14 DAY TRIAL // Fictitious forces, or pseudo forces are, as their name suggests, apparent forces that exert their influence on every object that has a mass in a rotating reference system. The fact that we are living in such a system, the Earth, means that we are influenced by these forces every day.
The first weird thing about these forces is the fact that they are not generated by any physical interaction, but from the acceleration of the system itself. The acceleration forces you feel in a moving car, pushing you back into the seat, the centrifugal force that pushes you against the window on the outside of a curve, these are fictitious forces.
The Earth being a rotating reference system means that such forces must be introduced in order to perform calculations and although they are felt by people on the surface, they can't be perceived by an astronaut, for instance.
Probably the most important fictitious force is the Coriolis force, the apparent deflection of objects from a straight path if the objects are viewed from a rotating system of reference. For instance, winds in the northern hemisphere are deflected to the right of their reflection of travel, exactly because of this force and to the left in the southern hemisphere.
The best way to observe this invisible force in action is to see a fluid in a container rotating on a turntable. Contrary to general expectations, when the container is rotating, the surface of the fluid will take a parabolic shape.
Since Earth is a turntable in a manner of speaking, we are all subjected to these apparent forces, although we may not notice it. Einstein's theory of general relativity was the first to make a clear distinction between real and fictitious forces and he even stated that gravity is also indistinguishable from a fictitious force, which is proven almost 90 years later by many practical confirmations.