Lect08

# Lect08 - PHYS 172 Modern Mechanics Fall 2009 Lecture 9...

This preview shows pages 1–7. Sign up to view the full content.

Fall 2009 PHYS 172: Modern Mechanics Lecture 9 – Harmonic Oscillators, Sound, Circular Motion Read 4.14 – 4.20

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Today’s Lecture •The Harmonic Oscillator • Speed of Sound in Solids • Circular Motion
CLICKER QUESTION #1 Reading Question (Sections 4.14 – 4.20) (This is a closed-book quiz, no consulting with neighbors, etc.) In our spring-mass model of solids, we can make a reasonable guess as to the speed of sound, V s . We find that V s depends on: A. the atomic mass and the spring constant. B. The angular frequency and distance between atoms. C. the amplitude of each atom’s harmonic motion. D. the frequency of oscillation

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
A Mechanism For Contact Forces: Tension The heavier the ball, the more the wire has to pull upwards. How does the wire “know” how to do this? The more you stretch a spring, the harder it pulls back!
T F L strain = ; stress = L A ! ( ) ( ) 2 s k / ; atomic version Y = / s T s d k F L Y A L s d d ! = = Young’s modulus can be expressed in terms of the atomic spring constant: Young’s Modulus

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
What is the distance between atoms in a simple solid? Assume you have 1cubic cm ( 1 cm 3 ) of aluminum (Al, atomic mass = 27 amu). Density of aluminum is ρ = 2.7 gm/cm 3 . How many Al atoms are there in 1 cc of Al? Since aluminum has an atomic mass of 27, that means that 1 mole of Al atoms has a mass of 27 grams, and one mole corresponds to 6.0 x 10 23 atoms. One cm 3 has a mass of 2.7 gms, which is 0.10 moles, or N=6.02 x 10 22 atoms.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern