( ( In physics ) ( , ( ( ` ( ultrasound ' ) ) ( ( refers ( to ( ( ( ( sound waves ) ( with ( ( a frequency ) ( too high ) ) ) ) ( for humans ) ) ( to hear ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NN physics))) (, ,) (NP (`` `) (NN ultrasound) ('' ')) (VP (VBZ refers) (S (VP (TO to) (VP (VB sound) (NP (NNS waves)) (PP (IN with) (NP (NP (DT a) (NN frequency)) (ADJP (RB too) (JJ high)))) (PP (IN for) (NP (NNS humans))) (S (VP (TO to) (VP (VB hear)))))))) (. .)))
In physics, 'ultrasound' refers to sound waves with a frequency too high for humans to hear.
(ROOT (S (NP (PRP You)) (VP (VBP call) (NP (NP (NN sound)) (SBAR (WHNP (WDT that)) (S (VP (VBZ has) (S (NP (DT a) (NN wave) (NN frequency)) (ADJP (JJR higher) (SBAR (IN than) (S (NP (DT the) (JJ human) (NN ear)) (VP (MD can) (VP (VB detect) (NP (NN ultrasound))))))))))))) (. .)))