In physics, apparent weight is a property of objects that corresponds to how heavy an object is. The apparent weight of an object will differ from the weight of an object whenever the force of gravity acting on the object is not balanced by an equal but opposite normal force. By definition, the weight of an object is equal to the magnitude of the force of gravity acting on it. This means that even a "weightless" astronaut in low Earth orbit has almost the same weight as he would have while standing on the ground.
An object that rests on the ground is subject to a normal force exerted by the ground. The normal force acts only on the boundary of the object that is in contact with the ground. This force is transferred into the body; the force of gravity on every part of the body is balanced by stress forces acting on that part. A "weighless" astronauts feels weightless due to the absence of these stress forces, which ultimately derives from there not acting a normal force on the astronaut.
By defining the apparent weight of an object in terms of normal forces, one can capture this effect of the stress forces. A common definition is "the force the body exerts on whatever it rests on."
The apparent weight can also differ from weight when an object is "partially or completely immersed in a fluid", where there is an "upthrust" from the liquid that is working against the force of gravity. Another example is when an object or person is riding in an elevator. When the elevator begins rising, the object begins experiencing a force in the downward direction. If a scale was used, it would be seen that the weight of the object is becoming heavier because of the downward force, changing the apparent weight.
The role of apparent weight is also important in fluidization, when dealing with a number of particles, as it is the amount of force that the "upward drag force" needs to overcome in order for the particles to rise and for fluidization to occur.
Famous quotes containing the words apparent and/or weight:
“If we ever feel discouraged by the apparent constraints on humanity, about its lack of elbowroom and freedom of action, we should think of the Jews and the Greeks, insignificant, powerless, and tiny in the age of the dinosaur empires, yet providing the growing points for the next stage in human destiny.”
—Barbara Ward (1914–1981)
“Not the less does nature continue to fill the heart of youth with suggestions of his enthusiasm, and there are now men,—if indeed I can speak in the plural number,—more exactly, I will say, I have just been conversing with one man, to whom no weight of adverse experience will make it for a moment appear impossible, that thousands of human beings might exercise towards each other the grandest and simplest of sentiments, as well as a knot of friends, or a pair of lovers.”
—Ralph Waldo Emerson (1803–1882)