Final answer:
The instrument that measures both wind speed and direction is an anemometer combined with a weather vane, which are critical for determining the total velocity of an aircraft.
Step-by-step explanation:
The device that combines to measure wind speed and direction is known as an anemometer combined with a weather vane. The anemometer measures wind speed by counting the number of rotations of its cups or blades, which are propelled by the wind. The weather vane, on the other hand, indicates the wind direction by aligning its arrow with the wind flow, similar to how a "One Way" street sign has a large surface area perpendicular to its pointing direction, causing it to rotate freely in a horizontal plane.
In the case of an airplane, these measurements are crucial because the wind's speed and direction can significantly alter the total velocity and heading of the aircraft. By breaking down the wind velocity into components using vectors, pilots and meteorologists can determine both the magnitude and direction of the wind vector to make informed decisions.