Fictitious forces are apparent forces that appear to act on objects in non-inertial reference frames. There are four types of fictitious forces:
- Rectilinear acceleration: The apparent force you feel pulling you into the back of your seat when your car accelerates;
- Centrifugal force: The apparent force you feel pulling you to the side of your car when the car turns;
- Coriolis force: The apparent force that causes an airplane headed directly due north to veer West relative to the Earth, because the Earth is rotating beneath the plane.
- Euler force: The apparent force you feel when you are on a merry-go-round and somebody starts to spin the merry-go-round.
Fictitious forces do not have a physical cause—they are artifacts of the observer's being in an accelerated frame of reference. Inertial reference frames are frames of reference which have no fictitious forces.