# The coriolis acceleration

1. Jan 11, 2012

### zezima1

Let aS denote the acceleration of an object as measured in a reference frame S that accelerates relative to another reference frame with an acceleration aI. We then have that the absolute acceleration of the object as measured in an inertial frame of reference is given by:
a = aS + aI + aC
where a is the socalled coriolis acceleration, which I have a lot of trouble getting around. Can anyone give me some intuition on why you add this term other than the mathematics behind it. For me you could just as well add the accelerations like you add velocities but then of course, I don't really know if I have a lot of intuition as to how acceleration behaves as seen from different frames of reference.

2. Jan 11, 2012

### Ken G

I think the problem is that there is a big difference between a reference frame that is "accelerating", which suggests a spatially fixed acceleration throughout, and one that is "noninertial", which allows the acceleration to vary with location. The classic example of a noninertial frame is a rotating frame, which is a frame in which you will see things like coriolis and centrifugal accelerations. These accelerations are not everywhere the same in either magnitude or direction, so are both to be distinguished from simple translational accelerations of the entire frame. In practice, the only accelerating frames you need to understand are those with a spatially fixed acceleration (if the observer is accelerating) and those that are rotating (if the observer is rotating). That's all an observer can (instantaneously) be doing that would affect Newton's laws.

3. Jan 11, 2012

### zezima1

okay but if the coriolis acceleration is only something which occurs in a rotating frame, why don't the equations of motion account for the fictitous forces that occur in a linearly accelerated frame - e.g. being pushed back in a car etc.

4. Jan 11, 2012

### Ken G

They do, that's the aI in your original expression-- but that kind of force is not called the coriolis force.