1. Wave Interactions

2. Why Do Waves Interact? Reflection Refraction Diffraction Interference
Waves don’t just transfer energy from one location to another along a simple path.
All of the time, waves carrying energy interact with other objects and other waves on their way to their final destination.
There are several different ways that waves can interact, including:
Reflection
Refraction
Diffraction
Interference

3. Why Do Waves Interact? Reflection Refraction Diffraction Interference
Waves don’t just transfer energy from one location to another along a simple path.
All of the time, waves carrying energy interact with other objects and other waves on their way to their final destination.
There are several different ways that waves can interact, including:
Reflection
Refraction
Diffraction
Interference

4. Reflection
Reflection – when a wave hits a surface that it cannot pass through and bounces back
-- this is how echoes form
-- also when you splash waves off of the side of a bathtub or swimming pool
The way that a wave reflects off of a surface depends on the direction with which the wave hits the surface

5. Parts of a Reflected Wave
When a wave reflects off of a surface it creates two angles, an angle of incidence and an angle of reflection
Angle of Incidence – angle formed between incoming (incident) wave and a line perpendicular to reflection surface
Angle of Reflection – angle formed between reflected wave and the same line perpendicular to reflection surface

6. Refraction Refraction – the bending of a wave as it changes mediums
Why does refraction occur?
-- the speed of the wave is entirely determined by the medium through which it passes
-- as a wave changes mediums (say, from air to water), the wave changes speed, and can bend
-- the wave will only bend if one side of the wave enters the new medium first (usually, this happens when waves travel at an angle)
Example:
-- this is why objects underwater look distorted because light waves change speeds

7. Images of Refraction

8. Diffraction Diffraction
Diffraction – the bending of waves around an obstacle in its path
- happens when the object is not large enough to reflect the entire wave
- after the wave bends, it tends to spread back out
Diffraction can occur through a notch or around a bend
- To see diffraction in action click below!
Diffraction

9. Interference
Interference happens when two or more waves come in contact and interact with one another.
Depending on the way that the waves interact, the interference pattern can be constructive, destructive, or a combination of both constructive and destructive interference

10. Constructive Interference
Constructive Interference – happens when two difference waves arrive “in phase”, so that crests match crests and troughs match troughs
-- amplitudes are combined to be greater than the original amplitude

11. Destructive Interference
Destructive Interference – occurs when waves arrive completely “out of phase” with each other so that crests match up with troughs
-- waves cancel each other out

12. Partial Interference
Most waves interact so that they are partially out of phase
-- some crests match with crests, but other crests match with troughs
-- creates pockets of both constructive and destructive interference
-- happens because waves travel at different speeds in different mediums

13. To see more interference patterns, check out this applet:

14. Standing Waves
Once interacting waves have passed one another, interference stops
Some waves, like two waves on the same rope, can pass each other in such a way that the interference pattern remains constant, creating what is known as a standing wave.
Standing Wave – a wave that appears to be not moving, or standing still, because of the interference patterns of two opposite-moving waves

15. Parts of a Standing Wave
There are two parts to all standing waves – nodes and antinodes
Nodes – where destructive interference occurs and amplitude is at zero
Antinodes – the crests and troughs of the standing wave where maximum constructive interference occurs

16. To see a standing wave in action, click on the link below:

17. Resonance
The molecules in all objects naturally vibrate at a specific frequency
Sometimes, waves with the same frequency will vibrate the object, causing the amplitude to increase significantly. This is called resonance.
Resonance can be good or bad:
-- in music, it makes sound more pleasing
-- can also cause inflexible objects to shatter if resonance becomes too large
Ceann