Question: why is the real mass of an object different from the mass measured in air

title: Mass versus weight
text: Objects on the surface of the Earth have weight , although sometimes this weight is difficult to measure . An example is a small object floating in water , which does not appear to have weight since it is buoyed by the water ; but it is found to have its usual weight when it is added to water in a container which is entirely supported by and weighed on a scale . Thus , the `` weightless object '' floating in water actually transfers its weight to the bottom of the container ( where the pressure increases ) . Similarly , a balloon has mass but may appear to have no weight or even negative weight , due to buoyancy in air . However the weight of the balloon and the gas inside it has merely been transferred to a large area of the Earth 's surface , making the weight difficult to measure . The weight of a flying airplane is similarly distributed to the ground , but does not disappear . If the airplane is in level flight , the same weight - force is distributed to the surface of the Earth as when the plane was on the runway , but spread over a larger area . 

Answer: answer: The weight of the balloon and the gas inside it has merely been transferred to a large area of the Earth's surface, making the weight difficult to measure.  If the airplane is in level flight, the same weight - force is distributed to the surface of the Earth as when the plane was on the runway, but spread over a larger area.
answer: A balloon has mass but may appear to have no weight or even negative weight , due to buoyancy in air . However the weight of the balloon and the gas inside it has merely been transferred to a large area of the Earth 's surface , making the weight difficult to measure .