Seek time is the time required to move the disk arm to the required track. Rotational delay or latency is the time it takes for the beginning of the required sector to reach the head. Sum of seek time (if any) and latency is the access time. Time taken to actually transfer a span of data is transfer time.
The transformation of Hydrogen atoms into Helium atoms with an emission of vast amount of energy is called nuclear fusion which is the source of energy for the Sun.