A Level Physics Practice Exam

What happens to the strong nuclear force at distances closer than 0.5fm?

1. It remains attractive

2. It becomes repulsive

3. It changes to gravitational force

4. It ceases to exist

The correct answer is: It becomes repulsive

At distances closer than 0.5 femtometers (fm), the strong nuclear force experiences a significant change in behavior; it becomes repulsive. This phenomenon occurs because the strong nuclear force, which is responsible for holding protons and neutrons together in an atomic nucleus, is mediated by particles called gluons. At very short ranges, the intense forces among the nucleons (protons and neutrons) due to the gluons and the high concentration of energy result in a repulsive interaction. This repulsion is crucial in preventing the collapse of the nucleus, as it counteracts the attractive forces that dominate at slightly greater distances. When nucleons are too close to each other, the repulsive force acts to keep them apart, ensuring stability within the atomic nucleus. Thus, the strong nuclear force not only has attractive components at larger distances but also incorporates strong repulsive components when nucleons are forced into very close proximity. This understanding is key in nuclear physics as it describes the balance of forces that govern nuclear stability.