* Buoyancy: Air, like any fluid, exerts an upward buoyant force on objects immersed in it. This force counteracts the object's weight, making it feel lighter.

* Vacuum: In a vacuum, there is no air, and therefore no buoyant force.

Therefore, the object will experience a greater gravitational force and appear heavier in a vacuum than in air.

However, the actual mass of the object remains the same. Mass is a fundamental property of matter and does not change with its surroundings. Only the *apparent mass* (the perceived weight) changes due to the effects of buoyancy.