This is lecture 5, Wave interference, standing waves, resonance, intro to sound waves. For Conceptual Physics course, Physics 102, at University of New Mexico. Koch's section.

3. Some good student answers “Some!”—many good ones not here, sorry Lisa: "The way I understand conservation of energy is that it can not be created or destroyed, it can be transformed into one form or another, but the amount of energy does not change. So, I would say that both balls have the same amount of speed when they hit the ground regardless of being thrown upward or downward because the amount of energy does not change regardless of the directions the balls are thrown. " Ritchy : "... and will hit the ground at the same velocity. Of course if the second ball is made from enriched uranium.... " John : "...After passing this point, ball # 2 will fall with the same speed as # 1 did and will follow the same trajectory, and therefore will hit the ground with the same speed ball # 1 did. " Adrian: “…it would regain the speed it had traveling upwards because it would not have transfered that energy elsewhere." Brian : "The law of the Conservation of Energy states that energy can be transformed but never created or destroyed. Because both balls are being thrown at the same speed in the same gravitational zone both balls have the same amount of energy and therefore will hit the ground at the same speed... Reuben: So while they will hit the ground at different times they will be at the same speed when they hit. " Audrey : "..The same amount of energy put in will be the same till it hits the ground because nothing is getting in its way. This is a trick question. " Aubrey: "Think of how ball #2 would look on a graph. It's velocity would slightly decrease until it reached the top of its path, and then increase on its way down until it hit the ground. Its velocity would be mirrored, then, the same on the way up as the way down...."

4. Homework problem…conservation of energy #1 #2 20 mph Initial speed for both Same initial height Q: Which hits ground with more speed? (neglecting air resistance) You could analyze with F = ma, Equations of motion, etc. But much easier using conservation of energy!

5. Homework problem…one viewpoint #1 #2 20 mph Initial speed for both Same initial height Q: Which hits ground with more speed? (neglecting air resistance) Which one has higher initial total energy (KE + PE)? Can the ball lose total energy while in the air (without air resistance)? KE = ½ m v 2 PE = m g h So which one would have more energy when hitting ground?

6. Homework problem…another viewpoint #1 #2 20 mph Initial speed for both Q: Which hits ground with more speed? (neglecting air resistance) If energy is conserved, then what will be the speed of ball #2 when it returns to the point it started? ? mph Potential energy is the same… Given that information, which ball would hit faster? Check student answers on WebCT (tomorrow night?) Answer is: same speed Think about energy flow and conservation of energy…this plays a part in waves too. #2

7. Clicker question--wavelength Let’s discuss this one in groups

9. Reminder about amplitude and wavelength

12. I wish we could look at wave interference with a real demo! Wave table!

20. Reminder of difference between transverse and longitudinal waves Transverse Wave Longitudinal wave Imagine this is a speaker (sorry, I am missing the citations for these animated gifs)

22. Note: we ran out of time here and did not get to discuss the following slides in today’s lecture (Feb. 3, 2009)

25. 1. Yes 2. No Does the wind affect the pitch of a factory whistle you hear on a windy day?

27. Ripple tank applet for Doppler Effect http://www.falstad.com/mathphysics.html ripple Nerf Doppler Demo Possibly this applet if it works http://physics-animations.com/Physics/English/waves.htm