Waves interact with matter in several ways. The interactions can occur when waves pass from one medium to another, meet a barrier, or spread out around an edge or gap in a medium. Some examples of interactions are reflection, refraction, and diffraction.   Diffraction: The reason you can hear sounds around corners is that sound waves spread out and travel around obstacles. This is called diffraction. It also occurs when waves pass through an opening in an obstacle. All waves may be diffracted, but it is more pronounced with some types of waves than others. For example, sound waves spread... Show more

Waves interact with matter in several ways. The interactions can occur when waves pass from one medium to another, meet a barrier, or spread out around an edge or gap in a medium. Some examples of interactions are reflection, refraction, and diffraction.
 

Diffraction: The reason you can hear sounds around corners is that sound waves spread out and travel around obstacles. This is called diffraction. It also occurs when waves pass through an opening in an obstacle. All waves may be diffracted, but it is more pronounced with some types of waves than others. For example, sound waves spread out around corners much more than light does. That's why you can hear but not see around corners.    
For a given type of waves, such as sound waves, how much the waves diffract depends on two factors: the size of the obstacle or opening in the obstacle and the wavelength of the waves.    
- Diffraction is minor if the length of the obstacle or opening is greater than the wavelength.    
- Diffraction is major if the length of the obstacle or opening is less than the wavelength.    

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