The sun rises over the horizon, reference frame is horizon.
A bus moves past people standing on the sidewalk, reference frame is people on the sidewalk.
A passenger on that same bus sees a ball roll down the aisle, reference frame is the train aisle.
Two trains traveling at the same speed on parallel tracks race past passengers who are waiting on a local station's platform, reference frame is the station's platform.
A passenger on one of those trains looks out the window and sees the other train standing still, reference frame is the other train standing still.
A person standing near a railroad track sees a train pass by, then notices an airplane fly overhead in the same direction as the train, but at a much faster speed, reference frame is railroad track.
A passenger in that airplane looks down and sees the train moving backward, reference frame is insideof the airplane.
A passenger in that airplane looks across the aisle and sees a child tossing a ball up and down, reference frame is the aisle.
What is reference frame?
Reference frame can be described as the stationary background to which an object is compared to tell if it is moving.
A frame of reference is therefore a purely kinematical device, for the geometrical description of motion without regard to the masses or forces causing the motion.
The instance we discussed had different reference frames all of which are the stationary background of the objects.
In conclusion, reference frame of an object describes the motion without regard to the forces causing the motion.
