Final answer:
The curtain gets drawn out of a window when it's windy due to Bernoulli's principle, which describes how an increase in the speed of fluid (air) leads to a decrease in pressure, causing the higher indoor pressure to push the curtain outward.
Step-by-step explanation:
The phenomenon of a curtain being drawn out of a window when it's windy can be explained by Bernoulli's principle. This principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. As wind passes quickly over the outside surface of the curtain, it creates a lower pressure than the air inside the room. As a result, the higher pressure inside pushes the curtain towards the lower pressure area outside, causing the curtain to be drawn out of the window.