T
Tom Del Rosso
- Jan 1, 1970
- 0
Martin said:Laws of physics.....
Leftists like to change Laws.
Progressive laws and sustainable technology. Ass backwards.
Martin said:Laws of physics.....
Leftists like to change Laws.
H ow do you define 'pressure differential of the surrounding atmosphere'?
Like starting an upside-down siphon, almost.
I know this isn't the right group for this question, but I want
an answer an electrical engineer can understand.
I understand the simple model of buoyancy. If something weighs
less than the medium it displaces, it floats.
The question is, "why?"
If you stick a ping pong ball under water and let go, it floats.
What's the mechanism? The water has no idea what's inside the
ball. We have water molecules banging into the ball on all sides.
Is there a simple explanation, in layman's terms, of what's actually
going on to force the ball up?
I really want to understand how convection works in a chimney,
but water should be easier to grasp.
That's one of those laws of nature that seems to 'cause' things to happen as
if they understand the law.
Thanks, guys, for the inputs.
Those are the classical arguments. I accept them as true and useful
models for everyday use.
But, I'm still not satisfied.
Throw a sheet of thin plywood into the swimming pool.
If you put sufficient force on it, it sinks.
Now turn it vertical and push it down.
The force to submerge it should not change.
But the direction of force applied by all the molecules banging
on the side do not obviously have a net upward force.
The thing I'm trying to get my brain around is convection.
If I have a 20 foot chimney and build a fire in the firebox,
air gets sucked in the box and goes up the chimney.
If I cut a hole in the bottom and stack it on top of a
similar chimney (close up the front), does the same amount
of air get sucked into the bottom (cold) fireplace?
My intuition says it does.
OK, so now, put an S-curve in the pipe, kinda like a P-trap.
Can you make a passive thermostat out of it? Suck air
only when the sun shines?
The sinking, specifically.
Jeroen
One might guess that the sinking would be exactly the same.
I suppose it pretty much would be exactly the same sinking.
But NO! The gravity is less, so it would *have* to sink less, and the
rule includes that the water is standard Earth sea level density water.
[...]
On 2013-02-18 16:29, SoothSayer wrote:
On Mon, 18 Feb 2013 14:50:23 +0100, Jeroen Belleman
On 2013-02-18 14:35, SoothSayer wrote:
On Mon, 18 Feb 2013 23:41:00 +1100, Sylvia Else
So how much net force is there? Well, if the pingpong ball were not
there, then in its place would be a sphere of water. Since the water
wouldn't go anywhere, the net force on that sphere must be equal to its
weight. Thus the force on the pingpong ball is equal to the weight of
the water that would have been there had the ping pong ball not been.
In other words, it only sinks a small bit because that small bit of
volume, in the form of water, would weigh the same as the ping pong ball.
So, if it displaces one teaspoon (for the sake of the analogy), then the
weight of one teaspoon of water and one ping pong ball would balance on a
scale (be the same).
On the Moon, it would sink far less. And the water wouldn't last long
either! (unless you were aboard The Eagle).
You may want to think about that last statement a little longer....
Jeroen Belleman
About the sinking, the water, or the Eagle?
The sinking, specifically.
Jeroen
One might guess that the sinking would be exactly the same.
I suppose it pretty much would be exactly the same sinking.
But NO! The gravity is less, so it would *have* to sink less, and the
rule includes that the water is standard Earth sea level density water.
[...]
Let's stay within the confines of normal atmospheric pressure and
temperature. Just considering the effects of gravity, of course, on
the moon the ball weighs less, but so does the water, and by the
same proportion. The sinking is therefore the same.
An interesting case to think about is what would happen in perfect
weightlessness: What's the final state if a free floating blob of
water touches a free floating ping pong ball?
kerplop.
(Hint: Surface
tension reigns.)
Thanks, guys, for the inputs.
Those are the classical arguments. I accept them as true and useful
models for everyday use.
But, I'm still not satisfied.
Throw a sheet of thin plywood into the swimming pool.
If you put sufficient force on it, it sinks.
Now turn it vertical and push it down.
The force to submerge it should not change.
But the direction of force applied by all the molecules banging
on the side do not obviously have a net upward force.
The thing I'm trying to get my brain around is convection.
If I have a 20 foot chimney and build a fire in the firebox,
air gets sucked in the box and goes up the chimney.
If I cut a hole in the bottom and stack it on top of a
similar chimney (close up the front), does the same amount
of air get sucked into the bottom (cold) fireplace?
My intuition says it does.
And that means that if you're interested in ventilation,
it doesn't matter where the heat gets into the pipe.
Solar collector should work for that. And the distance
to the space to be ventilated should be irrelevant???
OK, so now, put an S-curve in the pipe, kinda like a P-trap.
Can you make a passive thermostat out of it? Suck air
only when the sun shines?
mpm said:Hummm..... depends on how deep.
I'm pretty sure if you submerge an ordinary ping-pong ball
deep
enough, it will never submerge. Pressure would eventually
crush the
ball into a tiny blob of whatever ping-pong balls are made
of -
likely letting the air out in the process. Or, the ball
ruptures and
fills with water.
On Mon, 18 Feb 2013 17:26:18 +0100, Jeroen Belleman
On 2013-02-18 16:29, SoothSayer wrote:
On Mon, 18 Feb 2013 14:50:23 +0100, Jeroen Belleman
On 2013-02-18 14:35, SoothSayer wrote:
On Mon, 18 Feb 2013 23:41:00 +1100, Sylvia Else
So how much net force is there? Well, if the pingpong ball were not
there, then in its place would be a sphere of water. Since the water
wouldn't go anywhere, the net force on that sphere must be equal to its
weight. Thus the force on the pingpong ball is equal to the weight of
the water that would have been there had the ping pong ball not been.
In other words, it only sinks a small bit because that small bit of
volume, in the form of water, would weigh the same as the ping pong ball.
So, if it displaces one teaspoon (for the sake of the analogy), then the
weight of one teaspoon of water and one ping pong ball would balance on a
scale (be the same).
On the Moon, it would sink far less. And the water wouldn't last long
either! (unless you were aboard The Eagle).
You may want to think about that last statement a little longer....
Jeroen Belleman
About the sinking, the water, or the Eagle?
The sinking, specifically.
Jeroen
One might guess that the sinking would be exactly the same.
I suppose it pretty much would be exactly the same sinking.
But NO! The gravity is less, so it would *have* to sink less, and the
rule includes that the water is standard Earth sea level density water.
[...]
Let's stay within the confines of normal atmospheric pressure and
temperature. Just considering the effects of gravity, of course, on
the moon the ball weighs less, but so does the water, and by the
same proportion. The sinking is therefore the same.
Ahh, so on the surface of Jupiter, it would sink completely!
Oh...
An interesting case to think about is what would happen in perfect
weightlessness: What's the final state if a free floating blob of
water touches a free floating ping pong ball?
kerplop.
(Hint: Surface
tension reigns.)
Unless the ping pong ball is coated with RainX.
Pimpom said:It will still float if the material is less dense than
water, which may well be the case although I'm not sure
either way (wish I had a ping-pong ball I could test that
with). Some common plastics *are* less dense than water.
Or even better:
It will still float if the material is less dense than
water, which may well be the case although I'm not sure
either way (wish I had a ping-pong ball I could test that
with). Some common plastics *are* less dense than water.
FAR OUT!!!
I wonder if the Earth were coated with that if we would not have a Moon
right now, 'cause the impactor slid right past...
I know this isn't the right group for this question, but I want
an answer an electrical engineer can understand.
I understand the simple model of buoyancy. If something weighs
less than the medium it displaces, it floats.
The question is, "why?"
If you stick a ping pong ball under water and let go, it floats.
What's the mechanism? The water has no idea what's inside the
ball. We have water molecules banging into the ball on all sides.
Is there a simple explanation, in layman's terms, of what's actually
going on to force the ball up?
I really want to understand how convection works in a chimney,
but water should be easier to grasp.
I was also talking about solid plastics. The range ofUwe said:Hello,
but we are talking about solid plastics, no foamed
plastics with gas
filled bubbles inside. If the density is less than the
density of
water, it will float, if the density is larger, it will
sink.
I'll take your word on that.Ping-pong balls are made of Celluloid which seems to have
a density of
about 1.67. If they are crushed and filled with water,
they will sink.
Ignoring gravity gradient effects, isn't the simple buoyant rule that
a floating object displaces an amount of water equal to the object's
weight?
I was also talking about solid plastics. The range of
plastics with a density less than that of water may not be
very wide - I don't know, I'm no expert on plastics - but
products made from them are quite common.
I'll take your word on that.
Ignoring gravity gradient effects, isn't the simple buoyant rule that
a floating object displaces an amount of water equal to the object's
weight?
Without gravity, there is no "floating".