# What happen if i put r=0 into the formula F=(k)mm/r^2

• B
garylau
What happen if i put r=0 into the formula F=(k)mm/r^2
So 1/0=infinity ?

then F= infinite large in mathematical sense?
is that statement correct ?

thank

## Answers and Replies

Homework Helper
That's what happens with the formula. In reality you can't have two masses in exactly one place, so the formula isn't endlessly applicable...

Mathematically you have a singularity.

garylau
That's what happens with the formula. In reality you can't have two masses in exactly one place, so the formula isn't endlessly applicable...

Mathematically you have a singularity.
But In reality i can have two mass put in r=0.000001m
So the force still become very large?

What happen if i put r=0 into the formula F=(k)mm/r^2

then F= infinite large in mathematical sense?
is that statement correct to say F is infinitely large?

You cannot put in r = 0. That does not make sense. It does make sense to consider:

##\lim_{r \to 0}F = +\infty##. This means, intuitively, when ##r## approaches ##0##, ##F## becomes larger and larger (F grows without bound).

• PeroK and garylau
Homework Helper
But In reality i can have two mass put in r=0.000001m
So the force still become very large?
Well, the masses become smaller too for such small particles. One micron diameter with a reasonable density gives a very small mass !

On even smaller scales still other things happen. Protons, for example have a mass of only 1.67 10-31 kg and a diameter of 0.88 10-15 m. At such small scales other kinds of forces are much stronger.

• garylau
garylau
Well, the masses become smaller too for such small particles. One micron diameter with a reasonable density gives a very small mass !

On even smaller scales still other things happen. Protons, for example have a mass of only 1.67 10-31 kg and a diameter of 0.88 10-15 m. At such small scales other kinds of forces are much stronger.
is it possible that the mass is very large but the r is very small?