What is the nuclear force? State its important properties.

1. 1 · Define it. The strong attractive force that holds protons and neutrons together inside a nucleus.
2. 2 · Say why it is needed. Protons repel each other, and gravity is far too weak to hold them.
3. 3 · List the properties.
   • Strongest force; gravity is about 10⁻³⁹ times weaker
   • Short range, about 10⁻¹⁵ m
   • Charge independent
   • Saturates: acts only between neighbours
   • Repulsive at very short distances
4. 4 · Draw the graph. [Graph: force against distance; repulsion at very small r, attraction around 1 fm, zero beyond a few fm]
5. 5 · Close in one line. So, the nuclear force beats electric repulsion only at nuclear distances.

Scoring tip: Two or three properties stated clearly, each with its key word, are enough for 3 marks.