Thinking Physics Question 5

I think the answer would be a, because if it were completely filled then nothing would happen at all, so these bubbles have effectively negative mass. Although the force of gravity would attract water together, towards the center, the bubbles would move apart.

A, move apart

Because less gravity is exerted on the bubbles in the direction of other than the surrounding liquid, they will tend to be attracted away from each other.

B. If you have an infinite volume of water, the system has no center of mass.

Edit: If the mass of water is finite, there exists a center of mass that the water will gravitate towards, which will push the bubbles outwards, radially. Unless the bubbles begin on the same radius, they will be moving away from each other.

two bubbles have more surface area than the two bubbles combined, so due to cohesion of like molecules the spaces would move towards each other

b, if the bubbles are empty space, they therefore have no mass and are not influenced by gravity.

B empty space doesn't get affected by gravity no?

first of all my english sucks xD
well my answer would be C,,,
you are just replacing an empty space by an space full of water, so i think a bubble would deform that space, which is full of water, so due to that deformation the other bubble will be attracted to the first one. So attraction will be the answer ,,,IMO xD.

But the water surrounding the bubble have mass.

we aren't talking about the water, i don't believe
he also specifies that the bubbles are just the empty space when he says "bubbles (empty spaces)"

edit: oh wait, i think i get what you're saying. that the water around the bubble moves towards an area, effectively moving the entire bubble itself. not sure which one micronesia means, we'll just ask him tomorrow.

Assume the pressure/density is constant in the whole space except the two bubbles. I assume newtonian gravity, no general relativity/deformation of spacetime. Because else space itself might collapse.
Now I assume that the bubbles are shielded against the water, ie by a thin glass wall, else they'd simply fill with water.
The gravity field points cleary away from the bubbles, so the water moves outward until the gravity is compensated by a density/pressure gradient with lower pressure in the space between the bubbles. During the beginning this process the water might take the bubbles outward a bit.
In this new situation the bubbles try to move to the lower pressure and since no gravity affects them they will move inward. So my answer is
c) Move towards each other (attract)

We can just think of the bubbles as particles of negative mass (holes, basically). However, since gravity goes as the SQUARE of the mass, the negative sign cancels out, so they still attract. C

I always though that every object attracts each other, even if you put 2 bottles they still attract each other. Thing that keeps them apart is friction (which is much higher than their force to attract each other.