Music, Math, and Motion Physics of Sound Ch.12 § 7-9 Dr. E.J. Zita The Evergreen St. College Winter week 8 Friday 27 Feb. 2009

Ch.12c: Doppler effect, Shock waves, and Applicaations Overview of 12b: § 7, 8, 9 Discuss sections Practice problems together Choose homework together? Looking ahead

Overview of Ch.12.7: Doppler Effect Both observers hear the same siren tone When the source is “fixed”, or not moving Who hears a higher frequency when the truck is moving? How much higher? Frequency of the source (firetruck siren) f never changes, but the perceived frequency f’ depends on what? Whether the truck is approaching you or moving away How fast Whether you are approaching a stationary truck? Would this be the same as the truck approaching you?

Overview of Ch.12.8: Shock waves and the Sonic boom

Overview of Ch 12.9 Applications: Sonar, Ultrasound, and Medical imaging Speed of sound in human tissue v ~ 1540 m/s (depends on what kind of tissue!), close to v water

Jigsaw learning-through-discussion 1. Count off by 7, 8, 9 Each team discuss your section Identify key points Zita will circulate, answering questions 2. Mix teams so there is one expert for each chapter on each team Discuss all sections – share your key points 3. Whole group gather: resolve questions, share insights and examples, and choose homework together

More on Ch.12.7: Doppler Effect

Truck moving away from stationary observer:

More on Ch.12.7: Doppler Effect Observer moving toward stationary source:

More on Ch.12.7: Doppler Effect for light is “Redshift” (or “blue shift”)

More on Ch.12.7: Doppler Effect for light is “Redshift” (or “blue shift”) Only the far right model fits observed evidence. Planets are discovered by observing red and blue shifts in the light of the star they orbit. Therefore, most of the planets discovered are very large and close to their parent star – the small or far ones have little Doppler effect.

More on Ch.12.8: Shock waves and the Sonic boom Cerenkov radiation and the Solar Neutrino Problem: one way to count the number of electron neutrinos ( ) coming from the Sun is to circulate cleaning fluid in a huge vat, counting how many Chlorines convert to Argon: p +  n + e 37 Cl +  36 Ar + e When electrons travel faster than light in cleaning fluid, they cause shock waves, emitting blue light. The orientation of the shock cone tells us the direction the e came from, and the the angle of the shock cone tells us the e speed /scientificamerican69.html

Why is Cerenkov light is blue? There are basically two reasons. In water, the blue light comes from excited atoms that emit blue light. The atoms in the water become excited by the Cerenkov shock wave and then de-excite, emitting blue light. In addition, the number of photons emitted by a Cerenkov electron is inversely proportional to wavelength (or proportional to the energy). Since these are high energy particles, this means that more photons are emitted with shorter wavelengths, thereby tilting the spectrum to the blue side. Amended from

More on Ch 12.9 Applications: Sonar, Ultrasound, and Medical imaging X-ray: echoing hi-energy (high-frequency, short-wavelength) electromagnetic waves – the first internal imaging technique, discovered accidentally by Roentgen in late 1800s. Ultrasound: high frequency (short-wavelength, therefore high- resolution) sound waves are bounced off hard and soft tissue, revealing internal details (such as fetal presence or deformity) CAT-scan (Computer-Aided Tomography) formerly known as EMI scan, developed by the music and recording business EMI. Provides detailed, cross-sectional views. PET scan (Positron Emission Tomography) measures radiation (positrons, gamma rays, or other particles) given off by the body after ingestion or injection of radioactive tracers. This enables dianosis of flows and dynamics in body, e.g. detection of cancer spread. MRI scan (Magnetic Resonance Imaging – formerly known as Nuclear magnetic resonance) In the presence of a strong background field, a second field of varying radio is rapidly oscillated. The different oscillations are absorbed preferentially by different tissues, revealing, for example, damage to bone, cartilage, soft tissue, or slipped disks.

Let’s try some HW together – you choose which

Problems from Ch.12-8

General Problems Ch Doppler Effect:Shock Waves:

Looking ahead