▁Sun , ▁the ▁process ▁of ▁hydro gen ▁fusion ▁converts ▁about ▁ 4 ▁million ▁t onnes ▁of ▁solar ▁matter ▁per ▁second ▁into ▁elect romagnet ic ▁energy , ▁which ▁is ▁radi ated ▁into ▁space . ▁ ▁Forces ▁and ▁potential ▁energy ▁Pot ential ▁energy ▁is ▁closely ▁linked ▁with ▁forces . ▁If ▁the ▁work ▁done ▁by ▁a ▁force ▁on ▁a ▁body ▁that ▁moves ▁from ▁A ▁to ▁B ▁does ▁not ▁depend ▁on ▁the ▁path ▁between ▁these ▁points , ▁then ▁the ▁work ▁of ▁this ▁force ▁measured ▁from ▁A ▁assign s ▁a ▁scalar ▁value ▁to ▁every ▁other ▁point ▁in ▁space ▁and ▁defines ▁a ▁scalar ▁potential ▁field . ▁In ▁this ▁case , ▁the ▁force ▁can ▁be ▁defined ▁as ▁the ▁negative ▁of ▁the ▁vector ▁gradient ▁of ▁the ▁potential ▁field . ▁ ▁For ▁example , ▁gravity ▁is ▁a ▁conserv ative ▁force . ▁The ▁associated ▁potential ▁is ▁the ▁gravit ational ▁potential , ▁often ▁denoted ▁by ▁ ▁or ▁, ▁corresponding ▁to ▁the ▁energy ▁per ▁unit ▁mass ▁as ▁a ▁function ▁of ▁position . ▁The ▁gravit ational ▁potential ▁energy ▁of ▁two ▁particles ▁of ▁mass ▁M ▁and ▁m ▁separated ▁by ▁a ▁distance ▁r ▁is ▁ ▁The ▁gravit ational ▁potential ▁( specific ▁energy ) ▁of ▁the ▁two ▁bodies ▁is ▁ ▁where ▁ ▁is ▁the ▁reduced ▁mass . ▁ ▁The ▁work ▁done ▁against ▁gravity ▁by ▁moving ▁an ▁inf init es imal ▁mass ▁from ▁point ▁A ▁with ▁ ▁to ▁point ▁B ▁with ▁ ▁is ▁ ▁and ▁the ▁work ▁done ▁going ▁back ▁the ▁other ▁way ▁is ▁ ▁so ▁that ▁the ▁total ▁work ▁done ▁in ▁moving ▁from ▁A ▁to ▁B ▁and ▁returning ▁to