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Author Topic:   Buoyancy II

AZdave posted 07-14-2011 06:39 PM ET (US)
It seems that Ole and Lars are returning home in their Whaler. The boat is loaded with rocks destined for Lena's rock garden. On their way home they must pass through a lock. The lock fails during filling and no water can enter or leave. Our boys can't reach the safety ladder to pull themselves out, but Ole has a great idea. He and Lars begin throwing rocks out of the boat into the water so their Whaler will float higher, and they can escape. The question is: Will the water level on the wall of the lock go higher, lower, or stay the same as the rocks are thrown overboard?
Chuck Tribolet posted 07-14-2011 07:19 PM ET (US)
Assuming the rocks don't float (there's a pumice that does
float) the water level will go down. The whaler is displacing
a volume of water whose weight is the same as the rock. Since
the water is less dense than the rock, the volume of displaced
water is greater than the volume of the rock.
If the rocks float, the water level will stay the same.
Chuck
jimh posted 07-14-2011 11:08 PM ET (US)
That is certainly a non-intuitive outcome.
jimh posted 07-14-2011 11:12 PM ET (US)
Later, after getting through the lock, this conversation takes place between Ole and Lars:
Lars: Ole, you need to get some new curtains in your bedroom.
Ole: What are you talkin' about der, Lars?
Lars: I's walking by your house last Saturday night. Da light was on in da bedroom window and I could see you and Lena goin' at it through the curtains.
Ole: Hah! Joke's on you, Lars--I wasn't even home last Saturday night!
Binkster posted 07-14-2011 11:34 PM ET (US)
This question cannot be answered, not enough info. We need to know what size Whaler was used and what the displacement of that boat would be, as common sense would tell us that a 10 lb. rock, say, would not make a 27 foot Whaler, sit lower in the water as the same weight rock weight would have on a 13 footer.
Dave Sutton posted 07-15-2011 12:39 AM ET (US)
"This question cannot be answered, not enough info"
Uhhhh.... <sigh>.... yes it can, and Chuck T has the right answer. It makes no difference what size boat it's done out of.

Here's a better one, which I use as a physics example at Test Pilot School:
I bring 10 chickens aboard a 747. We then take off and go flying. I release them in the cabin, and take a bullwhip and start cracking it at them. Doing so, I am able to make them all fly within the cabin at one time. The question is, at the moment they are all in flight, does the wing of the 747 still carry their weight, or does the aircraft carry a load lesser by the weight of the internally-airborne chickens?

Dave Sutton
macfam posted 07-15-2011 07:55 AM ET (US)
The chicken in the airplane expiriment has already been tried.
The moment all the chickens were airborne in the plane, the weight distribution changed dramaticaly. Some chicken became chicken, although technically they were already chicken, and landed, then took off again when they wern't chicken any longer. The other chickens didn't get chicken, and they remained flying.
Due to the erratic weight distribution the plane acted violently, and the pilot became chicken. Once the pilot became chicken he too began to fly in the plane, although techically, he was already flying the plane.
You guessed it....the plane chashed and most data was lost.
The pilot was severly injured but lived. His name was George F. Crouch

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Author	Topic: Buoyancy II
AZdave	posted 07-14-2011 06:39 PM ET (US) It seems that Ole and Lars are returning home in their Whaler. The boat is loaded with rocks destined for Lena's rock garden. On their way home they must pass through a lock. The lock fails during filling and no water can enter or leave. Our boys can't reach the safety ladder to pull themselves out, but Ole has a great idea. He and Lars begin throwing rocks out of the boat into the water so their Whaler will float higher, and they can escape. The question is: Will the water level on the wall of the lock go higher, lower, or stay the same as the rocks are thrown overboard?
Chuck Tribolet	posted 07-14-2011 07:19 PM ET (US) Assuming the rocks don't float (there's a pumice that does float) the water level will go down. The whaler is displacing a volume of water whose weight is the same as the rock. Since the water is less dense than the rock, the volume of displaced water is greater than the volume of the rock. If the rocks float, the water level will stay the same. Chuck
jimh	posted 07-14-2011 11:08 PM ET (US) That is certainly a non-intuitive outcome.
jimh	posted 07-14-2011 11:12 PM ET (US) Later, after getting through the lock, this conversation takes place between Ole and Lars: Lars: Ole, you need to get some new curtains in your bedroom. Ole: What are you talkin' about der, Lars? Lars: I's walking by your house last Saturday night. Da light was on in da bedroom window and I could see you and Lena goin' at it through the curtains. Ole: Hah! Joke's on you, Lars--I wasn't even home last Saturday night!
Binkster	posted 07-14-2011 11:34 PM ET (US) This question cannot be answered, not enough info. We need to know what size Whaler was used and what the displacement of that boat would be, as common sense would tell us that a 10 lb. rock, say, would not make a 27 foot Whaler, sit lower in the water as the same weight rock weight would have on a 13 footer.
Dave Sutton	posted 07-15-2011 12:39 AM ET (US) "This question cannot be answered, not enough info" Uhhhh.... <sigh>.... yes it can, and Chuck T has the right answer. It makes no difference what size boat it's done out of. Here's a better one, which I use as a physics example at Test Pilot School: I bring 10 chickens aboard a 747. We then take off and go flying. I release them in the cabin, and take a bullwhip and start cracking it at them. Doing so, I am able to make them all fly within the cabin at one time. The question is, at the moment they are all in flight, does the wing of the 747 still carry their weight, or does the aircraft carry a load lesser by the weight of the internally-airborne chickens? Dave Sutton
macfam	posted 07-15-2011 07:55 AM ET (US) The chicken in the airplane expiriment has already been tried. The moment all the chickens were airborne in the plane, the weight distribution changed dramaticaly. Some chicken became chicken, although technically they were already chicken, and landed, then took off again when they wern't chicken any longer. The other chickens didn't get chicken, and they remained flying. Due to the erratic weight distribution the plane acted violently, and the pilot became chicken. Once the pilot became chicken he too began to fly in the plane, although techically, he was already flying the plane. You guessed it....the plane chashed and most data was lost. The pilot was severly injured but lived. His name was George F. Crouch