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Relative velocity refers to how quickly and in which direction an object is travelling in relation to another item or a point in space.

In a rainstorm with a high wind, the ideal way to hold a sturdy umbrella is against the direction of the vector sum consequent of the raindrops' velocity plus the wind's velocity. Let's pretend the wind is blowing west and the raindrops are falling vertically downward. The sum of these two vectors is a vector pointing westward from the vertical line, as shown in the diagram below.

Thus, the umbrella must be hold at the same angle as the resulting vector, but in the opposite direction. The vector sum has a westward angle from the vertical line so hold the umbrella at the same angle as before, but facing east toward the vertical line.