Lets make it simple and avoid math:
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<br>You create wind in relation to yourself when you move, and it can be felt in your face. The faster you move, the faster the wind in your face.
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<br>If there is also a natural wind blowing, as in a cat, both winds are added, creating what is called "apparent wind"
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<br>As it would be expected, the apparent wind is different in direction and strength from both the natural wind and the created wind.
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<br>The apparent wind blows from a direction between the direction of them both, but closer to the fastest (the greater the difference, the closer to the faster wind direction).
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<br>It has a strength which is slightly less then the sum of both winds, and the closer they blow in dierection, the closer the wind strength is to the summ.
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<br>You can perceive this easily going upwind and downwind in sequence. Upwind the wind "feels" strong and straight downwind it feels weak.
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<br>I hope it helps,
<br><br><br>Luiz