The Strong Nuclear Force
- In the nucleus, there are electrostatic forces between the protons due to their electric charge and gravitational forces due to their mass
- Comparatively, gravity is a very weak force and the electrostatic repulsion between protons is therefore much stronger than their gravitational attraction
- If these were the only forces, the nucleus wouldn’t hold together
- Therefore, the force that does hold the nucleus together is called the strong nuclear force
- The strong nuclear force keeps the nucleus stable since it holds quarks together
- Since protons and neutrons are made up of quarks, the strong force keeps them bound within a nucleus
Whilst the electrostatic force is a repulsive force in the nucleus, the strong nuclear force holds the nucleus together
Range of the Strong Nuclear Force
- The strength of the strong nuclear force between two nucleons varies with the separation between them
- This can be plotted on a graph which shows how the force changes with separation
The strong nuclear force is repulsive before a separation of ~ 0.5 fm and attractive up till ~ 3.0 fm
- The key features of this graph are that the strong nuclear force is:
- Repulsive closer than around 0.5 fm
- Attractive up to around 3.0 fm
- Reaches a maximum attractive value at around 1.0 fm (the typical nuclear separation)
- Becomes zero after 3.0 fm
- In comparison to other fundamental forces, the strong force therefore has a very small range (only up to 3.0 fm)
Examiner Tip
- You may see the strong nuclear force also referred to as the strong interaction
- Remember to write that after 3 fm, the strong force becomes 'zero' or 'has no effect' rather than it is ‘negligible’.
- Recall that 1 fm = 1 × 10–15 m
