Caption: Playground merry-go-round with children: playful, happy, carefree---little know they of F=ma.

Playground merry-go-rounds have become a bit uncommon since they are considered a bit too dangerous.

Playground merry-go-rounds are non-inertial frames because they are rotating frame which are made up of continuum of non-inertial frame.

In a rotating frame, there can be accelerations NO ORDINARY forces acting.

Throw a ball on a rotating playground merry-go-round and it follows a curved path in the horizontal plane even though there is NO ORDINARY force to bend its path.

From the ground frame which is an inertial frame (to sufficient approximation), the ball's path is straight.

Rotating frames can be converted to inertial frame using the rotating frame inertial forces (see file: Mechanics file: frame_rotating.html). The most familiar of these inertial forces is the centrifugal force which tries to throw you outward and to stop this you have to hang onto the bars. It's great fun.

Credit/Permission: © User:Jayhawksean, 2005 / Creative Commons CC BY-SA 3.0.
Image link: Wikipedia: File:Merry-go-round.jpg.
Local file: local link: merry_go_round.html.
File: Mechanics file: merry_go_round.html.