Pumpkin Doppler Analysis

1
Pumpkin Doppler Analysis

• Use either .wav or .mp3 files from 2004 on course
  web page, or filtered file from earlier year on
  my home page http//www.physics.odu.edu/hyde/chw.h
  tm
• Open files in cool edit (available in Rm 224) or
  download Free Tryout of Adobe Audition (requires
  Windows2000), http//www.adobe.com/products/auditi
  on/main.html
• on left, click on "Tryout"
• Fill out registration,
• download time 2 hrs at 56K, 17 min at DSL
• Adobe Audition is the update to CoolEdit
  (formerly from Syntrillium.com)

2
Instructions for Cool EditSee Lab 4 Lab 8 on
course homepageOpen .wav or .mp3 file in cool
edit
Splat
Use Cursor to select a region of width 0.1 sec
Go to Analyze menu, select Frequency Analysis
3
Frequency Analysis

• Select FFT size at least 4096.
• Re-Scan
• Record Frequency of siren, from here,
• check by placing cursor on peak.

4
Tabulate data

• Make a table of the frequency of the siren at
  different times during the fall. Work backwards
  from the splat, with intervals of 0.1 sec near
  the end, and larger time steps at the beginning
  (This table is only representative)

5
Calculate PumpkinVelocity from Doppler Effect

• f(ti) f0 / (1 vi/c)
• f0 frequency of siren at beginning (before
  drop).
• c speed of sound 342 m/s
• f(ti) measured frequency at time ti.
• vi velocity of pumpkin at time ti.
• Negative approaching microphone (falling down)
• Solve for velocity
• Vi c f0/f(ti)-1
• Add to table.
• Compare to free fall formula v(t) (-9.8 m/s2)
  (t-t0)
• t0 time pumpkin is released.