1. DO NOW QUESTION 4/30/15
How do noise canceling headphones work? Answer this on the Do Now answer line in your notes.
3/30 – updated as key

2. Noise canceling headphones
Specialized headphones can create “anti-noise.”
A microphone in the headphone samples the noise and generates anti-noise, or sound that is 180 degrees out of phase with the noise.
The anti-noise uses superposition to reduce or muffle noise.

3. Objective
SWBAT explain how interference affects the waves found in the world around them.

4. Unit 7: Vibrations, Waves & Sound Chapter 19: Waves
19.2 The Motion of Waves
19.3 Wave Interference and Energy

5. Superposition principle
Interference happens when two or more waves mix together.
When more than one wave is present, the total oscillation of any point is the sum of the oscillations from each individual wave – Superposition Principle

6. Constructive interference
Wave Pulse – short duration or single oscillation
Constructive interference happens when waves add up to make a larger amplitude.
Suppose you make two wave pulses on a stretched string.
waves meet, they combine to make a single large pulse.

8. Destructive interference
What happens when one pulse is on top of the string and the other is on the bottom?
When the pulses meet in the middle, they cancel each other out.
During destructive interference, waves add up to make a wave with smaller or zero amplitude.

10. Resonance and light
A wave has to be caught in a system with boundaries to show resonance.
A laser use mirrors to create resonance of light waves.

11. Resonance and elastic string
Resonance elastic strings is created by adding new pulses so that each adds to the reflected pulse in constructive interference.
Examples: The tides of the oceans, musical instruments, the laser, the way our ears separate sound, and even a microwave oven are all examples of waves and resonance

12. Energy is what actually moves.
Waves and energy
Energy is what actually moves.
The energy of a wave is proportional to its frequency & amplitude.

13. Waves and energy Higher frequency means higher energy.
Small amplitude means low energy
Triple frequency means triple energy

14. Waves that Shake the Ground
On January 12, 2010, a 7.0 magnitude earthquake struck the Caribbean nation of Haiti.
Its capital, Port-au-Prince, was nearly destroyed.
Many government buildings, schools, hospitals, and businesses collapsed.
The powerful earthquake was caused by waves traveling through Earth.