======Doppler Effect with Water Waves======


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**Alternative titles:** Water Tank Doppler Demonstration
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====Summary====                   
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====Procedure====  
  - Fill a shallow tray or ripple tank with water.  
  - Create waves using a small object (such as a vibrating dipper, stick, or finger) placed in the water at a fixed point. Observe the circular wavefronts radiating evenly in all directions.  
  - Begin moving the wave source slowly across the water while continuing to make ripples.  
  - Notice that in the direction of motion, the wavefronts are closer together (higher frequency), while behind the motion they are farther apart (lower frequency).  
  - Compare the spacing perpendicular to the motion, which remains unchanged.



====Links==== 
Ripple Tank Speed, Frequency, Doppler Effect - Ken Sadowsky: 
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====Variations====
  * Change the speed of the moving wave source to observe how the degree of wave compression changes.  
  * Use two moving sources to show overlapping Doppler patterns.  
  * Record the waves with a camera and analyze spacing of wavefronts using software.  
  * Compare water wave Doppler patterns to sound Doppler shifts with a siren or Doppler ball.



====Safety Precautions====
  * Keep electrical equipment (if using a ripple tank with a vibrator) away from water spills.  
  * Wipe up any water splashes to avoid slipping hazards.  
  * Handle glass or plastic tanks carefully to prevent breakage.




====Questions to Consider====
  * Why are wavefronts closer together in front of the moving source? (The source is moving into its own waves, compressing them and increasing frequency.)  
  * Why are wavefronts farther apart behind the moving source? (The source moves away from previously emitted waves, stretching them to lower frequency.)  
  * How does this demonstration relate to sound or light? (The same Doppler principle applies to all waves, explaining changes in siren pitch and redshift in astronomy.)  
  * What happens if the wave source moves faster than the waves themselves? (A shockwave forms, similar to a sonic boom.)