1. 8th Grade Physical Science
Sounds Good to Me!
8th Grade Physical Science

2. What Is Sound?
Sounds are vibrations that you can hear

3. Sound Depends On 3 things:
A vibrating source to set up the sound waves
A medium to carry the waves
A receiver to detect them

4. So Here is an old riddle:
If a tree falls in a forest and no one or no living thing hears it, does it make a sound?
Based upon what you just learned in the previous slide, discuss your answer with your neighbor .

5. Vibrations Back-and-forth movement of matter or particles of matter
Sound travels away from the vibrating object in all directions

6. Imagine ripples spreading out in circles after you toss a pebble into a pond. In a similar way, sound waves spread out from a source. The total energy of the wave however remains the same BUT….
The closer the sound wave
is to the source, the more energy
it has in a given area. This is called INTENSITY!

7. Sound Waves
Sound travels through matter as sound waves (compressional)
Particles of air are pushed together and then pulled apart
Compressions occur where particles of a medium are pushed together, and rarefactions occur where the particles are pulled back apart.

8. Volume = Amplitude Amount of sound energy reaching your ears
Depends on:
How far the vibrating object is moving as it goes back and forth
How far you are from the source of a sound
The greater the Energy, The greater the Amplitude.
Volume Control

9. Amplitude of a wave

10. Loudness
Loudness is an important property of sound. Loudness describes your perception of the energy of a sound.
Think about when your are speaking with a friend – what do you already know about loudness.
Speak softly with a neighbor about what
you know.

11. Energy of a sound source
Usually, the greater the energy used to make a sound, the louder the sound

12. If you hypothesized this guy, you are correct. But why?
The reasons include:
Heavier strings that require more energy to play.
An electric amplifier that produces a larger amplified sound wave.
Greater pressure on the eardrum due to larger compressional waves.

13. Measuring Loudness Loudness is measured in units called decibels (db).
Each 10 dB increase in loudness represents a ten times increase in the intensity of the sound

15. Human hearing (frequencies)
Humans can hear a range of frequencies from around 20 Hz to around 20,000 Hz.
Sound waves with frequencies above the normal range of hearing are called ultrasound.
Sound waves with frequencies below the normal range of hearing are called infrasound.

17. Frequency Hearing Test
click here to test
Raise you hand when you can first hear the tone.
Keep your hand up until you can no longer hear the tone.
Write down your frequency range.

18. Frequency = Pitch
How high or low a sound is, known as pitch, is related to its frequency.
High pitch = High Frequency
Low pitch = Low Frequency
Remember: The sky is high; the roots are low
Pitch depends on how fast the source of the sound is vibrating
To change the pitch:
Change the length of the material vibrating
Change the thickness of the material vibrating

19. High & Low Frequency Waves

20. The Doppler Effect
The Doppler effect is the apparent change in the frequency of a sound caused by the motion of either the listener or the source of the sound.
Click for example

22. Sounds From Moving Sources
If the source is moving as fast or faster than the speed of sound, the sound waves pile up into a shock wave called a sonic boom.
A sonic boom sounds very much like the pressure wave from an explosion

23. Reflection vs. Absorption
Sound waves can be reflected, absorbed, refracted or diffracted.
Sound waves reflect straight from a smooth, flat surface and produce a clear echo. Several echos in a row are called reverberation.
Sound waves that strike a rough, uneven surface do not produce an echo but rather the surface will scatter or absorb the sound.

24. Refraction Vs. Diffraction
Sound waves will change speeds when entering and exiting different mediums which will cause them to refract and distort.
Unlike light which travels in a straight line, sound travels in all directions and spreads out as it travels. As a result of this diffraction of sound waves, we have the ability to hear around corners and behind us.

25. Sound Travels at Different Speeds Through Different Materials
Feet per second

26. What makes Music…Music?
Music is a group of sounds that have been deliberately produced to make a regular pattern of pitches, or notes.
Every object will vibrate at a certain frequency, known as its natural frequency.
Musical instruments are usually made from materials that have a low natural frequency like wood.
This allows the instrument to vibrate freely and project the sound of the instrument. This vibration is known as resonance.

27. Natural Frequency Examples
shatter a glass w/ your voice
Tacoma Washington Bridge

28. Stop That Noise!!!
What is noise? How do you know if you are making it if you don’t know what it really is?
Noises are sounds that are disorganized and have no regular patterns or pitches.
However, what one might consider to be noise, another might consider to be music. After all, the art is in the ear of the listener!

29. Instrument Project X-Tra Credit
Should be:
Well designed
Simple
Functional
Attractive
Creative
You must be able to:
Produce Sound
Change Pitch
Change Volume
Play a simple recognizable tune