ils ▁all ▁contribute ▁to ▁its ▁effect ▁on ▁the ▁applied ▁Force . ▁Where as ▁the ▁number ▁of ▁turns ▁of ▁co il , ▁its ▁size ▁( radius ) ▁and ▁the ▁amount ▁of ▁current ▁passing ▁through ▁it ▁determ ines ▁its ▁effect ▁on ▁the ▁App lied ▁Force . ▁The ▁spring ▁constant ▁depends ▁on ▁the ▁Young ' s ▁Mod ulus ▁of ▁the ▁moving ▁structure , ▁and ▁its ▁length , ▁width ▁and ▁thick ness . ▁ ▁Mag net ost rict ive ▁actu ators ▁Mag net ic ▁actu ation ▁is ▁not ▁limited ▁to ▁the ▁use ▁of ▁Lor ent z ▁force ▁to ▁cause ▁a ▁mechanical ▁disp lacement . ▁Mag net ost rict ive ▁actu ators ▁can ▁also ▁use ▁the ▁theory ▁of ▁magnet ism ▁to ▁bring ▁about ▁disp lacement . ▁Material s ▁that ▁change ▁their ▁shapes ▁when ▁exposed ▁to ▁magnetic ▁fields ▁can ▁now ▁be ▁used ▁to ▁drive ▁high - re li ability ▁linear ▁mot ors ▁and ▁actu ators .. ▁An ▁example ▁is ▁a ▁nick el ▁rod ▁that ▁tends ▁to ▁de form ▁when ▁it ▁is ▁placed ▁in ▁an ▁external ▁magnetic ▁field . ▁Another ▁example ▁is ▁wrapping ▁a ▁series ▁of ▁elect romagnet ic ▁induction ▁co ils ▁around ▁a ▁metal ▁t ube ▁in ▁which ▁a ▁Ter fen ol - D ▁material ▁is ▁placed . ▁The ▁co ils ▁generate ▁a ▁moving ▁magnetic ▁field ▁that ▁courses ▁w av eli ke ▁down ▁the ▁success ive ▁wind ings ▁along ▁the ▁stat or ▁t ube . ▁As ▁the ▁travel ing ▁magnetic ▁field ▁causes ▁each ▁succeed ing ▁cross ▁section ▁of ▁Ter fen ol - D ▁to ▁el ong ate , ▁then