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Author Topic: why are some things measured in grammes and others in litres?  (Read 7917 times)

paul.fr

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my bottle of coke is 500ml, the big bottle is a litre. the baking soda is 170 grammes, and wasp spray is 300ml. why are they different, why not measure them all in litres?
« Last Edit: 09/06/2007 23:15:48 by paul.fr »


 

Offline laird rob

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why are some things measured in grammes and others in litres?
« Reply #1 on: 09/06/2007 23:29:40 »
liquids are mainly measured in ml and solids usually measured by there weight - eg grammes.

baking soda is a solid.
 

Offline daveshorts

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why are some things measured in grammes and others in litres?
« Reply #2 on: 10/06/2007 00:20:31 »
If something is a liquid it is easy to measure it's volume accurately, you just pour it into a measuring cylinder, a solid will not allways lie flat, things like rice can be differently densely packed, so you have to weigh them, which involves slightly more expensive equipment.
 

Offline Bored chemist

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why are some things measured in grammes and others in litres?
« Reply #3 on: 10/06/2007 10:41:03 »
They are 2 different units because they measure 2 different things.
The litre bottle of coke contains a bit over 1 Kg. If you heat it the volume will change but the mass won't (give or take a tiny contribution from relativity).
 

lyner

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why are some things measured in grammes and others in litres?
« Reply #4 on: 13/06/2007 23:09:21 »
And why are chemists so keen on the dm cubed? It's only the volume of a 10cm cube and much harder to write than an l for litre.
 

Offline eric l

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why are some things measured in grammes and others in litres?
« Reply #5 on: 14/06/2007 11:48:28 »
And why are chemists so keen on the dm cubed? It's only the volume of a 10cm cube and much harder to write than an l for litre.
If my memory does not fail me in this, the definition of the litre is "the volume of 1 kg of pure water at 4C".  There is also the Mohr litre, which is temperature dependent because it is the volume of 1 kg of water at that temperature.
This makes the dm more a primary unit than the litre.
 

Offline eric l

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why are some things measured in grammes and others in litres?
« Reply #6 on: 14/06/2007 12:05:04 »
It is a simple rule to use liters and milliliters for liquids, and kg and g for solids or powders.
In practice however, powders are often measured in volumes, and not just in the kitchen (a spoonful of sugar, a cup of rice...).  In industrial installations, it is sometimes more feasible because weighing is often sensitive to vibration and/or other disturbing factors.  (Less so in modern installations using loadcells rather than balances).
On the other hand, in the lab we often used to weigh the amount of highly viscous or sticky liquids when adding them to a mixture.
 

Offline Bored chemist

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why are some things measured in grammes and others in litres?
« Reply #7 on: 14/06/2007 19:07:40 »
And why are chemists so keen on the dm cubed?
Because it's a proper SI unit (ok, perhaps it should be refered to as a mili cubic metre)and, perhaps more importantly,
Because it isn't the same volume as a litre.
 

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why are some things measured in grammes and others in litres?
« Reply #7 on: 14/06/2007 19:07:40 »

 

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