I keep a motorcycle outdoors under a waterproof cover, but noticed that with morning dew the bike is still noticeablely wet on the inside of the cover.
Meanwhile a buddy has his bike in a plywood shed that is by no means air tight but has 4 walls and a roof, but no insulation or air handling fans/AC and he says dew is never an issue..what’s the difference?
In: Planetary Science
Dew is not rain, and it doesn’t ‘fall’ from the sky. It’s condensation of water vapor that’s in the air.
For your bike, there’s air (that contains water vapor) underneath your cover when you put it on. At night, the temperature of that air drops, and the air can no longer hold as much moisture. The water vapor then condenses onto your bike. I’d bet that you also get dew on the outside of the cover, since the same thing is happening to the ambient air (that’s why dew appears on grass and other surfaces at night).
For your buddy’s bike, the air temperature inside the shed is simply not changing enough for moisture to condensate. Even though it’s not ‘airtight’ or insulated, a relatively closed space makes a huge difference in restricting air movement and slowing down how quickly the air temperature inside changes. In extreme cases (for example, a very hot and humid day followed by a very cold night), I actually would expect some condensation inside the shed, but it’s probably rare.
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