1. Types of Mechanical waves

2. Transverse waves
For transverse waves the displacement of the medium is perpendicular to the direction of propagation of the wave.
A ripple in a pond and a wave on a string are example.

3. Longitudinal Waves
In longitudinal waves the displacement of the medium is parallel to the propagation of the wave.
A wave in a "slinky" is a good visualization.
Sound is an example.

4. Surface or Elliptical waves
waves that involve a combination of both longitudinal and transverse motions
As a wave travels through the water, the particles travel in clockwise circles.

5. Universal Wave properties
We will discuss the 4 universal properties of waves

6. The 4 properties
Reflection
Refraction
Diffraction
Interference

7. Reflection Bouncing back of a wave as it strikes a boundary
A closer look

8. Refraction
The bending of a wave as it passes the boundary between two media.
Example: Pole in pool looks bent, eyeglasses.

9. Diffraction
The bending or spreading of a wave as it passes an obstruction.
Example: light go through keyhole or bending around a corner.

10. Interference
When two or more waves share the same space at the same time.
These waves both act independently on the medium
Example: two radio stations at once.

11. Constructive Interference
When two waves tend to do same thing to medium, the total effect builds up. This is know as constructive interference.

12. Destructive Interference
When two waves tend to do opposite things to medium, the total effect cancel out. This is know as destructive interference.

13. Noise Cancellation
Destructive interference, if applied correctly, can be very useful.
In an airplane, the engine noise presents a problem.
Pilots can use special headphones mounted with a microphone the headphones creates a wave that is the inverse of the wave that represents the engine noise.

14. Noise Cancellation
The wave is then played back through the headphones allowing destructive interference to produce a quieter background. Other applications for destructive interference are "quieting" cars and passenger sections in airplanes.