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Discussion Starter #1 (Edited)
A : If I stand on the end of my boat and pee into Loch Ness, does the water in the loch go up, go down, or stay the same?

B : If I take a floating object from below, and throw it overboard, does the water in the loch go up, go down, or stay the same?

C : If I take a naturally-sinking object from below, and throw it overboard, does the water in the loch go up, go down, or stay the same?

D : If I had Loch Ness on the moon, would my boat float higher, lower, or stay the same?

E : If I heated the water in Loch Ness, and drained off the excess that spilled over the loch level control, would my boat be floating higher, or lower at the water line?

F : If I heated the boat only, would my boat be floating higher, or lower at the water line?

This is Loch Ness....

Loch Ness Map

....there ar 7.5 billion tons of water in this great loch.
 

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A/B/C—stay the same.... but again, the boat will rise a tiny bit... since it now displaces less water.

D—stay the same, since gravity has changed for everything... at least until the water boiled off due to being in vacuum... :)

E—Lower—warm water is less dense than cold water... but you'd really piss off Nessie... :)

F—It depends... some materials contract when heated—they would float lower...since the boat is contracting, it has to sink to displace the same mass of water; others expand when heated—they would float higher... since they're expanding and displacing more water.. :)
 

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Good job SD.
 

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:D thanks badsanta. :)

Now to complicate things... say you have a crew member bring two cases of beer aboard the boat from the local package/liquor store...

What happens to the boat—does it sink or rise?
What happens to the Loch—does it rise, fall or stay the same?
 

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Answer for C is not that simple. When you throw a sinking object overboard, unless it is perfectly rigid it will contract with increasing water pressure as it sinks, and therefore displace less water, so the Loch's level with drop.
 

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:D thanks badsanta. :)

Now to complicate things... say you have a crew member bring two cases of beer aboard the boat from the local package/liquor store...

What happens to the boat—does it sink or rise?
What happens to the Loch—does it rise, fall or stay the same?
Also, what happens when the beer is drunk and the dissolved gasses are belched out? Does the boat sink or rise?
 

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What if the monster eats you?
Will the Loch change color?
 

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Stays the same till you pee overboard!!
 

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After re-thinking it, Adam's right, but it also depends on the density of the object... if the object is really dense, like a solid cube of osmium, the loch's water level will actually go down—since the boat is now displacing less water—equivalent to the mass of the object, but the water level has only rising by the volume of the object itself. The higher the density of the object, the more the loch's level will drop. :)

Answer for C is not that simple. When you throw a sinking object overboard, unless it is perfectly rigid it will contract with increasing water pressure as it sinks, and therefore displace less water, so the Loch's level with drop.
 

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Moon re mass from earth

If we send too much mass to the moon, earth will become lighter and go out of orbit. So we have to be careful because 8.3 lbs per gallon times volume of Loch Ness could spend trouble. Esp when the toad lickers find out...;) [lets not forget to be at least 3 miles out too if we want to pee]
 

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A : If I stand on the end of my boat and pee into Loch Ness, does the water in the loch go up, go down, or stay the same?
Same. You're adding water to the loch, but you're displacing less. (Assumed: Density of your pee equals density of the water in the loch.)

B : If I take a floating object from below, and throw it overboard, does the water in the loch go up, go down, or stay the same?
Same. Total displacement doesn't change.

C : If I take a naturally-sinking object from below, and throw it overboard, does the water in the loch go up, go down, or stay the same?
It goes down. The object you throw over goes from displacing its weight of water to displacing its volume of water. If it sinks, then the latter amount of water is smaller. So less water is being displaced, so the water level goes down. It makes no difference, btw, where the object was on the boat.

(I cheated, btw. That answer was from a friend who is much smarter than I. I originally thought "same," tho I was unsure.)

D : If I had Loch Ness on the moon, would my boat float higher, lower, or stay the same?
Same. Weight changes for everything.

E : If I heated the water in Loch Ness, and drained off the excess that spilled over the loch level control, would my boat be floating higher, or lower at the water line?
Lower. Warm water is less dense than cold. (It helps that I just read the Plimsoll Mark thread ;).)

F : If I heated the boat only, would my boat be floating higher, or lower at the water line?
Hard to say. Higher, I should think, mainly due to material expansion.

That was fun :)

Jim
 

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Joe-

If you were to try and move Loch Ness, I'm sure you'd have a problem with Nessie far earlier than any bureaucrats... Also, the 3 mile limit does not apply if you are discharging directly overboard... only if you use the head or other marine sanitary equipment does the three-mile rule apply. However, Loch Ness is freshwater and as such discharging marine sanitary equipment into it is probably forbidden...but peeing over the rail is probably not. :)

If we send too much mass to the moon, earth will become lighter and go out of orbit. So we have to be careful because 8.3 lbs per gallon times volume of Loch Ness could spend trouble. Esp when the toad lickers find out...;) [lets not forget to be at least 3 miles out too if we want to pee]
 

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If you have a thousand pounds of birds being flown in an airplane and the birds suddenly take flight in that airplane . . . does the airplane then weigh less?
 

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Don't know... if you have a sensitive scale and a pet bird in a cage, you could find out... :)
 

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"If I take a floating object from below,"

If the object is floating below, you're in trouble - the boat's sinking. ;)
 

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Discussion Starter #16
SemJim :
Right on all counts.
Well done.

Johnrb :
Stop being a clever dickie. You are being very silly. Strictly speaking, you could argue that the floating body was floating in the bilge water, and then you threw it overboard. When it's still in the air, the loch level would go down a wee bit, then go up the same (opposite) wee bit when the bilge object that was floating hit the water of the loch. Stop being silly though.
 

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Could be from floating in the head...:puke
"If I take a floating object from below,"

If the object is floating below, you're in trouble - the boat's sinking. ;)
 

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???????????????

I believe it was Archimedes who proved different materials have different specific gravities thence 50 pounds of lead has less volume than 50 pounds of aluminum. So a solid block of lead would displace a smaller volume of water than a solid block of aluminum. So a hull form depends on shape and weight, to determine how much water is displaced. So what is displacement, the actual volume of water that is moved aside when the boat is placed in water or the amount it weighs on the travel lift?
 

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Discussion Starter #19 (Edited)
Rx :

They are exactly the same for a floating body. The ship will displace its own weight of water exactly. It's one of the gems of hydrostatics. We can even prove it mathematically too, though it's not easy for complex geometries. It applies to any floating body, irrespective of its geometry.

If the body naturally sinks, (or your ship floods such that it wishes to sink) it fails to displace its own weight of fluid, and so the seabed, or the bed of Loch Ness, has to support the force shortfall (the difference between the weight of the ship and the water weight it can displace). The vessel is sunk by then though.

All this from Archimedes, from about 250 BC.
 

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"All this from Archimedes, from about 250 BC." - Rockter, he had no computer, so he
a) had a lot of time
b) still knew how to use his head (no google at that time)

By the way a very funny thread.
 
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