- An experiment done by the students in Earth, Light, and
Watch the path of the frictionless
air puck carefully. Notice that it curves upward in
the picture. The table is horizontal, however, so
there is no real force directed toward the top of the
photo. The table is rotating.
When an object is moving across a rotating platform in
the absence of friction it actually moves in a straight line
with constant speed (Newton's Law of Inertia).
However, relative to the rotating table it appears that the
object veers to one side. This is simply the result
that the table is rotating underneath the object. This
video was made by means of supporting the camera with a
framework of rods and clamps that is attached to the
rotating table - see the picture below right. Students around
the table held on to the table and kept cart/table rotating
counter clockwise with a constant rotation
other students played "catch" with the puck. The
camera fixed to the rotating table does not see the rotation
of the table but records the puck veering to the puck's
right. This is called the Coriolis Effect. The
close-up of the details of the camera clamp is shown in the
To prove that the puck actually travels in a straight line, the camera was later mounted on the fixed ceiling looking down on the rotating table. The result is shown in the picture at right. A trace of the puck's travels clearly shows a straight line relative to the fixed ceiling or floor. In this video clip we can see the students' feet walking the table in a counter clockwise rotation and the student on the end is playing "catch" with a student on the side, but the student on the end aimed at the student on the other end.
The Coriolis effect is a powerful effect on the Earth's
weather patterns. When winds blow from all directions
towards a low pressure center, the Coriolis effect due to
the rotating Earth causes the winds to swirl
counter-clockwise in the northern hemisphere creating
cyclones and hurricanes. Incidentally, the swirling of
water in a bathtub drain or toilet flushing is not the
Coriolis effect. The slowness of the Earth's rotation
(once a day) and the small scale of bathtubs and toilet
bowls generates such a small Coriolis effect that it cannot
be noticed. The swirling currents in ordinary drains
is a result of conservation of angular momentum the water
had from an external factor (angled jets in the toilet bowl
Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature 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 firstname.lastname@example.org.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photoprovider is forbidden.