Onigashima
Here's a physics puzzle, plurk
Onigashima
Suppose you have a river that crosses a road
Onigashima
but rather than the road being on a bridge over the river
Onigashima
the river goes on an aqueduct over the road
Onigashima
then, a boat on the river goes across the aqueduct
Villain
So the water goes uphill?
Onigashima
does the overall force pressing down on the aqueduct increase?
Onigashima
no
Onigashima
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?
Onigashima
Onigashima
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
Onigashima
the actual answer is much weirder
Rama
Resulting in, mainly, sonewhat compressed water
Onigashima
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
Onigashima
the actual result, as I understand it, is
Onigashima
the displacement caused by the boat effectively spreads the boat's mass across the entire system
Onigashima
meaning that the boat does increase the pressure a miniscule amount, but
Onigashima
from when it enters the river, not from when it reaches the aqueduct
RobotApocalypse
yeah that makes sense to me
Onigashima
the pressure would be multiplied by, approximately,
Rama
Right yeah. The weight is distributed across the whole thing because the water can move outward
Onigashima
(mass of water in river + mass of boat) / (mass of water in river)
Onigashima
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.'