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