Question

why the gravitational force is always attractive? why not repulsive?

Answer 1

Because when I travel in the vicinity of something with mass, my world-line travels along a geodesic projected by the said mass (in 4D into 3D). A simplified form of this is by introducing gravity as a force, but gravity is really just "curved" spacetime.

This is all I learned in class. There are other things, like stress-energy tensors, that you should read up on if you're really interested.

Answer 2

(Disclaimer: I don't know anything about tensors.)

Answer 3

You know I read that the equation of forces between masses is same as electrical forces between charges, Electrical forces are both in nature attractive as well as repulsive, but why only gravity is attractive in nature

Answer 4

masses are always positive.

Answer 5

Though we may have observed and reasoned that charge can be positive and negative, we have not come across cases of negative mass, although there was something a short while back with the Casimir effect in quantum--simulating negative mass.

This is all we can methodically, rationally know about the universe. Up to modern college physics, of course.

Answer 6

(In my limited knowledge and experience.)

Answer 7

How much our world of knowledge is limited without modern physics....

Answer 8

Modern Physics is a college class. :D I am in no way a fully trained PhD in physics. Though I might wish otherwise.

Answer 9

No problem yaar, you'd be better learning now that

Answer 10

Sir, tell me I am a Diploma electrical engg. student, I want to read quantum physics and relativity in depth, so what should I choose my path.....This is my final semester, I am reading about the Special relativity which keeps my interest more high. and helps me to understand better electricity

Answer 11

one qualitative explanation that i can give is it that we are bound to the earth with some negative energy associated with it (electrons have negative energy and hence is bound to the positive nucleus)
quantitative explanation: that is why we write gravitational potential energy as -GMm/r

Answer 12

Salini any another expalnation, your answer doesn't reaches my expectation

Answer 13

gravitational potential energy is always 0 at an infinite distance, so anywhere in between will give a negative answer.

Answer 14

It not the gravitational potential energy that pulls. Its something else, which creates a pull around itself, its is directly proportional to product of two body masses thats anoying thing.

Answer 15

it is just taht the SUM of p.e and k.e becomes 0 at infinity when the mechanical energy(total) becomes zero and as this TOTAL ENERGY expression is not -ve we can be convinced to say that a body is attached,bound to the earth(negative forces are attractive)
whenever we say a body has energy in terms of its motion it points to the toatl mechanical energy
so when this sum is -ve the body is bound to earth