Drag due to any fluid varies with the cube of velocity, meaning that it grows rapidly with increasing speed. This is why a car may need only 25 horsepower in order to cruise at highway speeds, while requiring perhaps 200 horsepower, eight times as much, to travel twice that fast. The effect is even more pronounced in aircraft, where efforts to streamline become vitally important because the power of the engines cannot make up for the increase nearly as easily.