What are sound waves?
Sounds are produced by vibrations.
Sound travels as waves, which are vibrating particles.
Sound waves are reflected by surfaces.
How is sound produced?
When you bang a drum its skin vibrates. The harder you bang, the bigger the vibrations. The vibrating drum skin causes nearby air particles to vibrate, which in turn causes other nearby air particles to vibrate. These vibrating particles make up a sound wave.
How does sound travel?
Sound waves travel at 343 m/s through the air and faster through liquids and solids. The waves transfer energy from the source of the sound, e.g. a drum, to its surroundings. Your ear detects sound waves when vibrating air particles cause your ear drum to vibrate. The bigger the vibrations the louder the sound.
Reflection of sound
Surfaces reflect sound waves:
Hard surfaces reflect sound well, making echoes.
Soft surfaces, like curtains and carpets, reflect very little sound. They absorb the sound instead, so there are no echoes.