[[Ancient]]খৃষ্ট [[philosopher]]sপূ: as৫৫০ farমানত backথেলাচে asসংৰক্ষণশীলতাৰ [[Thales|Thalesথুলমুল ofধাৰণা Miletus]]আগবঢ়োৱা {{circa}}~550দেখা BCEপোৱা hadযায়, inklingsতেওঁৰ ofমতে theপ্ৰকৃতিত conservationএনে ofএক someপদাৰ্থ underlyingআছে substanceযিহেৰে ofবাকী whichসকলো everything is made. Howeverগঠিত, thereথেলাচে isপানীকে noএই particularপদাৰ্থ reasonবিধ toবুলি identifyধাৰণা thisকৰিছিল। withএম্পেড’কলচে what we know today as "mass(৪৯০-energy"৪৩০ (forখৃ: example, Thales thought it was waterপূ:).[[Empedocles]]মতে (490–430পৃথিৱী, BCE)জল, wroteবায়ু, thatআকাশেই inসকলো hisব্ৰহ্মাণ্ডীয় universalবস্তুৰ systemমূল, composedএই ofকেইটা [[Classicalধ্ৰুপডী element|fourপদাৰ্থৰ roots]]মিশ্ৰণ (earth,বা air,পৰিৱৰ্তনতেই water,ব্ৰহ্মাণ্ড fire),গঠন "nothing comes to be or perishes",হৈছে।<ref>{{cite journal|last=Janko|first=Richard|title=Empedocles, "On Nature"|journal=Zeitschrift für Papyrologie und Epigraphik|year=2004 |volume=150 |pages=1–26|url=http://ancphil.lsa.umich.edu/-/downloads/faculty/janko/empedocles-nature.pdf }}</ref> but these elements suffer continual rearrangement.
In 1638, [[Galileo Galilei|Galileo]] published his analysis of several situations—including the celebrated "interrupted pendulum"—which can be described (in modern language) as conservatively converting potential energy to kinetic energy and back again. However, Galileo did not state the process in modern terms and again cannot be credited with the crucial insight.
