More brain teasers

[Paddy]

I agree with Chris, any rapidly cooled volcanic rock will contain bubbles of air in them making it less dense. In the case of pumice, the air will eventually be displaced from the rock if emersed in water.


or it could be a floater..... yum yum

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I think teaser one is (b) because the weight of the rock will force the boat deeper into the water, more so than the mass of the rock alone.

I think the answer to 2 is a (or a new steady state). As the water pressure increases, then the balloon will get squashed and more air will be allowed to escape from the balloon making its volume smaller.

but then what do i know...

[Jorden]

One thing about this brick in question 2: What is it made of? Sandstone and thus likely to take up a lot of water, therefor sending the balloon to the bottom, or concrete, which doesn't take up too much water, but still will let it plummet to the bottom, or is it granite or marble, both of which don't take up any water that it will have much effect?

Jord.

[cerb]

Okay, next time I'll put post brain teasers that are less ambiguous.

Vlip: Yep, you're thinking of pumice. There's an area around here where there's tons of the stuff.

Chris B: It'd depend on the piece of pumice as to whether it'd absorb enough water or not... cause I'd imagine that there'd be lots of pores all through the rock, most of which would be internal, so the water may not get to them. If so, there'd still be a lot of air in it, so it would still float.

Jorden: I'm not sure exactly what house bricks are made of, but I don't think they absorb too much water (otherwise it'd get wet on the inside of the house after too much rain!

Okay, Teaser #3: (from http://www.brainteaser.net)

A Rebus Puzzle: What phrase or expression is represented below?

<center>G
R
A
N
D
</center>

Cerb

[Jorden]

cerb, ever tried to spray water on your wall, when you were spraying the garden? How much of the water evaporates, how much streams down to the ground, and how much is quickly absorbed by the bricks when you spray the garden again?

You answered my question, which is that it will soak up water a lot and thus fall to the bottom, with the balloon still attached

GRAND: Going Randomly Against Nude Dykes

Jord.

[cerb]

Jorden: I wouldn't go against nude dykes. If they want to be nude, then by all means! As long as it's in a public place, or recorded on video for analysis later.

Cerb

[Chris B]

This rock wasn´t all white and looked like a dried out dogsh**, because you know then it probably was

Seriously though, I think the rock you are talking about might be "pumice". It will in fact float if you throw it in the water, but if you leave it in for a couple of minutes it will absorb water and sink... well "like a stone"!

[FaRaN]

As my hobby is scubadiving, I know the answer to the second puzzle, because I experience it myself. When I stabelise(put air in the jacket (BCD, Bouency Control Device) I have on, with the cilinder on it) at a certain depth, I keep floating on exact position where I'm at. When I swim down, I'll sink further untill I put more air in my BCD to stabelise. This is because the pressure of the water (atmosfere) increases, compresses the air in my BCD (and longs, and cilinder even) what makes me sink. This is the same for the balloon+brick. As the ballon are the BCD and longs, and the brick is a body.

So when you go up. The pressure decreases and the balloon + brick will rise, untill you let some air out.

Very easy. Lesson one in scubadiving!


As for the first question I guess:
The weight of the brick in the boat makes the boat push away water with much more effect than the brick itself, cause the boat's surface is much bigger than the brick's. When the brick is in the water the boat stops pushing away water, is replaced by the brick much less effect. So the lake will rise.

Don't feel like reading it over and over again to perfect my english. I assume you all understand what I'm saying.

[Paddy]

er.. this is the correct url http://www.brainteasers.net/


but i couldn't find that problem there though ...

[Paddy]

Doh!

That's terrible!

What do you mean, you dont get it?

Never watched Catchphrase?

[Chris B]

I did find it, I just don´t get it!

They ought to put some explanations with the answers.

--------------------
No I never watched catchphrase, they don´t show that in Denmark. Any good ??

[This message has been edited by Chris B (edited 29 November 2000).]

[agallag]

cerb, it's GRANDSTAND... obviously

------------------
Andrew
Carpe Cerevisi

[spoogenet]

Damage: Would you mind going back and reading both of your posts?

You said, and I quote, "At no point will the water level increase."

And what I'm saying has nothing to do with the volume of the rock. The rock is the same volume, period, all I'm considering is it's density and, consequently, mass. Go back and read my posts and FaRaN's post and you will realize that the surface area of the boat matters, and when the rock is in the boat it's mass will affect the volume of water displaced, while the rock's volume will not have any effect in the boat. Out of the boat is the only place where the rock's volume matters, however it's mass is of no relevance outside the boat.

b

[agallag]

To clarify: a floating object displaces it's own mass of water, and a submerged object displaces it's own volume of water. For a rock that's more dense than water, it will displace more water when it's floating than it will when it's submerged, therefore the water level will go down measurably when the rock is thrown in the water. This can be tested in a lab with a piece of styrofoam, a small lead weight, and a beaker of water.

Edit: BTW, the measured results have no bearing on the size (or surface area) of the boat.
------------------
Andrew
Carpe Cerevisi

[This message has been edited by agallag (edited 29 November 2000).]

[cerb]

Faran: Cool. Nice to have it clarified once and for all.

Anybody else guessing on the "GRAND" one? Answer coming tomorrow...

Cerb

[damage]

spongenet
would you mind bothering to read my post again
where did i say that a heavy rock (that's heavier than water) doesn't displace more weight in water than it's volume!?
i said that if it's heavy enough to sink the water level decrease
if it's not heavy enough to sink then it must float (duh) and it won't make a difference in or out of the boat
to be specific anything supported by water displaces it's exact weight. ie 1kg rock displaces 1kg of water which is roughly 1L
anyway so bored of this thread