Tap the cups in turn with a thin stick. The water in the cup is different, the vibration speed of the cup and the water is different, and the sound tone produced by the vibration of the cup and the water is also different, so ② should be: tone.
(2) Sound waves with frequencies below 20Hz are called infrasound waves, so infrasound waves refer to infrasound waves that we have learned.
(3) Only when the vibration frequencies of two objects are the same can * * * vibration occur. The vibration frequency of infrasound is lower than 20Hz, so the natural frequency of human internal organs is around 20Hz.
Sound waves have energy because they can destroy internal organs.
(4) The tone of sound is related to frequency; The higher the frequency of sound source vibration, the higher the tone of sound.
So the answer is: (1)① ultrasound; 2 tone.
(2) infrasound waves.
(3)20Hz； Energy.
(4) frequency; The higher the frequency of sound source vibration, the higher the tone of sound.