1. Chapter 12 Section 4
Wave Interactions

2. Wave Interference
It’s impossible for two material objects to occupy the same space at the same time.
Waves on the other hand are able to occupy the same space at the same time.

3. Superposition
Superposition – The ability for a wave to occupy the same space at the same time.
Superposition is possible for all forms of waves:
Sound
Water
Light

4. Constructive Interference
Constructive Interference – Interference in which individual displacements on the same side of the equilibrium position are added together to form a resultant wave.
When the two waves meet, they form a larger amplitude wave. Once they pass through one another, they return to their original amplitude.

5. Constructive Interference

6. Destructive Interference
Destructive Interference – Interference in which individual displacements on opposite sides of the equilibrium position are added together to form a resultant wave.
When the two waves meet, they form a smaller amplitude wave or even cancel out. Once they pass through one another, they return to their original amplitude.

7. Destructive Interference

8. Constructive vs. Destructive Interference
Superposition of Waves Animation

9. Interferences In Waves
The method of summing the displacements of waves is known as the Superposition Principle.
This principle only holds true for small waves
Superposition principle is valid for both transverse and longitudinal waves.

10. Wave Reflection
At a free boundary, waves are reflected back to the source and the amplitude is unchanged.
At a fixed boundary, waves are reflected and inverted back to the source with the amplitude unchanged but upside down.

11. Reflection Diagram

12. Standing Waves
Standing Wave – Wave pattern that results when two waves of the same frequency, wavelength, and amplitude travel in opposite directions and interfere.
Node – Point in a standing wave that always undergoes complete destructive interference and therefore is stationary.
Antinode – Point in a standing wave, halfway between two nodes, at which the largest amplitude occurs.

13. Standing Waves Explained
Standing Waves are formed when both ends of a string, rope or spring, are fixed at both ends and the waves reflect on both ends.
The incident and reflected waves combine according to superposition principle.
As long as the frequency of the waves remains constant a standing wave will form.

14. Standing Wave Diagram

15. Doppler Effect?
Your standing on a street and some driving by honks the horn, you will notice the pitch of the horn change.
The pitch gets higher as the car comes closer.
Once the car passes, the pitch will drop.
The pitch depends on the frequency of the wave.

16. Doppler Effect Diagram

17. Doppler Effect Animation

18. Doppler Effect of Light
Doppler effect can happen for light waves as well.

19. Doppler Effect
Doppler Effect – Frequency shift that is the result of relative motion between the course and an observer.
When an object moves, it effects the frequency of the wave that is being emitted.
Doppler effect occurs for all types of waves.