1. Properties of sound Sound is a longitudinal wave
Longitudinal waves travel at different speeds depending on the medium 25oC 346m/s, water 1490 m/s)
Denser the medium, the faster it travels, energy can transfer faster through molecules closer together.
Loudness of a sound
depends on intensity (the amplitude of the wave. Higher amplitude … louder sound)
Measured in deciBels (dB), talking is about 50 dB over 120 dB is painful.

2. Loudness/intensity

3. Properties of sound
Pitch (high or low) is directly related to frequency. Higher frequency = higher pitch
(Also related to wavelength, indirectly. Bigger wavelength = lower pitch)
Humans hear between 20 Hz and 20,000 Hz. Below that range is infrasound, above is ultrasound.

4. Musical Instruments Rely on standing waves to make sound
Only certain wavelengths are made by instruments, depending on the size of the instrument
Fundamental frequency: the lowest
frequency standing wave made by the instrument.

5. Stringed Instruments
The wavelength of the fundamental frequency is twice the length of string.
Changing the size of the string changes the wavelength and the frequency.
Changing the tension on the string changes the medium (density) and the wave speed

6. Wind/Brass Instruments
Change size of wave by opening closing holes, changes size of tube that standing wave is made in.
In an tube open at both ends, you get ½ the wavelength, so multiply by 2 to find the wavelength for the fundamental frequency
In a tube closed at one end, you get ¼ the wavelength, so multiply by 4 to find the wavelength for the fundamental frequency

7. Musical Instruments Strings make ½ wave, so mult. by 2.
Open tubes make ½ wave so mult. by 2
Closed tubes make ¼ wave so mult. by 4.

8. Resonance and Harmonics
Vibrations can cause other parts of the instrument and other objects to vibrate … called resonance.
The other standing waves created are called harmonics.
That’s why everyone’s voice sounds different and why instruments sound different when they play the same note. The have the same fundamental frequency (note), but different harmonics because of resonance
Waves interfere, called beats

9. How we hear
Outer ear focuses waves, passes them to ear drum (middle ear) which passes them to three bones (hammer, anvil, stirrup) to the cochlea (inner ear) which resonates at certain frequencies.
Hair cells pick that up and transmit to brain.

10. Ultrasound and Sonar
Use speed of sound in medium and time to figure out how far away something is (e.g. bottom of ocean floor)
Ultrasound...frequencies beyond our hearing used in medicine (babies).

11.
Good vid about fund freq, harmonics

12. Light: Waves and Particles
Like a wave … light shows interference, can reflect, refract, diffract, make standing waves, but does not require a medium
Like a particle, light can move electrons, be pulled by gravity
So light is described as having a dual nature
Comes in “packets” called photons (more like bundles of energy)
Amount of energy directly proportional to frequency. Higher freq. = more energy.
Indirectly proportional to wavelength. Bigger wave = less energy
Speed of light 3 x 108 m/s in vacuum
Speed changes for medium, but not significantly

13. Electromagnetic spectrum
all possible kinds of light, classified according to frequency and wavelength
Radio/TV Waves …lowest energy, used in communication
Microwaves…used in cooking and communication
Infrared Waves… felt as warmth
Visible light…we can see ROYGBIV
Ultraviolet waves…cause sunburn
X Rays… used in medicine
Gamma Rays… used in medicine
Stars, like the sun, give off all of these forms of energy

14. Light Rays use lines called rays to see where light goes
rough surfaces reflect the rays in all directions
smooth surfaces reflect the light in one direction
the angle light rays come in at equals the angle it’s reflected at.
Angle of incidence equal the angle of reflection (Law of Reflection)
Angles are measured between the ray and an imaginary line perpendicular to the surface called the normal.

15. Mirrors
Plane (flat) mirrors form virtual images inside of the mirror. Virtual images are from where light appears to come from, not the actual path.
Curved mirrors distort the image, but make real images. Real images form when light rays come together at a certain point

16. Color Light hits objects.
Many wavelengths are absorbed by the object and not seen by you.
Wavelengths that are reflected are seen by you as color.
Technically, you don’t see something, you see light bouncing off of something.
Colors can add together to make new colors (e.g. light. White light = all colors of light, black = absence of light)
Colors can subtract to make new colors (e.g. pigments, black paint = all colors of paint, white paint = absence of color)

17. Refraction
Light bends as it goes from one substance (medium) to another because it changes speed
Compare the bend to the normal, just like reflection
Light bends towards the normal when it enters a denser medium and slows down
Light bends away from the normal when it enters a less dense medium and speeds up

18. Lenses
Mirrors and lenses can be curved out (convex) or can curve in (concave … like a cave).

19. Light Rays
There’s an angle called the critical angle, where light will not go back out of something and just keeps bouncing back around inside.
Diamonds are cut like this to keep the light from leaving and fiber optic cables are made so that light does not escape.