Do masses maintain constant shape and what makes them stay in a form?
407008
Only non-fluids will keep their shape.  If the energy of the constituent particles is not sufficent to overcome the bonding then the mass will keep its shape unless a large force is applied to it.  If the gravitational force is large enough it will most certainly brake objects; would you like to try walking past a black hole?
1123910
Only "large" celestial objects are round. Small ones, like asteroids, can be any shape.\n\nIt is the high gravity of large objects that makes them round. As they accumulated from smaller pieces, any piece that was out of round was pulled by gravity "downhill" so the overall shape of the body is round.
228461
Large bodies of matter, like planets, have a strong gravitational field.  The gravity, created by the mass of the object tends to pull the surface into a shape with the least amount of entropy.  This shape is a sphere.
443935
like charges attract and unlike repel becoz they have electrostatic forces acting.\nbut gravitationis not a force but a property of matter, so like masses attract rather than repel naturally
34520
Gravity shapes objects.  If an objects mass is over a certain threshold then gravity will be strong enough to overcome molecular forces to "mold" an object.  Most asteriods have masses that are too low for this however planets and most moons are massive enough.  \n\nWhy a sphere?  This is due to the inverse radial dependance of the gravitational force.  In order words at a given distance from the center of mass distribution the force of gravity is the same.  This type of shape is a sphere.
1164830
Oh Boy! got it right. The larger asteroids are also basically spherical. This is ultimately due to the fact that they have enough mass for the gravity to force them into this shape. Of course, there are irregularities, but they are fairly small except for the bulges caused by rotation. The smaller asteroids don't have enough mass for the gravity to have much effect.
209689
mass in motion stays in motion unless disrupted by another force!
351894
The law of conservation of mass/matter (The Lomonosov-Lavoisier law) states that the mass of a system of substances will remain constant, regardless of the processes acting inside the system. An equivalent statement is that matter changes form, but cannot be created or destroyed. This implies that for any chemical process in a closed system, the mass of the reactants must equal the mass of the products.\n\nThe two posters above me are wrong. Just because we build and use resources, doesn't mean the weight goes away, it just changes form. People gaining weight, gain it from the earth, it doesn't magically appear.\n\nThe only way the earth would lose mass is, stuff leaving planet earth such as rockets, satalites, ect..\n\nThe only way earth would gain is the space stuff that hits earth every second, and adds to the total weight.
442513
The gravitational force holds it into a spherical shape.
202397
Presumably the mooon is approximately spherical for the same reason that the earth or other round celestial bodies are approximately spherical. Some comments: \n\n1. For solid bodies like the moon and the earth:\n\nThey probably formed as molten, self gravitating bodies, and the sphere is the minimum energy shape. If they rotate, hydrodynamic forces flatten them slightly, making the semimajor axis aligned with the axis of rotation shorter than the other two axes in general. \n\n2. For stars:\n\nAgain, the minimum energy configuration for many standard isolated stars is roughly spherical. If they are rotating, they might be oblate spheroids, but still close to spherical, as long as there are no other very massive bodies close to distort their shape. \n\n3. For nonspherical bodies like asteroids and comets:\n\nThese irregular chunks might have formed after some large body cooled, or not had sufficient mass for gravitational forces to constrain the shape to be spherical. \n\n4. For nonspherical stars:\n\nThere are many stars that are binaries, and the two stars are so close that their shapes are distorted (i.e., their Roche lobes are filled so they look like egg shapes, or they have accreation disks, etc). There might be other processes active that distort them away from spherical shapes. Even large close planets might distort their shapes in some cases.
70579
Interesting. I vaguely remember a "great attractor" from chaos theory, but what I find when I look it up now is that it refers to a cluster of galaxies, "in the direction of Centaurus and Hydra" where nobody is sure why they're grouped like that.\n\nHere's a direct quote from another source though which I think directly addresses what you're asking about: The galaxy rotational problem refers to the phenomenon of the descrepency between the observed rotational motion of the matter of the galactic disc from the predictions of Newtonian dynamics. (See links below and search for "12.25.I".)\n\nI think in layman's terms what they're boggling about is the "bar" shape that occurs in most galaxies, our own apparently included. A recent issue of Scientific American had a very good theory on how that occurs and why.\n\nIf I'm getting the gist of it right, they're not sure why clusters of stars occur in a semi-pinwheel pattern, since based on observed mass there simply isn't enough to cause such a structure to form or remain stable.  The theory in SciAm had something to do with a coincidence of travelling wave patterns rather than any deep dark mysteries of physics, filiments, or anything else.\n\nSee http://www.sciam.com/, October 2005 issue, p. 43, "Ripples in a Galactic Pond." Very nice article and they explained it more clearly than anything I could put together.
173520
all of the matter here already exists, what form it takes doesn't change the total mass.
43539
Planets seem to be spheres, not cubes or cylinders or oddball rocky shapes.  Some smaller bodies such as asteroids or Mars moons Phobos and Deimos, do have odd shapes, but larger bodies like the nine planets and most of their moons do look like spheres.  That's because of the nature of gravity.  You can think of gravity as a force that points inward toward the center of the planet so that every part of the surface is pulled evenly toward the center, resulting in a spherical shape. \nOf course, planets are not perfect spheres because mountains and valleys and even skyscrapers are all deviations from the spherical shape.  However, as planets get larger, gravity gets stronger, until eventually large objects on the surface are crushed under their own weight.  That's why we don't have mountains that are 50 miles high or skyscrapers that are 2,000 stories tall.  Planets stay basically spherical because any large deviations get crushed. \n\nAlthough gravity keeps planets close to spherical, there are other forces that cause deviations from the basic spherical shape.  For example, the rotation of the earth once every 24 hours, causes an apparent centrifugal force which creates a bulge at the equator.  In fact the earth's diameter at the equator is 7,926 miles while the diameter between the poles is only 7,900.
1047922
It all depends on buoyancy and density. \n\nIf the weight of an object is less than the weight of the fluid the object would displace if it was fully submerged, then the object is less dense than the fluid and it floats at a level so it displaces the same weight of fluid as the weight of the object.\n\nIf the object has exactly the same density as the liquid, then it will stay still, neither sinking nor floating upwards, just as the liquid nearby stays still.\n\nUNLESS, \n\nAn object made of a material of higher density than the fluid, for example a metal object in water, can still float if it has a suitable shape (ex: hollow) that keeps a large enough volume of air below the surface level of the fluid. In that case, for the average density mentioned above, the air is included also, which may reduce this density to less than that of the fluid.
78675
The poster before me gave an excellent answer which is that nobody really knows. I just wanted to point you to a very cool experiment about how mass warps space.\n\nAnother very profound question to ask would be why are gravitational mass and inetial mass so nearly (if not exactly) equal?
474542
Gravity does not change the mass of an object, only its weight.\n\nIf you travel away from the Earth, or any concentration of gravity, you will weigh less, but your mass is unchanged.
940178
remains constant   coz u have inertia of motion