How Things Work / TUNE - Fall 2017

Hi there, Our final exam will be Wednesday, December 13 at 7:30 PM.  Normal class location.

The Doppler Effect http://www.lon-capa.org/~mmp/applist/doppler/d.htm http://falstad.com/mathphysics.html Run the Ripple tank applet - http://falstad.com/ripple/ The key in the Doppler effect is that motion makes the "detected" or "perceived" frequencies higher or lower. If the source is moving toward you, you detect/measure a higher frequency - this is called a BLUE SHIFT. If the source is moving away from you, you detect/measure a lower frequency - this is called a RED SHIFT. Distant galaxies in the universe are moving away from us, as determined by their red shifts. This indicates that the universe is indeed expanding (first shown by E. Hubble). The 2011 Nobel Prize in Physics went to local physicist Adam Riess (and 2 others) for the discovery of the accelerating expansion of the universe. Awesome stuff! http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/ It's worth noting that the effect also works in reverse. If yo...

Animation of sound as a mechanical wave: http://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html Music In western music, we use an "equal tempered (or well tempered) scale."  It has a few noteworthy characteristics; The octave is defined as a doubling (or halving) of a frequency. You may have seen a keyboard before.  The notes are, beginning with C (the note immediately before the pair of black keys): C C# D D# E F F# G G# A A# B C (Yes, I could also say D-flat instead of C#, but I don't have a flat symbol on the keyboard.  And I don't want to split hairs over sharps and flats - it's not that important at the moment.) There are 13 notes here, but only 12 "jumps" to go from C to the next C above it (one octave higher).  Here's the problem.  If there are 12 jumps to get to a factor of 2 (in frequency), making an octave, how do you get from one note to the next note on the piano?  (This is ca...

Try wave problems 1-5 in the first set below. And if time permits, play around with this: https://phet.colorado.edu/en/simulation/wave-on-a-string Wave problems 1 and 2, with answers Wave questions I 1.  Differentiate between mechanical and electromagnetic waves.  Give examples. 2.  Draw a wave and identify the primary parts (wavelength, crest, trough, amplitude). 3.  Find the speed of a 500 Hz wave with a wavelength of 0.25 m. 4.  What is the frequency of a wave that travels at 24 m/s, if 3 full waves fit in a 12-m space?  (Hint:  find the wavelength first.) 5.  Show how to compute the wavelength of WTMD's signal (89.7 MHz).  Note that MHz means 'million Hz."  Recall that radio waves travel at the speed of light. 6.  Middle C vibrates at 262 Hz (approximately).  Find the frequencies of the next 2 C's (1 and 2 octaves above this one). Answers: 1/2.  See notes 3.  v = f l = 500(0.25) = 125 m/s 4.  wavelength ...

Energy??? I stole my energy story from the famous American physicist Richard Feynman. Here is a version adapted from his original energy story. He used the character, "Dennis the Menace." The story below is paraphrased from the original Feynman lecture on physics (in the early 1960s). Dennis the Menace Adapted from Richard Feynman Imagine Dennis has 28 blocks, which are all the same. They are absolutely indestructible and cannot be divided into pieces. His mother puts him and his 28 blocks into a room at the beginning of the day. At the end of each day, being curious, she counts them and discovers a phenomenal law. No matter what he does with the blocks, there are always 28 remaining. This continues for some time until one day she only counts 27, but with a little searching she discovers one under a rug. She realizes she must be careful to look everywhere. One day later she can only find 26. She looks everywhere in the room, but cannot find them. Then she realises the window ...

Introduction to WAVES. So - Waves.....   We spoke about energy.  Energy can, as it turns out, travel in waves.  In fact, you can think of a wave as a traveling disturbance, capable of carrying energy with it.  For example, light "waves" can have energy - like solar energy.  Ocean waves can certainly carry energy.   There are several wave characteristics (applicable to most conventional waves) that are useful to know: amplitude  - the "height" of the wave, from equilibrium (or direction axis of travel) to maximum position above or below crest  - peak (or highest point) of a wave trough  - valley (or lowest point) of a wave wavelength (lambda - see picture 2 above)  - the length of a complete wave, measured from crest to crest or trough to trough (or distance between any two points that are in phase - see picture 2 above).  Measured in meters (or any units of length). frequency (f)  - literally, the number of complete waves per s...

A very useful concept in physics is Center of Gravity (AKA CM, Center of Mass - they are usually the same point).   Recall the demo with the mass on a stick.  Same mass, held at a further distance from the "fulcrum", is harder to support.  It twists your wrist more - it requires a greater "torque". So, what is torque? Torque - a "rotating" force T = F L For an object to be "in equilibrium," not only must the forces be balanced, but the torques must also be balanced. Consider a basic see-saw, initially balanced at the fulcrum:  See image below. You can have two people of different weight balanced, if their distances are adjusted accordingly:  the heavier person is closer to the fulcrum.   Mathematically, this requires that the torques be equal on both sides. Consider two people, 100 lb and 200 lb.  The 100 lb person is 3 feet from the fulcrum.  How far from the fulcrum must the 200 lb person sit, to maintain eq...