Summary of knowledge points in the second chapter of the eighth grade of physics in the humanistic version of the first book

1. The occurrence and propagation of sound

The generator is vibrating - experiment; sound propagates by medium - medium: all solids, liquids, and gases; vacuum cannot transmit sound

Speed of sound - -velocity of sound in air (about 340 m/s); general, velocity in solids > velocity in liquids > velocity in gases; velocity of sound increases with temperature

Echo - time and distance required for echo; applications

Calculations -In conjunction with travel problems

2. Pitch, loudness, and timbre

Objective quantities - frequency (note range of human hearing and range of vocalization), amplitude

Subjective quantities - -pitch, loudness (the meaning of high and low size); factors affecting loudness: amplitude, distance, degree of dispersion

Tone - the role; tone is determined by the sound-producing body itself

3. Hazards and control of noise

Noise -Physical and life noise (physical - irregular vibration, life - sound that affects work, study, rest); noise level: decibel (0dB - just caused by hearing); methods to reduce noise (at the sound source, in the process of propagation, the human ear); the four major pollution (air pollution, water pollution, solid waste pollution, noise pollution)