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Water, Air, Steel

ValeryOchkov
24-Ruby IV

Water, Air, Steel

Air-Steel-Water.png

87 REPLIES 87

Ball.png

I believe your center scale should read 35.6 gm.  The ball raises the pressure head the same as the right scale.

The center scale should read 0+30=30gm. Not 35.6 gm.

The ball raises the pressure head the same as the right scale, therefore, the center scale should read 5.6 gm+(30-5.6) gm=30 gm. The second 5.6 gm is the buoyancy force of sphere volume.

LucMeekes
23-Emerald III
(To:ttokoro)

You're both wrong.

 

It is not 35.6 gm, and also not 30 gm.

 

The scale reads 30 g.

The scale measures mass, by determining the weight and correcting for the Earth's gravity factor 9.80665.

 

Luc

ttokoro
20-Turquoise
(To:LucMeekes)

I can't understand your reply.

image.png. Why weight has m/s^2 unit.

In Mathcad, .image.png

If I am wrong, you mean Valely also wrong. He also shows center weight is 30 gm. 

This is the answer of nature.

LucMeekes
23-Emerald III
(To:ttokoro)

My Mathcad Prime says:

LucMeekes_2-1598437548610.png

and

LucMeekes_3-1598437564263.png

if I use it correctly.

 

I know that g is a unit of mass, being 1 kg/1000, it is defined like that in ISO 80000-1.

The prefix k means 1000, so 1/1000 part of 1 kg gives you 1 g.

The Earth's gravitation at sea level is (defined at?) 9.80665 m/s^2, the symbol g is often used for that value.

Note that there is a difference between g and g.

 

The unit of length is m and 1 km is 1000 m.

According to common rules Nm is often used as a unit of torque: N*m. Likewise gm can be understood as g*m, that's not a unit of mass, and not a unit of force.

Using gm instead of g as a unit of mass should be avoided.

 

Luc

 

 

ttokoro
20-Turquoise
(To:LucMeekes)

I well understand what you mean. Using Prime 6, the unit g is 9.8 m/s^2  and gm is 0.001 kg.

These replies are start from Valery's figure and it shows 30 gm instead of 30 g. Then I followed his unit for the weight.

 Any way, our answer is same. The center scale shows 30 g. (or Using Prime 6 it is 30 gm.)

Tokoro.

The scale reads 30 g.

The scale measures mass, by determining the weight and correcting for the Earth's gravity factor 9.80665.

 

Hmmm!   A screen shot from Prime 4.0 Express:  

 
LucMeekes
23-Emerald III
(To:Fred_Kohlhepp)

I see, you want to see the sheet.

LouP
10-Marble
(To:LucMeekes)

Luc,

 

Please post pdf version. I don't have Prime.

 

Thanks,

Lou

Fred_Kohlhepp
23-Emerald I
(To:LouP)

FredKohlhepp_0-1598462660841.png

Luc is taking advantage of Prime's confusing habit of allowing a constant (the g in gravity, the left example), a unit (the g defined as kg/1000,) and several other types:

FredKohlhepp_1-1598462823718.png

This "feature" has caused a lot of pain and confusion . . (IMHO!)

LucMeekes
23-Emerald III
(To:LouP)

I'll save you the trouble of firing up Acrobat or another PDF reader.

Here's the picture of the contents:

LucMeekes_0-1598462890966.png

 

Luc

 

So now you're channeling Val?

 

I didn't doubt you, just pointing out that Prime did not (natively) recognise "g" as a unit for gram.

 

 

LucMeekes
23-Emerald III
(To:LouP)

Here's the experiment for the left side.

I took the same beaker and the same kitchen weigher.

Then I grabbed the blue ball that floats in my garden pond, a small plastic bag and a circular and a strong magnet (I don't want to glue something inside the beaker, I decided to let two magnets hold the bag with the ball under water)...

In short: this stuff:

20200823_125941.jpg

I poured water in the beaker, dropped all the stuff on the weigher and set it to 0.

20200823_125339.jpg

Then I put the strong magnet inside the plasic bag (with the ball) and drowned it. The magnets keep each other together, keeping the ball and plastic bag fully under water. I expected no difference in weight and got this:

20200823_125446.jpg

No difference in weight, as expected. Now my weight scale isn't capable of weighing the amount of air entrapped inside the ball (and there's still some in the plastic bag). I expect however that even if I could measure that, I would see no difference because, per my former reasoning: air remains suspended in air (instead of dropping on the floor or floating to the ceiling).

This leads me to the conclusion that the left side weight is that of only the water, that is:

LucMeekes_0-1598183408245.png

Luc

 

A very nicely designed experiment!  But I have one objection (and one suggestion.)

 

The objection (more an observation):

FredKohlhepp_0-1598190059842.png

With the ball floating on top of the water the ball is partially submerged; this raises the water level (see Val's note.)  Better to weigh the ball outside the beaker.

 

And the suggestion:  substitute a block of wood for the ball of air.  The block should be big enough that the scale can recognize it.  We should be able to see any difference submerging it causes.

 

Kudos for this:

 

"One measurement is worth a thousand expert opinions."

                                                                                            Igor Sikorsky

Now, FredKohlhepp (Sapphire III) concludes his answer. That's the same as my 08-09-2020 10:38 AM post.

LucMeekes (Sapphire II) also finds his answer.

The answer of this puzzle is ValeryOchkov's answer sheet, Air Steel Water End.mcdx.

This is exactly the same as my final answer already posted.

Some differences come from the buoyancy force of the air.

If the density of water and air is the same, it is easy to understand that the weight must be zero.

So using the same density value for air and water, the answers that don’t show zero are wrong for each side.

 

Right side is heavier 0.13847 N.

 

Tokoro.

 

I pedlagayu raise our glasses and drink to the correct solution of the problem!

Cherry.png

ttokoro
20-Turquoise
(To:ValeryOchkov)

My last puzzle of this topic is that why we have no advice from Werner_E, the No.1 specialist of Mathcad community.

 

image.png

 

 

 

image.png

 

 

image.png

Thats not a puzzle but rather a matter of "Cobbler, stick to your last." I followed the thread and its up and downs with great interest 😉

And I'm sure not No.1, there are a lot of collabs here with more experience and knowledge.

The definition and use of "kgf" does nothing good; it merely compounds and extends the confusion that began with the English unit system inherited definitions for force and mass.  Please revert to the true MKS system and use Newtons and kilograms.

Sorry, we have not MKS in Prime - only SI, CGS and USCS.

 

My bad!

 

MKS (from Wikipedia) is units system based on meter/kilogram/second units.  (CGS is centimeter/gram/second)

 

I think PTC refers to it as "SI", it's what my Primes open by default.

LucMeekes
23-Emerald III
(To:Fred_Kohlhepp)

U think MKS is, or at least can be seen as, a predecessor of the SI.

 

Luc

Archimedes' last law:

The fatter I get, the cheaper it is for me to take a bath.

Arh.png

Everyone knows that a kilogram of feathers is heavier than a kilogram of iron. After evacuating the room, that is.

You will laugh, but the weight of one kilogram of iron is more than the weight of one kilogram of wood.

Weight is the force with which an object acts on the scale.

Gravity is mass times the acceleration of gravity.

Weight.png


@ValeryOchkov wrote:

You will laugh, but the weight of one kilogram of iron is more than the weight of one kilogram of wood.

Weight is the force with which an object acts on the scale.

I know you mean the other way around, but let me have the pleasure to correct you 🙂

 

And the second line should end with "corrected for buoyancy"- for clarity.

 

All the best/всего хорошего

LucMeekes
23-Emerald III
(To:ValeryOchkov)

Which (once more) illustrates that weight is a concept that should be approached with care.

Compare the weights of the same blocks of wood and iron:

- in air,

- in vacuum, and

- under water.

 

Luc

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