# Week 3

Read: and Falling Bodies and Pendular Motion (ASGv2 Chap. 4), Pendular motion and harmony (ASGv2 Chap. 5)

Key topics: Periodic motion, pendulums, sound waves, vibrating strings, frequency and pitch, consonance and dissonance, sympathetic resonance

PHY 201 lecture: Drag, nonuniform acceleration, and terminal velocity.
Quiz: Quiz covering week 2 material.

Homework:
1. Ivory Balls (Ex. 4.1)
2. Comparing pendulums (Ex. 4.2)
3. Dissonance (Ex. 5.1),
4. Suspended weight (Ex. 5.2),
5. violin strings (Ex. 5.3). Hint: you will need to look up the frequency of a G and an E note.
6. harmony essay (Ex. 5.5)
7. PHY 201 problem: Drag reduces the acceleration of a falling body because it exerts a force opposite the direction of motion of the falling body. As a ball falls through a fluid, the drag force exerted by the liquid increases until the sum of the drag and buoyancy balance the ball's weight. At this time, the ball achieves so-called "terminal velocity." (a) What is the terminal velocity of a 2mm diameter indium ball falling through liquid gallium? Hint: at terminal velocity, the acceleration is zero. Let's assume that the flow around the ball is turbulent, so that the drag force is given by D = 1/2 * (fluid density) * (cross sectional area of sphere) * (drag coefficient of sphere) * v^2. The drag coefficient of a sphere is approximately 1. (b) Now: repeat this problem for an indium ball if it is submerged in liquid mercury (instead of liquid gallium). In particular: what is its terminal velocity? Does the indium ball ascend or descend?

Lab:
Harmony (Ex. 5.6). In lab this week, we will be exploring sound using tuning forks, microphones, and logger-pro software. Be sure to include clear plots of your recordings, along with curve-fits to your data!

Strange: Galileo's finger is located in the Museo di Storia del Scienza in Florence, Italy (Hat tip to Rachel Dziekan, who kindly notified me of this link.)

Chapter 4: These 4 videos deal with the effect of drag on falling bodies.

Chapter 5: These four videos deal with Galileo's theory of sound and harmony.

Here are a couple of interesting optional videos: The first is about music (specifically Led Zeppelin); the second is a mesmerizing video about pendulums.

Physics 1