Final answer:
Nuclear fusion requires high temperatures and high densities primarily to overcome the repulsive force between protons. Additionally, high temperatures are needed because fusion produces a significant amount of energy, and high densities are necessary to create enough collisions for fusion to occur.
Step-by-step explanation:
The primary reason why nuclear fusion requires high temperatures and high densities is to overcome the repulsive force between the protons. The electric repulsion between protons is incredibly strong and needs to be overcome in order to get them close enough to induce fusion. The high temperatures and densities provide the necessary kinetic energy to overcome this repulsion and allow the protons to combine, release energy, and undergo fusion.
Another reason why high temperatures are required is because fusion produces a significant amount of energy. When the nuclei fuse together, some of their mass is converted into energy. To achieve the temperatures necessary for fusion, heat is applied to the fusion fuel, causing the protons to move at high speeds and collide with enough energy to overcome the repulsion and initiate fusion.
Finally, high temperatures and densities in nuclear fusion are essential in order to create enough collisions between particles for fusion to occur. In a high-temperature and high-density environment, there are more particles moving at high speeds, increasing the chances of collisions and fusion reactions.