# Physics Photo of the Week

## May 4, 2012

Coriolis Effect - An experiment done by the students in Earth, Light, and Sky (PHY-121)

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 rate.   Two 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 left photo.

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 for example).

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 dcollins@warren-wilson.edu.

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.

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