Sound Waves

• Sound is a form of energy caused by vibration.
• Sound can propagate through a liquid, solid and gas, but not through a vacuum.
• A bell is rung, the metal surface of the bell will vibrate, and air molecules near the surface will also vibrate and collide with the air molecules nearby.
• Vibration is transferred from one molecule to another molecule beside it in the form of waves.
• Sound is heard by the ears of the listener.
• Sound requires a medium to propagate.
• Sound propagates at different speeds in different mediums such as air, water, and flour.
• In solids, sound vibrations travel very rapidly when the particles at one end of the solid start to vibrate, causing the nearby particles to also vibrate as the particles of solids are arranged very closely together.
• In liquids, sound vibrations travel less rapidly due to the loose arrangement of particles.
• In gases, sound waves propagate very slowly because the arrangement of gas particles which are far apart from each other causes a delay in the transfer of vibration.
• The amount of sound reflected or absorbed depends on the surface of the object.
• Good sound reflectors are hard and smooth surfaces, while good sound absorbers are soft and rough surfaces.
• In a bedroom, blankets, carpets, and curtains are good sound absorbers.
• Our ears can differentiate the sounds that are heard because sounds have different strengths and pitches.
• Loudness of sound depends on the amplitude of sound wave.
• Pitch of sound depends on the frequency of the sound produced and is measured in the unit of hertz (Hz).
• Loudness of sound increases when wave amplitude increases.
• Pitch of sound increases when wave frequency increases.
• The Doppler effect is the apparent change in frequency caused by the relative movement of a sound source, the relative movement of the observer or both.
• Frequency of an ambulance siren heard by the observer increases when the ambulance approaches the stationary observer.
• Frequency of an ambulance siren heard by the observer decreases when the ambulance drives away from the stationary observer.