Quinn Angstrom
Here's a physics puzzle, plurk
Quinn Angstrom
Suppose you have a river that crosses a road
Quinn Angstrom
but rather than the road being on a bridge over the river
Quinn Angstrom
the river goes on an aqueduct over the road
Quinn Angstrom
then, a boat on the river goes across the aqueduct
Master Chieve
So the water goes uphill?
Quinn Angstrom
does the overall force pressing down on the aqueduct increase?
Quinn Angstrom
no
Quinn Angstrom
lemme draw it
Dirk Warhard
It doesn't, because the force of gravity on the boat is counteracted by the water pushing up on the boat, right?
Quinn Angstrom
Quinn Angstrom
but then wouldn't the water pushing up on the boat in turn push down onto the aqueduct?
Rama
Yeah the boat presses down on the water which presses down on the aqueduct
Quinn Angstrom
the actual answer is much weirder
Rama
Resulting in, mainly, sonewhat compressed water
Quinn Angstrom
water doesn't actually compress like that, because it's a fluid, so it can move out of the way rather than compress
RobotApocalypse
but the boat also displaces water so there's less water pushing down on the aqueduct at the same time
Quinn Angstrom
the actual result, as I understand it, is
Quinn Angstrom
the displacement caused by the boat effectively spreads the boat's mass across the entire system
Quinn Angstrom
meaning that the boat does increase the pressure a miniscule amount, but
Quinn Angstrom
from when it enters the river, not from when it reaches the aqueduct
RobotApocalypse
yeah that makes sense to me
Quinn Angstrom
the pressure would be multiplied by, approximately,
Rama
Right yeah. The weight is distributed across the whole thing because the water can move outward
Quinn Angstrom
(mass of water in river + mass of boat) / (mass of water in river)
Quinn Angstrom
which, in any realistic scenario, is functionally 1
RobotApocalypse
yeah
RobotApocalypse
so the answer would be "yes but negligibly"
Vehrec
and the practical engineering answer is 'boat displaces it's own weight in water, net effect on the system is zero.'