If I know the density of wood, how can I work out the density of water?

Ricochet J

Ricochet J

Ricochet J

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I'm doing some mechanics revision and the paragraph doesn't explain it well, so I was just wondering if anyone would educate me :)

I phoned a mate, and he says one way is, if you've got a wood block, of known length and density, and then put it in water then if the wood block sticks out by half it's length, the density of water is half of that of wood. Likewise, if the wood length sticks out by 2/3 then density of water is 1/3 that of the wood.

Anyone expand on that please? I'm really having no Google luck either :(
 
Put a block of wood in water, the block of wood weights the same as the area of water underwater :)

i.e. if the box is wood, a&b volume of wood == b volume of water
Code: 
     _________
    |       a   |
--------------------
    |____b____|

kind of!
 
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density = mass / volume...

You can just measure the mass of the wood and the amount of water displaced as far as I know. (GSCE physics was a long time ago :p )
 
Ricochet J said:
I'm doing some mechanics revision and the paragraph doesn't explain it well, so I was just wondering if anyone would educate me :)

I phoned a mate, and he says one way is, if you've got a wood block, of known length and density, and then put it in water then if the wood block sticks out by half it's length, the density of water is half of that of wood. Likewise, if the wood length sticks out by 2/3 then density of water is 1/3 that of the wood.

Anyone expand on that please? I'm really having no Google luck either :(
Click to expand...

Archimedes stated that the weight of water displaced by any floating object will be equal to the objects weight.

So if a block of wood floats half in water, half out, then its density is half that of water. If it floats with 9/10's submerged then its density is 9/10ths that of water.
 
johntmanic said:
Im doing Hydraulics at uni and i take the mass of water to be 1000 kg/m3.
Hope that helps?
Click to expand...

Im rather disturbed that a university student doesnt know the difference between mass and density......
 
thats what i meant density.... ha ha ha! sorry dont listen to me ;)

Well density is 1000 kg/m3 for water.... like as the other poster above said anything less than 1000kg/m will float on water i.e. when you see oil slicks this is because oil has a density of around 885kg/m3.
 
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Visage said:
Im rather disturbed that a university student doesnt know the difference between mass and density......
Click to expand...

:confused:

(density) rho = m/V

where

m is the object's total mass ([M]; kg)
V is the object's total volume ([L³]; m³)

kg/m3 sounds right to me.
 
Bill101 said:
the density of water is 1 anything that sinks is higher than 1 anything that floats is lower than one
Click to expand...

The statement you've made in bold is nonsensical without a discussion of what units you are using.
 
AJUK said:
:confused:

(density) rho = m/V

where

m is the object's total mass ([M]; kg)
V is the object's total volume ([L³]; m³)

kg/m3 sounds right to me.
Click to expand...

He stated that the mass of water was 1000 kg/m3. Mass isnt measured in kg/m3.
 
1 gram per mililitre/cm^3 is the density of water, give or take.

You know the density of the object. Work out it's volume and calculate it's weight. Measure the volume of water displaced, you know that it weighs the same as the block. Then divide one by the other.

mass/ volume = density
 
afaik the unit weight of water is, as has been stated, is 1000kg/m3 which was derived by the romans which is the founding for metric weights :rolleyes: anyhoo.

Iirc the theory behind stuff floating is that the mass of the volume of water displaced by an object is the amount of mass that the water can support. if that makes any sense. thats from 4 years ago in my hydraulics theory lectures ;) so it may be slightly wrong :eek:
 
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