corps-étranger

19:03 Mar 17, 2016 

That's because it is only 1/3 immersed! Immersed means inside the liquid, not floating above it. If that solid body is actually immersed (with the aid of BD's toothpick, for example) then it will displace its entire volume.

18:52 Mar 17, 2016 

you said yourself why it's wrong to assume that the French text is wrong:

== As long as it's dense enough to sink! ==

well, if it's not, [which may happen - for example, ships are not supposed to sink ...] the displaced volume of liquid will depend of the volume of the solid body AND of its density (more precisely of its relative density compared to the density of the liquid); a solid body 3 times less dense than the liquid will displace only 1/3 of its volume when immersed.

16:40 Mar 16, 2016 

You theoretically could, but I'd like to see you do it in practice :)

16:36 Mar 16, 2016 

You could hold a cubic cm of polystyrene down using a toothpick, ensuring the tip didn't break the surface, as Archimedes said as he got out of the bath.

16:00 Mar 16, 2016 

The density of the immersed body has nothing to do with it. The level will rise exactly the same amount if you immerse a cubic cm of lead or a cubic cm of something less dense. (As long as it's dense enough to sink!)

12:35 Mar 16, 2016 

Do note that the remainder of your sentence is seriously flawed too, and is neither idiomatic nor natural in EN — as well as being a technically inaccurate translation of the source text!

12:32 Mar 16, 2016 

an immersed solid body seems to fit better.

12:29 Mar 16, 2016 

'foreign body' always suggests 'something that shouldn't be there' — which is not really the case here; I'd personally be inclined to go for just 'body'.

However, I certainly wouldn't use the verb 'plunge'! It has a subjectice and quite energetic connotation that would be out of place here — if you did do any 'plunging', the water would probably splash out all over the lab! I'd definitely suggest using the more neutral, formal, and technical verb 'immerse', just as in FR.

I would also be wary of using 'plunge' later in the sentence too — the meaning (and particualrly connotation) is ever so slightly different between FR and EN.