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

  • B
  • Thread starter garylau
  • Start date
  • #1
70
3

Main Question or Discussion Point

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

  • #2
BvU
Science Advisor
Homework Helper
2019 Award
12,858
2,952
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
70
3
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
Math_QED
Science Advisor
Homework Helper
2019 Award
1,364
491
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).
 
  • #5
BvU
Science Advisor
Homework Helper
2019 Award
12,858
2,952
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
70
3
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
Demystifier
Science Advisor
Insights Author
10,605
3,344
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
33,888
9,607
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.
 

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

  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
6
Views
3K
Replies
6
Views
3K
  • Last Post
Replies
1
Views
1K
Replies
2
Views
13K
Replies
6
Views
9K
Top