| Although the total energy of a system does not change with time, its value may depend on the [[frame of reference]]. For example, a seated passenger in a moving airplane has zero kinetic energy relative to the airplane, but non-zero kinetic energy relative to the [[Earth]]. | | Although the total energy of a system does not change with time, its value may depend on the [[frame of reference]]. For example, a seated passenger in a moving airplane has zero kinetic energy relative to the airplane, but non-zero kinetic energy relative to the [[Earth]]. |
− | <center>For lessons on the topic of '''''Energy''''', follow [http://nordan.daynal.org/wiki/index.php?title=Category:Energy this link].</center> | + | <center>For lessons on the topic of '''''Energy''''', follow [https://nordan.daynal.org/wiki/index.php?title=Category:Energy this link].</center> |
| The word ''energy'' derives from Greek ''ἐνέργεια'' (''energeia''), which appears for the first time in the work [http://www.perseus.tufts.edu/cgi-bin/ptext?doc=Perseus%3aabo%3atlg%2c0086%2c010%3a1098b%3a33&vers=original&word=e%29ne%2frgeia#word1 "Nicomachean Ethics"] by [[Aristotle]] in the 4th century BC. In 1021 AD, the Arabian [[physics|physicist]], [[Ibn al-Haytham|Alhazen]], in the ''Book of Optics'', held [[light]] rays to be streams of minute energy particles, stating that "the smallest parts of light" retain "only properties that can be treated by geometry and verified by [[experiment]]" and that "they lack all sensible qualities except energy." In 1121, [[Al-Khazini]], in ''The Book of the Balance of Wisdom'', proposed that the gravitational potential energy of a body varies depending on its distance from the centre of the Earth. (Encyclopedia of the History of Arabic Science ISBN 0415124107 | | The word ''energy'' derives from Greek ''ἐνέργεια'' (''energeia''), which appears for the first time in the work [http://www.perseus.tufts.edu/cgi-bin/ptext?doc=Perseus%3aabo%3atlg%2c0086%2c010%3a1098b%3a33&vers=original&word=e%29ne%2frgeia#word1 "Nicomachean Ethics"] by [[Aristotle]] in the 4th century BC. In 1021 AD, the Arabian [[physics|physicist]], [[Ibn al-Haytham|Alhazen]], in the ''Book of Optics'', held [[light]] rays to be streams of minute energy particles, stating that "the smallest parts of light" retain "only properties that can be treated by geometry and verified by [[experiment]]" and that "they lack all sensible qualities except energy." In 1121, [[Al-Khazini]], in ''The Book of the Balance of Wisdom'', proposed that the gravitational potential energy of a body varies depending on its distance from the centre of the Earth. (Encyclopedia of the History of Arabic Science ISBN 0415124107 |