[thedoc (OP)]

Aman Sharma  asked the Naked Scientists:
   
Does Archimedes' principle work in absence of gravitational force or space also?

What do you think?

[evan_au]

Archimedes' Principle is expressed in terms of a less-dense object (like a boat) being partially submerged in a denser fluid, causing it to float. The mass of displaced fluid equals the mass of the floating object.

Archimedes' probably could not envisage an environment where both the water and the boat would float in air!

Archimedes' principle is an application of a more general principle that systems seek the lowest energy state (all other things being equal). On the earth's surface, a boat partially sinking into the water is a lower energy state than either a boat floating above the water, or a watertight boat completely submerged in the water.

However, when the water and the boat are both in orbit, there is no energy difference between the boat floating "above" the water, or totally submerged in it (ignoring surface tension). So there is no lower energy state in which Archimedes Principle could work.

To create such an energy difference, you could spin the experiment, and so centrifugal force substitutes for gravity, and Archimedes Principle will work.

[LB7]

Yeah it works without gravity, it is possible to have a like Archimede's principle with springs. Look at the device in the drawing.

[alancalverd]

Archimedes Principle actually has nothing to do with force! Quite simply, our hero discovered that when a body is immersed in an incompressible  fluid, it displaces its own volume of fluid. This is true in zero gravity or 1000g.

Obviously if the displaced volume was originally in equilibrium, the immersed body will experience an upthrust equal to the weight of the displaced fluid. If g = 0, W = 0!

[LB7]

Archimedes Principle actually has nothing to do with force! Quite simply, our hero discovered that when a body is immersed in an incompressible  fluid, it displaces its own volume of fluid. This is true in zero gravity or 1000g.

Obviously if the displaced volume was originally in equilibrium, the immersed body will experience an upthrust equal to the weight of the displaced fluid. If g = 0, W = 0!

You can create an artificial medium composed of spheres, without a mass and attract the spheres with springs. The springs replace the gravity and like that I don't need a mass. One spring for each sphere. In that case, g=0 but there is an artificial force s from the springs and they "simulate" the mass of the meidum so the force (simulate the weight) needed to displace the fluid is not 0.

[evan_au]

Archimedes Principle actually has nothing to do with force! Quite simply, our hero discovered that when a body is immersed in an incompressible  fluid, it displaces its own volume of fluid. This is true in zero gravity or 1000g.

I agree entirely, Alan, when applied to an object entirely submerged in a fluid. This fact would have allowed Archimedes to detect the thief who adulterated the king’s gold crown (or so the story goes).

However, Archimedes principle is also often applied to objects which are partially submerged in a fluid (like a boat). In this case, only part of the object’s volume is displaced, and the mass displaced equals the mass of the floating object. For this to work, you do need some force (like the “force” of gravity).

[LB7]

(like the “force” of gravity).

And it is possible to replace the force of gravity by springs, at least in theory.

[evan_au]

PS: looking into it further, I found that:

"Eureka", reportedly exclaimed by Archimedes upon discovery that the volume of displaced fluid is equal to the volume of the submerged object (note that this idea is not Archimedes' principle)

I also found that Archimedes principle applies to the buoyancy force, and applies to both floating and submerged objects.

See: https://en.m.wikipedia.org/wiki/Archimedes%27_principle#Principle_of_flotation

[alancalverd]

Archimedes' Principle is expressed in terms of a less-dense object (like a boat) being partially submerged in a denser fluid, causing it to float. The mass of displaced fluid equals the mass of the floating object.

Pedant alert!

Archimedes' given problem was to determine the density of a supposedly-gold crown. His discovery was made when he got into a full bathtub. Gold doesn't float, and fit living humans are overall denser than water. The eureka moment was the realisation that the displaced volume always equalled the immersed volume.

The secondary effect is that if the displaced weight equals the weight of the entire object, part of the object will float above the surface.

If g = 0 then W = 0, so you can fully immerse any object in any liquid in the absence of gravity. https://www.nasa.gov/audience/foreducators/5-8/features/F_Carbonated_Beverages_Space.html deals with an extreme case!