fr:Poids apparent

The apparent weight of an object is the value a spring weighing scale would measure. It is the reaction force by the floor that prevents the object from falling through it, keeping the acceleration of the object and the floor the same. The apparent weight is the total downward force minus that corresponding to the downward acceleration of the floor and the object.

Thus it deviates from the weight if there is another force than gravity and the reaction force, or if the object and the scale experience any vertical acceleration, e.g.:

• in space
• in a lift or rocket
• when some other force than gravity and the reaction force acts on the object, e.g.:
  • a magnetic force
  • buoyancy, if the object is immersed in a fluid

Weightlessness means that the apparent weight is zero.

External references

• Physical demonstration with applet (http://physics.bu.edu/~duffy/semester1/c21_apparent.html)
• Nasa definition (http://microgravity.msfc.nasa.gov/education/WhatisMicrogravity/DefiWeight.htm)
• Exploratorium explanation  (http://www.exploratorium.edu/ronh/weight/index.html)
• Elevator problem (http://hyperphysics.phy-astr.gsu.edu/hbase/elev.html)