Physics Photo of the Week
September
26, 2008
Beaded water and pollen
After
a brief rain shower in mid May and a recently re-stained deck, the
rainwater beaded up (see PPOW
for September 1, 2006). However, mid May is
the
time for white pine to produce prodigious amounts of pollen - it
collects on all horizontal surfaces. When the pollen-strewn deck
was
moistened with the rainwater, the pollen grains tend to coalesce and
float to the tops of each beaded water droplet. These collections
of
pollen show up as the light specks in the center of each droplet.
On
the left end of the photograph the water drops have evaporated and left
the coalesced pollen piles in a random array. You can
notice
the same effect on practically any horizontal surface that has a layer
of uniformly distributed dust, which has been sprinkled with rain -
especially cars soon after washing!
The physics of the effect of
coalescing is quite complicated. If you
sprinkle pepper on your soup, the flakes of pepper are seen to attract
each other. This is a combination of surface tension of the
water and
self-adhesive forces in the dust, pollen, or pepper.
| To show that these specks are
actually pollen, I made two close-up photos of the patches, which are
reproduced here on the right. The left picture is one of the
patches of
pollen floating on top of a water droplet. The bottom image is a
patch
of dry pollen grains after a water drop evaporated. Note the
interesting convolution and "folds" in the floating pollen patch.
The
physics of this effect is a complete mystery to me. |
|
|
These close-up photos
were taken by the
simple technique of holding a powerful magnifier up to the lens while
the camera "looks" through the lens. This is similar to using a
magnifying lens in front of your eye.
Physics
Photo of the
Week is
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature an interesting phenomena in
the world around us. Students, faculty, and others are invited to
submit digital (or film) photographs for publication and
explanation. Atmospheric phenomena are especially welcome.
Please send any photos to dcollins@warren-wilson.edu.
Click
here to see the Physics Photo
of
the Week Archive.
Observers are invited to submit
digital photos to:
