[Guest]

Find out the time it takes for two bodies of mass M1 and M2 separated by distance D in space to Collide.? Don't forget to note that gravitational forces becomes stronger and stronger as the bodies approach closer and closer.

F=G.M1.M2/D^2

a=F/m

(HighSchool Physics equations

[Guest]

Gravity's force is inverse square law of the separation of the centers of mass.

But objects don't collide when their centers of mass coincide, they collide when their external surfaces come into contact.

For the problem to be well posed, we need something like:

The centers of two spheres, of mass m₁ and m₂ and radius r₁ and r₂, initially at rest, are separated by a distance d.

Under the force of their gravitational attraction, at what time will they collide?

The answer then is not when d becomes zero but when it becomes r₁ + r₂.

[Guest]

t_f = ((D⁴- (r₁+r₂)⁴)/(6G(m₁+m₂))^1/2

[Guest]

Unless I'm incorrect there is no gravity in space. Am I right?

no there isn't any gravity in space. Why do you think that people float in space? Because they're wearing floating space-suits?

[Guest]

no there isn't any gravity in space. Why do you think that people float in space? Because they're wearing floating space-suits?

For the last time, there is gravity in space. The reason you "float" in space is because the FORCE of gravity is directly dependant on the distance between the two objects in question. When you are in space, you are a lot further from the Earth than when you are on the ground. Weight yourself on a good scale at the beach, then weigh yourself on top of a *really* tall building, you will weigh less on the really tall building because there is more distance between you and the Earth.

In space, you don't really float, its more like you fall *really really* slowly toward the earth, too slow to notice however. The only reasons that satilites don't "fall"toward Earth is because of some fun facts. In reality, they are falling toward Earth, but because the Earth is curved, they just happen to fall towards Earth at the same rate that the Earth is curving away from them -- this causes them to stay in orbit.

[Guest]

For the last time, there is gravity in space. The reason you "float" in space is because the FORCE of gravity is directly dependant on the distance between the two objects in question. When you are in space, you are a lot further from the Earth than when you are on the ground. Weight yourself on a good scale at the beach, then weigh yourself on top of a *really* tall building, you will weigh less on the really tall building because there is more distance between you and the Earth.

In space, you don't really float, its more like you fall *really really* slowly toward the earth, too slow to notice however. The only reasons that satilites don't "fall"toward Earth is because of some fun facts. In reality, they are falling toward Earth, but because the Earth is curved, they just happen to fall towards Earth at the same rate that the Earth is curving away from them -- this causes them to stay in orbit.

Apart from the Apollo missions, nobody's been beyond a low Earth orbit. In LEO, you aren't much farther from the center of the earth than when you are standing at the surface. Certainly nowhere near enough for you to notice a significant difference in Earth's gravity. When you see astronauts floating about in the space station or on a space walk, they are falling (very nearly) as fast as if they had jumped off the Empire State building. However, to misappropriate Douglas Adams, they just keep missing the ground.

[Guest]

Apart from the Apollo missions, nobody's been beyond a low Earth orbit. In LEO, you aren't much farther from the center of the earth than when you are standing at the surface. Certainly nowhere near enough for you to notice a significant difference in Earth's gravity. When you see astronauts floating about in the space station or on a space walk, they are falling (very nearly) as fast as if they had jumped off the Empire State building. However, to misappropriate Douglas Adams, they just keep missing the ground.

Which is why I brought up satilites too. If the shuttle is orbiting the earth and they are on a space walk, then they are also in orbit, meaning they are also a satilite in a perpetual fall. Thus, there is gravity in space.

[bonanova]

Gravity 101

Any two massive objects separated by a distance r share a mutually attractive gravitational force given by F_g = Gm₁m₂/r².

The net gravitational force on a single object is the vector sum of forces from all other objects in the universe.

Whether anything [atmosphere, asteroids, vacuum] exists in the intervening space is irrelevant.

Because the force behaves linearly with mass but falls off as the square of the distance, the force exerted by even large objects a great distance away can be negligible.

When the distance is not that large, the force exerted by a more massive object predominates.

Some familiar rock-paper-scissors comparisons:

• Moon beats Jupiter: The moon is tiny compared with planet Jupiter but much closer; so its gravitational force, not Jupiter's, creates tides.
  
• Sun beats Moon: Because of the Sun's extreme mass, Earth orbits it, rather than the nearer but much lighter moon.
  
• Earth beats Sun: Because Earth is close, the moon orbits Earth as the Earth-moon pair orbits the Sun.
  

[Guest]

Correction to the case of non-zero radius

t_f = ((D⁴- (r₁+r₂)⁴)/(6G(m₁+m₂)))^1/2