1. 7th grade Notes Week 17-Monday
Waves Intro

3. Waves Intro: what it is…
C-notes
A wave is a disturbance caused by a force
Example: you drop a pebble in water, a wave is formed

4. Waves: What do they do? C-notes Waves transfer ENERGY
The molecules of the MEDIUM do NOT
Move to another place…

5. Waves Intro: Causes & Examples C-notes
Water waves…caused by wind (some by Earthquakes- tsunami)
Ground shakes because pressure is released (EARTHQUAKE)
You hit something it vibrates making a sound. Sound moves in waves

6. There are two types of waves: Mechanical and Electromagnetic
Waves Intro: Types of waves
C-notes
There are two types of waves:
Mechanical and Electromagnetic

7. Waves Intro: Mechanical
C-notes
Mechanical waves are waves that move in MATTER.
If there is no “MATTER”; there is no movement
MEDIUM- is any type of matter that mechanical waves move in

8. Mechanical Wave: An example
C-notes
Sound is an example of a mechanical wave.
Sound is produced by vibrations
The energy from the vibration moves in waves
Sound can ONLY travel if there is a medium

9. Waves Intro: Electromagnetic
C-notes
Electromagnetic waves can move through “empty” space.
A place with little or no molecules is called a vacuum

10. Parts of a Transverse wave
C-notes
Crest- highest point of the wave
REST LINE
If there were no energy…
Trough (troff)- lowest point of the wave

11. Types of mechanical waves
C-notes
Transverse waves are waves in which the movement of the vibrating particles is perpendicular to the direction of the wave.
Example:
Water wave

12. Types of mechanical waves
C-notes
Longitudinal waves are waves in which the movement of the vibrating particles is parallel to the direction of the wave.
Example: sound wave

13. Properties of (ALL) Waves
Frequency:
How many crests pass in a second
Amplitude:
Measure from rest line to crest
Wavelength:
Measure from one crest to the next
Properties of (ALL) Waves

14. The more amplitude the more energy.
The energy of the wave.
The more amplitude the more energy.
The number of vibrations (waves) each second.
Unit used: hertz
The distance between one crest and another

15. Sound energy is the energy of vibration
C-notes
Sound energy is the energy of vibration
Sound produces an mechanical wave- it needs a medium to move in

16. Sound waves are LONGITUDINAL waves
Sound Energy
C-notes
Sound waves are LONGITUDINAL waves
Another name for longitudinal waves is a COMPRESSION wave

17. Sound Energy
C-notes
Sound waves have the same properties as waves (amplitude, wavelength, frequency)
However there are two “parts” to a COMPRESSION wave

18. Sound Energy
C-notes
Compression- where molecules of medium and pressed together
Rarefaction- where molecules of a medium spread apart

19. Hearing and Wave properties
C-notes
Our ears can sense the amplitude of a sound wave
The more energy, the more amplitude.

20. Hearing and Wave properties
C-notes
The greater amplitude is sensed as INTENSITY (LOUDNESS)
The sound intensity is measured with a unit called decibel

21. Hearing and Wave properties
C-notes
Our ears can sense frequency of the vibration
The more vibrations, the higher the frequency. This is a high pitch sound

22. Hearing and Wave properties
C-notes
Our ears can sense frequency of the vibration
The more vibrations, the higher the frequency. This is a high pitch sound

23. Hearing and Wave properties
C-notes
Frequency is measured in a unit called HERTZ (Hz). These are vibrations per second
We can “hear” 20 hertz to 20,000 hertz