Keel
That would be its keel.
center board
sideways
up
no
answer down not sideways apex confirmed
friction
Because it's a boat...it slides haha
Friction. Or drag. Kind of the same thing, but drag is mostly used through air or water, which is what you asked.
Retaining walls are at least partially below gound or water level. Their function is to retain the soil or water behind them.This means that a large part of the load they bear is sideways and that they must resist overturning, sliding and bowing as well as any vertical loads.
Because water helps us digest foods, and keeps our bodies running
It refracts four times.