MadSci Network: Physics
Query:

Re: How big is the gravitational force between nucleons?

Date: Wed Jun 7 08:42:52 2000
Posted By: David North, Staff, Medical Physics, Rhode Island Hospital
Area of science: Physics
ID: 960226793.Ph
Message:

Gravity is so weak a force that it has no noticeable effect on what happens 
in a nucleus. So far (!) there are four known forces in nature which can 
affect us, leaving aside questions of unification theories. They are: 
gravity, electromagnetism, the "strong" nuclear force, and the "weak" 
nuclear force. On a scale which assigns a strength of 1.0 to the
electromagnetism between two protons in a nucleus, the "strong" force  has 
a relative strength of 20, and the "weak" force has a strength of 10exp-7. 
However, both of those operate only over very short ranges, on the order of 
10exp-12 centimeters, which is a typical separation between nucleons in a 
nucleus. The "weak" force is responsible for some types of radioactivity, 
and the "strong" force holds the nucleus together. Gravity on this scale 
has a strength of about 10exp-36, even though it has an infinite range like 
electromagnetism. The reason gravity can do the things we observe, such as 
make weights fall to the ground and the Moon orbit the Earth, is that the 
masses involved are so enormous compared to that of a nucleus.


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