## Earth Sciences and Ecology Question #391

Sandra Diaz, a 13 year old female from the Internet asks on June 8, 1998,

What wind speed would be enough to blow somebody away?

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### John Digby Reid answered on June 8, 1998

Walking against a strong wind can be tough. You lean into it and it's still difficult to make progress. If the wind gets too strong it can blow you away - in a tornado for example.

As the wind speed becomes greater the force of the wind on you is greater, approximately according to the square of the wind speed - twice as strong a wind means four times the force on you. You can reduce the force by turning sideways to it, and by leaning forward to reduce the area you present to the wind.

Therefore I can't give a definite speed at which you would be blown away. Generally speaking, a person starts to have to lean into the wind when it blows at 25 km per hour. At 60 to 80 km per hour most people will avoid being out in the wind and by 100 km per hour (called a storm force wind) people get blown away. Hurricanes have winds in excess of about 120 km per hour, and in a tornado winds can exceed 250 km per hour.

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