[naick]

Inventor, to modify your quote:

"I don't know what you are saying. I don't think even you know what you are saying."

Ice evaporating is called sublimation, warm water does not freeze before cold water, haloclines exist for the reason you specified (not nonsensical), and airplanes do take off. Please explain what the heck you are trying to say and more importantly, how it even remotely relates to what we are discussing.

There are specific circumstances where warm water does freeze before colder water.

My bad, thread hijack was inappropriate. I know what sublimation is, do you know why it works faster if the conditions for snow are prevalent?

I don't really know this, but my guess would be the lower pressure, bringing it closer to it's triple point. My other guess would be it's related to the theta-w.