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Author Topic: 'what's heavier, me or water?' - Now: weight vs density?  (Read 10602 times)

Offline anotheriain

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I was recently asked by a child, 'What's heavier, me or water?' Assuming the full question is 'What's heavier, me or an exact-size copy of me made of water?', what is the answer? And, to anticipate the follow-up question, why?...
« Last Edit: 08/03/2009 23:34:01 by anotheriain »


 

lyner

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Re: 'what's heavier, me or water?' - Now: weight vs density?
« Reply #1 on: 07/03/2009 21:15:11 »
You, or your density, is just less than that of water - that's why you float in water.
 

Offline Madidus_Scientia

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Re: 'what's heavier, me or water?' - Now: weight vs density?
« Reply #2 on: 08/03/2009 02:22:06 »
That would depend on how much air is in your lungs at the time though

If you squeeze it all out you sink, well I do anyway
 

Offline Chemistry4me

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Re: 'what's heavier, me or water?' - Now: weight vs density?
« Reply #3 on: 08/03/2009 02:56:20 »
How do you manage to squeeze it all out? ???
 

Offline Astronomer_FB

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Re: 'what's heavier, me or water?' - Now: weight vs density?
« Reply #4 on: 08/03/2009 03:03:51 »
How do you manage to squeeze it all out? ???
next time you are in a pool become really compact and then go under water at first you float then blow out the air you have in your lungs and you will start to sink.
 

Offline Chemistry4me

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Re: 'what's heavier, me or water?' - Now: weight vs density?
« Reply #5 on: 08/03/2009 03:06:04 »
It'll be impossible to get all of it out!
 

Offline JnA

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Re: 'what's heavier, me or water?' - Now: weight vs density?
« Reply #6 on: 08/03/2009 03:41:34 »
an exact you made of water would be the same density as.. well water. You however, not completely made of water, have air cavities and bone that is made of holes... even a non breathing human floats.... eventually
 

Offline yor_on

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Re: 'what's heavier, me or water?' - Now: weight vs density?
« Reply #7 on: 08/03/2009 11:07:19 »
Tell him that when he was in his Mummy's tummy:) he was floating freely (for a while). So in there it seems we have the correct density, and I've read somewhere that this density is very near saltwater (the oceans). It was used as one of the proofs that we come from the sea originally. That and our females ability to 'cork up' automatically their 'neither regions' as they go into the sea to swim. That's a mechanism not seen in landbased animals normally, according to that source.
 

Offline JP

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Re: 'what's heavier, me or water?' - Now: weight vs density?
« Reply #8 on: 08/03/2009 16:40:53 »
Wikipedia puts the average human body as very slightly denser than water: 1.01 g/cm3 as opposed to 1.00 g/cm3 (pure water at 4C).  That explains why I used to slowly sink in the pool if I exhaled as much air as I could.  Variations in body fat, muscle development, and bone density can probably change that number by enough to make a person more/less dense than pure water.  Salt water, however, is considerably more dense than the human body, so everyone will probably float in the ocean.
 

Offline anotheriain

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Re: 'what's heavier, me or water?' - Now: weight vs density?
« Reply #9 on: 08/03/2009 23:33:12 »
What, then, is the difference between weight and density?
 

Offline Chemistry4me

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'what's heavier, me or water?' - Now: weight vs density?
« Reply #10 on: 09/03/2009 02:43:45 »
I cannot give you a very good definition, but as far as I know: Weight is determined by the mass or quantity of matter as acted on by the force of gravity, that counteracts efforts to lift or move them. Density is a measure of a quantity such as mass or electric charge per unit volume. :)
 

Offline JP

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'what's heavier, me or water?' - Now: weight vs density?
« Reply #11 on: 09/03/2009 15:43:54 »
The exact definitions of weight and density require some other definitions first:

Mass is basically the "amount of stuff" in an object. 
Weight is the reading you get on a scale because gravity pulls on mass.  On the earth's surface, weight and mass are proportional.

Volume is the amount of space an object takes up. 
Density in this context is the amount of mass per unit volume.  Density is  useful because it allows you to compare like-sized chunks of objects and see how much "stuff" is in each of them.

In terms of your original question, things less dense than water will float in it.
 

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'what's heavier, me or water?' - Now: weight vs density?
« Reply #11 on: 09/03/2009 15:43:54 »

 

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