Wind movements are also modified in cities because buildings increase the friction on air flowing around them.
风向在城市里也会改变，因为建筑物增加了它们周围流动的空气的摩擦力。
2
The flick of a finger is enough to make a balloon accelerate away. When moving, it has little momentum and even the friction of the air quickly slows it up.
一根手指的弹击足够使一个气球加速离去，当气球运动时，一点动力，甚至空气的摩擦力可以很快使它慢下来。
3
That never changes if there is no air drag or airfriction of any kind.