Changes

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>

==History==

==History==

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