Physics Photo of the Week

Physics Photo of the Week Feb. 18, 2022  Frosty Silk On the morning of Jan 4, 2022 we woke up to a very rare occurrence of rime ice on the trees in our yard.  I believe the temperature was not terribly cold but a few degrees below freezing.  This resembles ordinary frost that forms on surfaces, but believe it is rime ice judging from the long needle-like crystals forming on all the spruce needles as well as along a couple of old spider silks that stretched between small spruce branches.   This phenomenon is rime ice that was formed from supercooled fog that had descended on our yard during the night.  The fog droplets were below freezing temperature but still liquid when they were suspended as fog.  As soon as the droplets contacted an object (spruce needle, spider web, leaf point, or airplane wing) they freeze instantly.  Rime ice is different from "ordinary frost" or "hoar  frost" in that hoar frost forms by direct sublimation of water vapor directly into solid i

Nature's Thermometer - Rhododendron Leaves   Rhododendron leaves are a good temperature indicator, especially when the temperature is between 20 deg F and 32 deg F.  The leaves shrivel up and practically point downwards.  The plants look like they are shriveling up to die! But no, they are merely responding to the significantly below freezing ambient temperature which was about 20 deg F (-7 deg C).  The next day, Jan 8, 2022, the temperature was above freezing.  The second picture shows my dog investigating the warmer rhododendron leaves that have fully "recovered" I do not know why or how the leaves respond to temperature like this.  Since it is a physical phenomenon about the temperature that water freezes, it is perhaps a mechanism in which the water in the leaves' cells freezes and the cell walls can stretch to accommodate the the larger volume of the water.  Some plants are destroyed by freezing temperatures - presumably because the expansion of the freezing wate