#!/usr/bin/env python
# coding: utf-8

# # Oscillations and sound
# 
# ### Experiments

# The oscillations of a body can generate sound waves in air. This is the case of musical instruments, but is also the case of other objects, as we can see in the following experiment.

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from IPython.display import Video
Video('./video/KostaBoda.mp4', width = 600)


# The sound produced depends on the characteristics of the body, which behaves as the source of mechanical waves.
# 
#  

# In[14]:


from IPython.display import Video
Video('./video/Kristall.mp4', width = 600)


# ### Analysis
# 
# Now we can analyze the sound. To this aim we can use the Audacity app.
# 
# <a href="https://www.audacityteam.org/">
# <img src="./img/audacity_logo.png" alt="audacity_logo" width="100"/> 
# </a>
# 
# We can import the file and look at the signal that has been recorded. The audio wave forces the membrane of the microphone to vibrate. The microphone acts as a **transducer**, generating a time dependent voltage that is proportional to the displacement of the membrane.
# 
# <img src="./img/Sound001.png" alt="Plot Audio Signal" width="800"/>

# Looking in greater detail, we observe a kind of complex fluctuation. 
# 
# For comparison, using Audacity, we show it in the figure here below, along with a pure sinusoidal function.
# 
# <img src="./img/Sound001_detail.png" alt="FourierSpectrum" width="800"/>

# We can describe the recorded sound as a superposition of different sinusoidal functions, applying the **Fourier analyis**.
# 
# <img src="./img/Spectrum_sound001.png" alt="drawing" width="500"/>
# 

# This plots (obtained using Audacity) represents the amplitude of the sinusoidal functions at different frequencies, whose sum will better describe the given signal.
# 
# We can observe that the sound has an intense component at about 823 Hz, and other components at 342 Hz, and 1440 Hz, respectively.

# ### A surprising effect
# 
# #### <span style="color:blue"> Resonance </span>
# 
# Now we can use te Audacity App to generate a continuous wave at 823 Hz, and play this sound close to the object that we have considered above. Suppose that we play the sound for 3 seconds
# 
# * When the sound at 823 Hz is turned off **we can still ear a weak sound at the same pitch, coming from the object**
#     * What is going on?
#     
#  > We have put the object in oscillation. The sound wave makes the object vibrate at this particular frequency, that is a frequency at which that body **can** oscillate. Once the body oscillates, it can itself generate a sound wave at that frequency, since it can transfer its motion to the air molecules near to its walls.

# &nbsp;
# 
# ### Copyright and License
# --------------------------
# (c) 2022 Andrea Mandanici, Giuseppe Mandaglio, Giovanni Pirrotta, Valeria Conti Nibali, Giacomo Fiumara. All content is under Creative Common Attribution  <a rel="license" href="https://creativecommons.org/licenses/by/4.0"> CC BY 4.0 </a> 
#  and all code is under [BSD 3-Clause License](https://opensource.org/licenses/BSD-3-Clause).

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