Seven words have split up into two sets because one set has changed and the other has not. To reunite them, change one letter of each of the words in the first set. While the result may not make a word, it will pair up with a word in the second group, either before or after it, to make a whole new word. When finished, anagram all seven replaced letters into a new word. As you may have guessed, all eight words belong to the same category. Can you name the words and, lastly, the category?
Set 1: rim fro lose tar sob far tun
Set 2: mat duct cant opera set tor gent
You matter. Until you multiply yourself by the speed of light squared. Then you energy.