How fast does rain fall

A.� In still air, where they receive no assistance from the wind, raindrops fall at speeds between 7 and 18 miles per hour.

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Q.� What determines a raindrops speed

A.� Their size: the bigger they are the faster they fall.

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Q.� How big are raindrops

A.� Cloud droplets become raindrops when they reach 1/100 of an inch in diameter, at this size the gravitational pull is sufficient to make them fall as rain. The smaller raindrops, which fall at the slowest speeds, are around 1/50 of an inch in diameter. The largest raindrops, that can fall as fast as 18 miles an hour, can be as big as a quarter of an inch.

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Q.� Why don't they fall any faster than 18 miles an hour

A.� Because at this speed friction with the air breaks the raindrop up to a smaller size so that it's no longer big enough to reach a faster speed.

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Q.� What shape are raindrops

A.� When they're small enough to be held as cloud droplets they're spherical. However once they're big enough to form raindrops they're not the tear shapes most people assume they are.

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Because the raindrops are falling through air, and therefore coming up against some resistance, they have flattened bottoms and a domed top.

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Q.� How does drizzle differ from rain

A.� Drizzle drops are usually less than 1/50 of an inch in diameter. Drizzle usually seems to be mixed up with the wind, rather than forming distinct separate drops, and it usually falls from low clouds or fog.

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Another distinction is how meteorologists quantify the two. Drizzle is measured in terms of how much it reduces visibility whereas rain is measured in how much accumulates over a period of time.

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Q.� Is it better to run or walk home in the rain

A.� The experts are divided on this one but to the layman it doesn't appear that it makes any difference. If you run, then although you get inside quicker, you hit more raindrops than if you walked. However walking home will take longer than running and so you'll be exposed to a greater amount of rain.

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Do you have a question about the weather

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by Lisa Cardy