1. Interactions of Waves
Chapter 11.3

2. Review: Types of Waves
Longitudinal waves - Movement of the particles are parallel to the motion of the energy.
Transverse waves - movement of the particles are at right angles (perpendicular) to the motion of the energy.
Surface waves - particles travel in a circular motion
Standing waves - a vibration of a system in which some particular points remain fixed while others between them vibrate with the maximum amplitude.
Standing Wave - a vibration of a system in which some particular points remain fixed while others between them vibrate with the maximum amplitude.

3. Reflection
Reflection occurs when an object or a wave hits a surface through which it cannot pass, and it bounces back
Examples:
Shouting in an empty gym
Looking in a mirror
The law of reflection: the angle of incidence equals the angle of reflection

4. The Law of Reflection
Angle of reflection= Angle of incidence

5. Free end and Fixed end reflection
Free end – wave goes in on top and out on top
Fixed end – wave goes in on top and out on bottom

6. Refraction
Bending occurs because the two sides of the wave are traveling at different speeds
Examples:
Seeing a rainbow
Trying to grab an object underwater
The bending of waves due to changes in speed when it enters a new medium is called refraction
Refraction occurs when a wave enters a new medium at angle, one side of the wave changes speed before the other side, causing the wave to bend

7. What are the two mediums the straw has entered?

8. Diffraction
Diffraction occurs when a wave bends around a barrier or passes through an opening in a barrier, it bends and spreads out

9. Interference Two waves can overlap when they meet
Interference is the interaction between waves when they meet
There are two types of Interference
1. Constructive Interference
2. Destructive Interference

10. Constructive Interference
Constructive Interference occurs when waves combine to make a wave with a larger amplitude
When crests from each wave meet, constructive interference makes a higher crest in the area of overlap
The amplitude of this crest is the sum of the amplitude of the two original crests
After the waves pass through each other they continue on as if they had never met

11. Destructive Interference
Destructive Interference occurs when two waves combine to make a wave with a smaller amplitude
Can be thought of as subtracting energies
Destructive interference occurs when the crest of one wave overlaps the trough of another wave
If the crest has a larger amplitude than the trough, the crest wins and part of it remains
If the original trough has the larger amplitude the result is a trough
If the original waves have equal amplitudes then the crest and trough completely cancel out

13. Nodes and Antinodes
Nodes are points of zero amplitude produced by destructive interference of standing waves
Nodes are always evenly spaced along a wave
Antinodes are points of maximum amplitude on a standing wave created by constructive interference
Antinodes are also the points of maximum energy on the wave
Antinodes occur halfway between nodes

14. Resonance
Most objects have at least one natural frequency of vibration
If a nearby object vibrates at the same frequency it can cause resonance
Resonance is an increase in the amplitude of a vibration that occurs when external vibrations match an object’s natural frequency
Resonance can be useful
Example: musical instruments use resonance to produce stronger, clearer sounds
Resonance can be harmful
Earthquakes (Mexico City Earthquake of 1985)