• Question: What is the difference between the weak nuclear force and the strong nuclear force?

    Asked by stormwhite to Arttu, Ceri, James_M, Monica, Philip on 20 Jun 2011.
    • Photo: Arttu Rajantie

      Arttu Rajantie answered on 20 Jun 2011:

      The are actually two completely different forces, but we tend to group them together because they both work only at short distances and are therefore only relevant for nuclear physics. Strong force binds quarks together to form protons and neutrons, and also protons and neutrons together to form atomic nuclei. Weak force allows quarks to turn into other quarks, which can turn a neutron into a proton and break up the nucleus. This causes radioactivity.

    • Photo: James M Monk

      James M Monk answered on 20 Jun 2011:

      One big difference is that the particles/fields that are responsible for carrying the strong force are massless, whereas for the weak force they are quite massive (nearly 100 times the proton mass). This explains why the weak force is weak – it is quite hard to borrow that much mass-energy for long enough to propagate very far.

      Like the weak force, the strong force is limited in its range. The reason is very different, though. The weak force is limited by the mass of its force carrier, whereas the strong force is limited in range because it is so strong that you cannot have an isolated quark – if you tried to pull a quark out of a proton it would take so much energy that you would generate more quarks, which would bind with the one you were trying to isolate. So you can never have a single quark on its own

      Another difference is that the strong force actually gets weaker as you go up in energy, whereas the weak force gets stronger – at very high energy they should have the same strength.

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