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

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  • #1
garylau
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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
 

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  • #2
BvU
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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.
 
  • #3
garylau
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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?
 
  • #4
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).
 
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  • #5
BvU
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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.
 
  • #6
garylau
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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?
 
  • #7
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is it possible that the mass is very large but the r is very small?
Yes. Moreover, in quantum physics mass is, in a certain sense, proportional to ##1/r##.
 
  • #8
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is it possible that the mass is very large but the r is very small?
Yes, then you get a very large force. But it is always finite. And if you want to put the masses too close, you have to consider quantum mechanics where the simple approach with a well-defined distance fails.
 

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