The Amazing Bow WaveZiyao ZhangAward: Top 100
School: shanghai qibaodwight high school This photo features a remote-controlled boat I made traveling in the water. I noticed some waves surrounding the boat when it was being driven in the water. The physics principle linked to this scenario is the Doppler effect. Behind the scene, I was standing on the ground as an observer and the moving boat was the source of the wave. At first, when the boat just started accelerating, the water was moving faster than the boat and the wavelength of the bow waves in front of the boat appeared smaller as the boat accelerated. We know that the velocity of the waves was relatively constant in a specific medium like water. Thus, when the boat accelerated until its velocity was greater than the velocity of the water waves, the wavelength of the bow waves increased. All the wavefronts that have bunched along a V-shaped envelope formed a cone-shaped compression called Mach cone, thus explaining the V-shaped bow waves I observed in the photo I took. As the difference between the velocity of the boat and the velocity of the water waves increases, the Mach cone angle will decrease and cause the bow to grow narrower. 
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