On Monday, January 14, 2019 at 10:26:30 AM UTC+2, Tom Roberts wrote:   
   > On 1/13/19 4:23 PM, Luigi Fortunati wrote:   
   > > Circular motion without centripetal force is impossible. And then we   
   > > must find a plausible explanation for this case. There is a rotating   
   > > table and a disc without friction. If a person in the laboratory   
   > > gently lays the disk on the rotating table and if the friction is   
   > > (really) 100% absent, the disk, in the absence of friction, can not   
   > > be dragged from the table, so it remains still while the table turns   
   > > downstairs without disturbing.   
   >   
   > Note the disk remains "still" relative to the inertial frame in which   
   > the center of the rotating table is at rest.In discussions like this you   
   > must always mention which frame or coordiantes you are using.   
   >   
   > > For the observer who rotates with the table, the disk travels around   
   > > a circle without ever moving away or nearing the center of rotation.   
   > >   
   > > How can we justify the rotary motion in the accelerated reference if   
   > > no centripetal force acts on the disc?   
   >   
   > In the rotating frame there must be a centripetal force: the disk is   
   > not "fleeing away from the center", so there must be a centripetal force   
   > to balance the (fictitious) "centrifugal force" in the rotating frame.   
   > Note this centripetal force is every bit as fictitious as the   
   > "centrifugal force" -- both are artifacts of using non-inertial coordinates.   
   ============================   
   artifacts ??!!   
      
   imagine a child standing in a  buss   
   not holding anything to stabilize himself   
   now   
   the buss is making a very sharp turning movement   
      
   and the child is falling  away towards the   
   outside direction of that circular movement   
   **AND IS GETTING HURT** (getting injuries!! )   
      
      
   is that  harmful accident is   
   ''fictitious    ''??   
      
   TIA   
   Y.P   
   ===========================   
      
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