The four fundamental forces of nature, listed in order of decreasing strength, are:
The strong nuclear force is the strongest, with a relative strength of about
1.
The electromagnetic force is next, with a relative strength of about
10−2.
The weak nuclear force follows, with a relative strength of about
10−13.
The gravitational force is the weakest, with a relative strength of about
10−38 (taking the proton–proton gravitational attraction at
r=10−15 m).
Therefore, the gravitational force is the weakest fundamental force.
Hence, the correct option is
Gravitational force.
