Question

Write the characteristics of nuclear force. How is it different from gravitational and electric (electrostatic) forces?

Hint:

Recall that the nuclear force is the strongest force in nature, acts only over a few femtometres, is charge independent, and saturates, unlike the long-range gravitational and electric forces.

Answer 1

Concept: The nuclear force is the strong attractive force that binds protons and neutrons (nucleons) together inside a nucleus, in spite of the strong electrostatic repulsion between the positively charged protons.

Characteristics of nuclear force:
1. Strongest force in nature: At nuclear distances it is about 100 times stronger than the electrostatic force and about \(10^{38}\) times stronger than the gravitational force.
2. Short range: It acts only up to a distance of about \(2\text{ to }3\ \text{fm}\) (\(1\ \text{fm}=10^{-15}\ \text{m}\)). Beyond a few femtometres it becomes practically zero.
3. Charge independent: The force between neutron and neutron, proton and neutron, and proton and proton (nuclear part only) is the same. It does not depend on the charge of the nucleons.
4. Attractive and repulsive: It is strongly attractive for separations greater than about \(0.7\ \text{fm}\), but becomes repulsive for separations smaller than \(0.7\ \text{fm}\). This repulsive core keeps the nucleus from collapsing.
5. Saturated (short-range saturation): A nucleon interacts only with its nearest neighbours, not with every other nucleon in the nucleus. This is why binding energy per nucleon is almost constant for medium and heavy nuclei.
6. Non-central and spin dependent: The force depends on the relative orientation of the spins of the nucleons, so it is not purely a central force.

Difference from gravitational force:
• Nuclear force is about \(10^{38}\) times stronger.
• Nuclear force is very short range (\(\sim\text{few fm}\)); gravitation has infinite range.
• Gravitation is always attractive and depends on mass; nuclear force can be attractive or repulsive and is independent of charge/mass type.

Difference from electric (electrostatic) force:
• Nuclear force is about 100 times stronger at nuclear distances.
• Electric force is a long-range inverse-square force; nuclear force acts only over a few fm.
• Electric force acts only between charged particles and can be attractive or repulsive depending on sign; nuclear force is charge independent and acts between all nucleons.

\[\boxed{\text{Nuclear force: strongest, short range }(\sim2\text{ fm}),\ \text{charge independent, saturated}}\]