Answer
a. We know that the strong force exists because of the observed behavior of atomic nuclei.
b. The strong force is short-range because it acts only over very short distances, typically on the order of a few femtometers (10^-15 meters). This is much shorter than the range of the electromagnetic force, which acts over much larger distances.
Work Step by Step
a. The strong force is responsible for holding protons and neutrons together in the nucleus, and it is a fundamental force of nature that is one of the four known fundamental interactions of nature, along with gravity, electromagnetism and the weak force.
b. One way to know the short-range behavior of strong force is to observe the scattering of protons or neutrons in a bubble chamber. At short distances, the protons and neutrons are strongly affected by the strong force, which results in a large number of scatterings. But as the distance increases the number of scatterings decrease and eventually stops, showing the short-range behavior of the force. Another way is to measure the forces between protons and neutrons inside nuclei by looking at the energy levels of nuclei and comparing the results to predictions based on models of the strong force.
