The boat had triangular sails.
The boat was small and had two triangular sails.
obtuse angle
That's a reflex angle. 0 to <90 Acute angle 90 Right angle >90 to <180 Obtuse angle 180 Straight angle >180 to <360 Reflex angle 360 called Full circle
just an angle, like any other angle.
A windmill is a building with "sails."
I don't think there is another name other than blade.
windmill
A Dutch building with sails is commonly called a windmill.
becuse of the force
A windmill does not blow.A windmill is blown by the wind.The windmills sails turn the wind into power to operate machines, pumps or electrical generators.
by all the wind that builds up on the windmill
A windmill, like in the Netherlands.
The wind blown in the fantail turns the main sails to point to the wind.
A tower mill is a type of vertical windmill consisting of a brick or stone tower, on which sits a wooden 'cap' or roof, which can rotate to bring the sails into the wind.
By capturing the power of the wind as it passes the windmill's sails. This causes the sails to turn, which rotates the sails axle and this, through gears and cogs, powers the pump or the grind stones.
There may be a small propeller on the opposite side to the main sails or there may be a vane to turn the windmill. See the examples in the links below. There may be a small propeller on the opposite side to the main sails or there may be a vane to turn the windmill. See the examples in the links below.