You're in a rowboat in a pool and there is a concrete block in the boat.
You drop the block into the water. Does the water level in the pool go up,
down or remain the same?

Most people here will get this but most "normal" people won't.

The water level in the pool goes down.
Paul K. Dickman

Tom Gardner wrote in message ...
You're in a rowboat in a pool and there is a concrete block in the boat.
You drop the block into the water. Does the water level in the pool go up,
down or remain the same?

Most people here will get this but most "normal" people won't.

Paul K. Dickman wrote:

Tom Gardner wrote in message ...
You're in a rowboat in a pool and there is a concrete block in the boat.
You drop the block into the water. Does the water level in the pool go up,
down or remain the same?

Most people here will get this but most "normal" people won't.

The water level in the pool goes down.

Unless it's a pool of mercury.

On Thu, 18 Dec 2003 17:58:38 GMT, "Tom Gardner" wrote:
You're in a rowboat in a pool and there is a concrete block in the boat.
You drop the block into the water. Does the water level in the pool go up,
down or remain the same?

The water level goes down. That's because the boat has to displace an
amount of water equal to the weight of the concrete, while the concrete
itself only has to displace an amount of water equal to its volume. Since
concrete has a higher density than water, it displaces less water sunk
than when floated in a boat.

Gary

Ian Stirling wrote: Unless it's a pool of mercury.
^^^^^^^^^^^
I wouldn't eat the fish from that pool.
Since mercury is a metal, this thread is no longer OT.

You didn't specify whether or not Lacy was attached.
JR
Dweller in the cellar

Tom Gardner wrote:

You're in a rowboat in a pool and there is a concrete block in the boat.
You drop the block into the water. Does the water level in the pool go up,
down or remain the same?

Most people here will get this but most "normal" people won't.

--
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--------------------------------------------------------------
Dependence is Vulnerability:

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Naw, Gary! The concrete would cause the water level to rise so rapidly, the
resulting wave would swamp the boat causing further water level rise, which
would swamp the boat, . . . causing further water level rise, ad nauseum.
At peril to repetition of Noah's Ark incident, please don't try this
experiment!!

Bob Swinney
"Gary Coffman" wrote in message
...
On Thu, 18 Dec 2003 17:58:38 GMT, "Tom Gardner" wrote:
You're in a rowboat in a pool and there is a concrete block in the boat.
You drop the block into the water. Does the water level in the pool go
up,
down or remain the same?

The water level goes down. That's because the boat has to displace an
amount of water equal to the weight of the concrete, while the concrete
itself only has to displace an amount of water equal to its volume. Since
concrete has a higher density than water, it displaces less water sunk
than when floated in a boat.

Gary

Tom Gardner wrote:

You're in a rowboat in a pool and there is a concrete block in the boat.
You drop the block into the water. Does the water level in the pool go
up,
down or remain the same?

Most people here will get this but most "normal" people won't.

Lets make it a little more complicated. Suppose the concrete block is
attached to the boat with a rope. When you throw it overboard, it
hangs from the boat rather than goes to the bottom of the pool.

Does the water level in the pool go up, down or remain the same?

Pete.

Peter Reilley wrote:

Tom Gardner wrote:


You're in a rowboat in a pool and there is a concrete block in the boat.
You drop the block into the water. Does the water level in the pool go


up,


down or remain the same?

Most people here will get this but most "normal" people won't.



Lets make it a little more complicated. Suppose the concrete block is
attached to the boat with a rope. When you throw it overboard, it
hangs from the boat rather than goes to the bottom of the pool.

Does the water level in the pool go up, down or remain the same?

How big is the rope?
Ken

"Ken Vale" wrote in message
.cable.rogers.com...
Peter Reilley wrote:

Tom Gardner wrote:


You're in a rowboat in a pool and there is a concrete block in the
boat.
You drop the block into the water. Does the water level in the pool go


up,


down or remain the same?

Most people here will get this but most "normal" people won't.



Lets make it a little more complicated. Suppose the concrete block is
attached to the boat with a rope. When you throw it overboard, it
hangs from the boat rather than goes to the bottom of the pool.

Does the water level in the pool go up, down or remain the same?

How big is the rope?
Ken


For this purpose, the rope is infinitely thin and weightless.

For extra credit, consider the condition where the rope has neutral
buoyancy.

Pete.

Peter Reilley wrote: For this purpose, the rope is infinitely thin and
weightless. For extra credit, consider the condition where the rope has
neutral buoyancy.
^^^^^^^^^^^^
A boat floats in the water at a depth at which it displaces its own weight
of water. The shape of the hull does not change this fact. When you tie
the concrete block to the boat, in effect you are making it part of the
boat. When you throw the block and rope into the water, you have, in
effect, changed the shape of the hull, without changing its weight, so the
amount of water displaced does not change. Therefor, the pond level does
not change. Making the rope "weightless" or of neutral buoyancy does not
make any difference. The water level does not change.

"Leo Lichtman" wrote in message
...
Peter Reilley wrote: For this purpose, the rope is infinitely thin and
weightless. For extra credit, consider the condition where the rope has
neutral buoyancy.
^^^^^^^^^^^^
A boat floats in the water at a depth at which it displaces its own weight
of water. The shape of the hull does not change this fact. When you tie
the concrete block to the boat, in effect you are making it part of the
boat. When you throw the block and rope into the water, you have, in
effect, changed the shape of the hull, without changing its weight, so the
amount of water displaced does not change. Therefor, the pond level does
not change. Making the rope "weightless" or of neutral buoyancy does not
make any difference. The water level does not change.


I believe that we have a correct answer.

Pete.

Peter Reilley wrote:

When you throw the block and rope into the water, you have, in
effect, changed the shape of the hull, without changing its weight, so the
amount of water displaced does not change. Therefor, the pond level does
not change. Making the rope "weightless" or of neutral buoyancy does not
make any difference. The water level does not change.



I believe that we have a correct answer.


What's interesting is the boat would ride higher in the water but the
level in the tank would remain the same.




--

Mark

N.E. Ohio


Never argue with a fool, a bystander can't tell you apart. (S. Clemens,
A.K.A. Mark Twain)

When in doubt hit the throttle. It may not help but it sure ends the
suspense. (Gaz, r.moto)

Mark wrote:


Peter Reilley wrote:

When you throw the block and rope into the water, you have, in

effect, changed the shape of the hull, without changing its weight,
so the
amount of water displaced does not change. Therefor, the pond level
does
not change. Making the rope "weightless" or of neutral buoyancy does
not
make any difference. The water level does not change.



I believe that we have a correct answer.



What's interesting is the boat would ride higher in the water but the
level in the tank would remain the same.




--

Mark

N.E. Ohio


Never argue with a fool, a bystander can't tell you apart. (S. Clemens,
A.K.A. Mark Twain)

When in doubt hit the throttle. It may not help but it sure ends the
suspense. (Gaz, r.moto)

Ok I am confused by all these wanna be wet blocks . A block in water
will displace its volume regardless of its mass . But in the boat it
displaces its equal mass of water . Which is greater . So hanging off a
rope attached to a boat displacing already its volume but pulling down
on the boat additionally displacing its mass ? So what is the point of
all this ? Attempting starting your own artificial reefs ? Trying to
hide blocks in case the world ends tomorrow and there might be a
shortage ? Stockpiling and hoping the value of blocks increases ? Try
cornering the block market ? Maybe try spiking the eggnog less ? More ?

Ken Cutt

On Sat, 20 Dec 2003 03:28:16 -0800, Ken Cutt wrote:
Ok I am confused by all these wanna be wet blocks . A block in water
will displace its volume regardless of its mass . But in the boat it
displaces its equal mass of water . Which is greater .

Actually, in the boat it displaces its *weight*, not mass, but otherwise
correct.

So hanging off a
rope attached to a boat displacing already its volume but pulling down
on the boat additionally displacing its mass ?

It displaces its volume, which applies some bouyant force to the
block. This offsets some of its *weight* (not the same thing as mass),
so its full weight isn't pulling down on the boat. The net result is that
there's no change in the total amount of water displaced, regardless
of whether the block is in the boat or suspended in the water below it.

So what is the point of
all this ?

The point is that it isn't intuitively obvious what will happen in these
situations. You have to be able to think rationally about the physics
to get the right answer. So it is really a test of your knowledge of
physics, and your ability to think rationally.

Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.

Gary

Ken Cutt wrote: (clip) So what is the point of all this ? (clip)
^^^^^^^^^^^^^
OK, Ken, if you need to know the motivation of the characters in order to
enjoy the problem, then think about this one. It has the additional
advantage that it is metal related, so, not OT.

A blacksmith is forging a knife blade, on board a boat. When he is ready to
quench the red hot steel, he hangs it over the side from a piece of wire.
As the steel goes into the water, of course, it cools, so it gets smaller.
It also produces a lot of steam bubbles. What happens to the water lever as
all this takes place?

To keep the answer on topic, the water level doesn't change, give or take
a few thousandths _tolerance_. ;-) BTW you didn't say how wide the
container is, nor the blade.

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"Leo Lichtman" wrote in message
...

Ken Cutt wrote: (clip) So what is the point of all this ? (clip)
^^^^^^^^^^^^^
OK, Ken, if you need to know the motivation of the characters in order to
enjoy the problem, then think about this one. It has the additional
advantage that it is metal related, so, not OT.

A blacksmith is forging a knife blade, on board a boat. When he is ready
to
quench the red hot steel, he hangs it over the side from a piece of wire.
As the steel goes into the water, of course, it cools, so it gets smaller.
It also produces a lot of steam bubbles. What happens to the water lever
as
all this takes place?

Tim Williams wrote:

BTW you didn't say how wide the
container is, nor the blade.

Or the mass of the blade, its composition, and the delta-T. g

-- Mark

It got soaked up in that funny cigarette you threw in?

Bob Swinney
"Leo Lichtman" wrote in message
...

Ken Cutt wrote: (clip) So what is the point of all this ? (clip)
^^^^^^^^^^^^^
OK, Ken, if you need to know the motivation of the characters in order to
enjoy the problem, then think about this one. It has the additional
advantage that it is metal related, so, not OT.

A blacksmith is forging a knife blade, on board a boat. When he is ready
to
quench the red hot steel, he hangs it over the side from a piece of wire.
As the steel goes into the water, of course, it cools, so it gets smaller.
It also produces a lot of steam bubbles. What happens to the water lever
as
all this takes place?

Gary Coffman wrote:

Actually, in the boat it displaces its *weight*, not mass, but otherwise
correct.

Unless the boat and block are in different gravitational fields, the
result is the same. W=mg.

Ted

Gary Coffman wrote:


Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.

Gary

How is "a metric ton mass" defined ?

...lew...

Gary Coffman wrote:

Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.


Good Christ, you have to do better than that.


My 3rd or 4th grade teacher asked us that one.



--

Mark

N.E. Ohio


Never argue with a fool, a bystander can't tell you apart. (S. Clemens,
A.K.A. Mark Twain)

When in doubt hit the throttle. It may not help but it sure ends the
suspense. (Gaz, r.moto)

On Sun, 21 Dec 2003 04:05:16 GMT, Lewis Hartswick wrote:
Gary Coffman wrote:

Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.

Gary

How is "a metric ton mass" defined ?

A metric ton is 1000 kilograms, mass not weight. Mass is a
measure of inertia, which is a fundamental property of matter.
Weight is a force, which isn't a fundamental property of
matter.

Gary

On Sun, 21 Dec 2003 04:05:57 GMT, Mark wrote:
Gary Coffman wrote:

Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.


Good Christ, you have to do better than that.

Ok, the feathers and lead are hanging from the opposite arms
of a balance. Which side goes down? Better?

Gary

Gary Coffman wrote:

On Sun, 21 Dec 2003 04:05:57 GMT, Mark wrote:

Gary Coffman wrote:


Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.


Good Christ, you have to do better than that.


Ok, the feathers and lead are hanging from the opposite arms
of a balance. Which side goes down? Better?


I remember now.

It was third grade.

Mrs. Cummings would be giving you the evil eye.




--

Mark

N.E. Ohio


Never argue with a fool, a bystander can't tell you apart. (S. Clemens,
A.K.A. Mark Twain)

When in doubt hit the throttle. It may not help but it sure ends the
suspense. (Gaz, r.moto)

Gary Coffman wrote:
On Sat, 20 Dec 2003 03:28:16 -0800, Ken Cutt wrote:

Ok I am confused by all these wanna be wet blocks . A block in water
will displace its volume regardless of its mass . But in the boat it
displaces its equal mass of water . Which is greater .


Actually, in the boat it displaces its *weight*, not mass, but otherwise
correct.


So hanging off a
rope attached to a boat displacing already its volume but pulling down
on the boat additionally displacing its mass ?


It displaces its volume, which applies some bouyant force to the
block. This offsets some of its *weight* (not the same thing as mass),
so its full weight isn't pulling down on the boat. The net result is that
there's no change in the total amount of water displaced, regardless
of whether the block is in the boat or suspended in the water below it.


So what is the point of
all this ?


The point is that it isn't intuitively obvious what will happen in these
situations. You have to be able to think rationally about the physics
to get the right answer. So it is really a test of your knowledge of
physics, and your ability to think rationally.

Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.

Gary

Gary
Well all I did was pose a few questions and a few tongue in cheek
comments . I did not take any physics in school . Age of the mini skirt
and ban the bra bunch ;-). So my attention was some what diverted much
of the time . Now about the lead and feathers . You didn't mention if
they were from Europeon or African Swallows ? Now as tempting as it
might be to say they are the same getting a wrong answer means the
bridge troll wins again and I probably would end up near a boat smashed
up on an artificial reef complete with a blacksmith , forge and a well
quenched knife .
Ken Cutt

On Sun, 21 Dec 2003 03:24:02 GMT, Ted Edwards wrote:
Gary Coffman wrote:

Actually, in the boat it displaces its *weight*, not mass, but otherwise
correct.

Unless the boat and block are in different gravitational fields, the
result is the same. W=mg.

No. 'W' is a force. 'M' is the measure of inertia of a body.
'W' is vector, 'M' is scalar. They aren't the same.

Gary

On Sun, 21 Dec 2003 05:53:36 GMT, Mark wrote:
Gary Coffman wrote:

On Sun, 21 Dec 2003 04:05:57 GMT, Mark wrote:

Gary Coffman wrote:


Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.


Good Christ, you have to do better than that.


Ok, the feathers and lead are hanging from the opposite arms
of a balance. Which side goes down? Better?


I remember now.

It was third grade.

Mrs. Cummings would be giving you the evil eye.

Probably because she didn't realize that air, like water, exerts
a bouyant force.

Gary

Gary Coffman wrote:

On Sun, 21 Dec 2003 04:05:16 GMT, Lewis Hartswick wrote:
Gary Coffman wrote:

Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.

Gary

How is "a metric ton mass" defined ?

A metric ton is 1000 kilograms, mass not weight. Mass is a
measure of inertia, which is a fundamental property of matter.
Weight is a force, which isn't a fundamental property of
matter.

Gary

OK I just have never seen the term "ton" used with "mass" problems.
Then it's obvious that equal masses of two different density matls.
will have different volumes and hence bouyant forces due to air
displaced.
...lew...

In article , Gary Coffman says...

'W' is vector, 'M' is scalar. They aren't the same.

But you have to be pretty smart to
understand why they *look* the same.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

In article , Gary Coffman says...

Ok, the feathers and lead are hanging from the opposite arms
of a balance. Which side goes down? Better?

OK the balance that has both is in air, right?

But how did you determine the original 1 metric ton
number? If you put each of the items on a scale,
in air, and added or subtracted lead/feathers until
the number said "one" each time, then the
balance will stay zeroed when you compare the
two directly.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

On Sat, 20 Dec 2003 03:28:16 -0800, Ken Cutt
wrote:

Mark wrote:


Peter Reilley wrote:

When you throw the block and rope into the water, you have, in

effect, changed the shape of the hull, without changing its weight,
so the
amount of water displaced does not change. Therefor, the pond level
does
not change. Making the rope "weightless" or of neutral buoyancy does
not
make any difference. The water level does not change.



I believe that we have a correct answer.



What's interesting is the boat would ride higher in the water but the
level in the tank would remain the same.

Wow! So if I unclamp my outboard motor, tie a rope to it and toss it
overboard, then I'll ride higher in the water so I can cast further!

Gary Coffman wrote:

Gary Coffman wrote:
Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?

A metric ton is 1000 kilograms, mass not weight. Mass is a
measure of inertia, which is a fundamental property of matter.
Weight is a force, which isn't a fundamental property of
matter.

Actually, the SI unit of weight is the Newton in spite of the fact that
some folk use Kilogram-weight, approx. 9.8Newtons.

Since you said "weighs" not "masses", the lead weighs more. Although
the difference is small, there is a slight bouyancy effect since air is
not massless and the amount of air displaced is larger for the feathers.

Ted

Mark wrote:

Good Christ, you have to do better than that.

My 3rd or 4th grade teacher asked us that one.

Careful now. There is a subtelty here. Hint: In air, not vacuum.

Ted

Gary Coffman wrote:

Unless the boat and block are in different gravitational fields, the
result is the same. W=mg.

No. 'W' is a force. 'M' is the measure of inertia of a body.
'W' is vector, 'M' is scalar. They aren't the same.

Re-read my post. I did not say weight and mass are the same. I said
the _result_ was the same. Indeed, mass is a scalar and, in a uniform
gravitational field, g is a vector thus so is W. However, under
appropriate circumstances, g may be a tensor.

Ted

On Sun, 21 Dec 2003 04:05:16 GMT, Lewis Hartswick wrote:
Gary Coffman wrote:


Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.

Gary

How is "a metric ton mass" defined ?

1000 kg

--
"It's easier to find people online who openly support the KKK than
people who openly support the RIAA" -- comment on Wikipedia
(Email: , but first subtract 275 and reverse
the last two letters).

On Sat, 20 Dec 2003 15:58:39 -0500, Gary Coffman wrote:

Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?
Think carefully.

The lead; it is less bouyant in air.

--
"It's easier to find people online who openly support the KKK than
people who openly support the RIAA" -- comment on Wikipedia
(Email: , but first subtract 275 and reverse
the last two letters).

On Sat, 20 Dec 2003 23:46:28 -0500, Gary Coffman wrote:

Ok, the feathers and lead are hanging from the opposite arms
of a balance. Which side goes down?

Deprends on the accuracy (and other properties) of the balance.

--
"It's easier to find people online who openly support the KKK than
people who openly support the RIAA" -- comment on Wikipedia
(Email: , but first subtract 275 and reverse
the last two letters).

On Sun, 21 Dec 2003 18:58:22 GMT, Ted Edwards wrote:
Gary Coffman wrote:
Gary Coffman wrote:
Now, with the knowledge gained from this thought experiment, here's
another brain teaser. Which weighs more (at the Earth's surface, in
air), a metric ton mass of feathers, or a metric ton mass of lead?

A metric ton is 1000 kilograms, mass not weight. Mass is a
measure of inertia, which is a fundamental property of matter.
Weight is a force, which isn't a fundamental property of
matter.

Actually, the SI unit of weight is the Newton in spite of the fact that
some folk use Kilogram-weight, approx. 9.8Newtons.

Correct. In the Imperial system, the pound is a unit of force, the
slug is the unit of mass. In either case, weight is a force, not a
mass.

Since you said "weighs" not "masses", the lead weighs more. Although
the difference is small, there is a slight bouyancy effect since air is
not massless and the amount of air displaced is larger for the feathers.

Correct.

Gary

On 21 Dec 2003 07:54:12 -0800, jim rozen wrote:
In article , Gary Coffman says...

Ok, the feathers and lead are hanging from the opposite arms
of a balance. Which side goes down? Better?

OK the balance that has both is in air, right?

But how did you determine the original 1 metric ton
number? If you put each of the items on a scale,
in air, and added or subtracted lead/feathers until
the number said "one" each time, then the
balance will stay zeroed when you compare the
two directly.

Right. The balance is only comparing moments,
ie torques, ie force times distance. In air (or water)
the force is dependent on other things besides
mass. So you can't accurately measure mass that
way.

Remember that mass is a measure of inertia, so to
measure it properly, you have to make some sort
of measurement which depends solely on the inertial
properties of the body you're measuring.

Gary