Effects of the Earth’s Rotation
C. Chen
General Physical Oceanography MAR 555
School for Marine Sciences and Technology Umass-Dartmouth 1 One of the most important physical processes controlling the temporal and spatial variations of biological variables (nutrients, phytoplankton, zooplankton, etc) is the oceanic circulation. Since the circulation exists on the earth, it must be affected by the earth’s rotation.
Question: How is the oceanic circulation affected by the earth’s rotation?
Question: What is the Coriolis force? How is it defined? What is the difference between centrifugal and Coriolis forces?
2 Definition:
• The Coriolis force is an apparent force that occurs when the fluid moves on a rotating frame.
• The centrifugal force is an apparent force when an object is on a rotation frame.
Based on these definitions, we learn that • The centrifugal force can occur when an object is at rest on a rotating frame;
•The Coriolis force occurs only when an object is moving relative to the rotating frame.
3 Centrifugal Force
Consider a ball of mass m attached to a string spinning around a circle of radius r at a constant angular velocity ω.
r ω ω
Conditions:
1) The speed of the ball is constant, but its direction is continuously changing; 2) The string acts like a force to pull the ball toward the axis of rotation. 4 Let us assume that the velocity of the ball:
V at t V + !V " V = !V V + !V at t + !t ! V = V!"