Mechanical Waves & Sound Chapter 17 Mechanical Waves & Sound
How does a disturbance produce waves? Procedure Fill a clear plastic container with water. Observe the surface of the water by looking down at an angle to the container. Use the pipet to release a drop of water from a height of 3 cm above the surface of the water. Repeat Step 2 with a drop released from each of these heights: 10, 20, 50, 60, 70, 90 cm. Create a table to record your observations after each drop. These observations will be QUALITATIVE (or descriptive, and not mumeric)
Analysis Questions Which drop produced the highest wave? Write a general statement (or conclusion) about how the distance a drop falls affects the wave produced in the container. Using your knowledge of energy, conservation of energy, and energy transfer, explain why the distance a drop falls affects the height of the wave produced. Thoroughly explain your answer.
Mechanical Waves 17.1 Notes
Inquiry Activity How does a disturbance produce waves? P 499 Complete activity, answer questions as a group Submit one paper per group with all observations recorded and questions answered!
What are mechanical waves? A disturbance in matter that carries energy from one place to another Require a medium (or matter) in order to carry energy All waves carry energy!
What is a Medium? The material through which a wave travels Can be a solid, a liquid or a gas Space is NOT a medium Why?
How are mechanical waves created? A source of energy causes a vibration to travel through a medium
Types of Mechanical Waves Transverse Longitudinal (Compressional) Medium moves perpendicularly (or at right angles to the direction the wave travels) Medium moves parallel to the direction the wave travels
Transverse Waves Demos Rope (with ribbon attached) Student line (arms over shoulders)
Parts of a Transverse Wave Crest Trough Highest point of the wave Lowest point of the wave
Compressional Wave Demos Slinkys! Hip Bump
Parts of a Compressional Wave Rarefaction Area where the particles in a medium are spaced close together An area where the particles in a medium are spread out
Waves transfer ENERGY! Waves DO NOT transfer MATTER Waves ONLY transfer ENERGY Example: THE HUMAN WAVE
Surface Waves A wave that travels along a surface that separates two media (or two types of matter) An object resting on a surface wave will move up and down, and back and forth These two motions result in a circular motion for the object
Wave Animation http://njscuba.net/biology/misc_waves_w eather.html
Breaking Waves
Exit Exercise With your group, make a Venn Diagram that compares and contrast Transverse and Compressional Waves.
Properties of Mechanical Waves 17.2
Periodic Motion Any motion that repeats at regular time intervals The time required for one cycle, a complete motion that returns to its starting point
Wavelength Distance between a point on one wave and the same point on the next cycle of the wave Between adjacent Crests (or troughs), or compressions (or rarefactions)
One complete wave cycle One Wavelength
Frequency A periodic motion has a frequency Frequency The number of complete cycles in a given time For waves, this is the number of wave cycles that pass a point in a given time Measured in cycles per second, or Hertz (Hz)
Frequency & Wavelength As frequency increases, what happens to wavelength? Use the slinky at your table to determine the answer to this question, then respond using Socrative HINT: You can make either TRANSVERSE, or COMPRESSIONAL waves with your slinky
Frequency Formula Frequency = 1 *Remember, period is the amount of time it takes for a wave to complete one full cycle period
Socrative Graph #1
Socrative Graph #2 t in seconds
Socrative Questions… Two calculating frequency/ period questions
Surfing Science of Surf - Episode 1
Wave Speed REMEMBER Think of one wavelength as DISTANCE v = d/t Think of one wavelength as DISTANCE Think of period as TIME Wave Speed = wavelength / period OR Wave Speed = wavelength x frequency
Wave Speed Example One end of a rope is vibrated to produce a wave with a wavelength of 0.25 meters. The frequency of the wave is 3.0 Hertz. What is the speed of the wave? FORMULA Speed = Wavelength x Frequency
Socrative Practice Wave Speed Questions
Amplitude The maximum displacement of the medium from its rest position The more energy a wave has, the greater its amplitude
Behavior of Waves 17.3
Reflection Occurs when a wave bounces off a surface that it cannot pass through Does not change wave speed or frequency, but does change wave direction
Refraction Bending of a wave as it enters a new medium Occurs because one side of the wave moves more slowly than the other side
Refraction Example Pencil in water demonstration
Diffraction Bending of a wave as it moves around an obstacle or passes through a narrow opening A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle
Diffraction Animation Human moving with arms out http://www.acoustics.salford.ac.uk/fescho ols/waves/diffract3.htm
Interference Occurs when two or more waves overlap and combine together In interference, waves DO NOT bounce off one another, but rather move PAST each other
Types of Interference Constructive Destructive Occurs when two or more waves combine to produce a wave with a larger displacement This occurs when two crests meet, or when two troughs meet Wave amplitudes are added together, producing a larger wave during the time the waves overlap Occurs when 2 or more waves combine to produce a wave with a smaller displacement This occurs when a crest meets a trough Produces a waves with reduced amplitude
Wave Superposition When two waves interfere, the resulting displacement of the medium at any location is the sum of the displacements of the individual waves at that same location.
Animations Constructive Interference Destructive Interference
Standing Waves A wave that appears to stay in one place and does not appear to move through the medium Only certain points on the wave are stationary, not the entire wave Happens only at certain frequencies
Standing Waves Nodes Antinodes A point on a standing wave that has no displacement from the rest position Complete destructive interference between incoming and reflected waves A point where a crest or a trough appears midway between 2 nodes
Animation Standing Waves Rope/Slinky Example
Chapter 1 Midterm Review You water three sunflower plants with salt water. Each plant receives a different concentration of salt solutions. A fourth plant receives pure water. After a two week period, the height is measured. Identify the independent variable and the dependent variable in the experiment above.
Chapter 1 Review #2 One tank of gold fish is fed the normal amount of food once a day, a second tank is fed twice a day, and a third tank four times a day during a six week study. The fish’s weight is recorded daily Identify the independent variable and the dependent variable in the experiment above.
17.4 Sound & Hearing
Sound Waves Longitudinal (or Compressional) Waves Have compressions & rarefactions Cause matter to vibrate in a direction that is parallel to the direction the wave is moving
Sound Speed In dry air at 20 degrees Celsius, the speed of sound is 342 m/s Can you think of an example when you’ve experienced a sound delay? In general, sound travels fastest in solids and slowest in gases Why?
Sound Intensity The amount of energy that is transported past a given area of the medium per unit of time Sound intensity refers to how much energy the sound waves is transporting Can be measured in decibels (dB)
Sound Loudness Subjective human response to sound Depends on sound intensity
Sound Frequency Depends on how fast a sound is vibrating Most people hear sounds between 2o Hz and 20,000 Hz
Infrasound Ultrasound Infra means “below” Sound frequencies that are below what humans can hear Ultra means “above” Sound frequencies that are above what humans can hear Used in sonar and ultrasound technologies
Upper-range Frequencies http://www.audiocheck.net/audiotests_fr equencychecklow.php http://www.audiocheck.net/audiotests_fr equencycheckhigh.php
Ultrasound Sounds are bounced off parts of the body and then the reflections are used to create an image of the body part
Sonar Stands for sound navigation and ranging Sounds are bounced off an object and then the time that the sound waves takes to return to the object is measured Uses echoes
Echo Echoes occur when sound waves reflect off of objects they cannot pass through Echolocation
Doppler Effect Occurs when a source that is producing waves (like an ambulance’s siren produces sound waves) is moving with respect to any observers (like a person on the side walk watching an ambulance drive by) There is an apparent upward shift in wave frequency for observers when the sound source is moving towards them, and an apparent downward shift in frequency for observers when the sound source is moving away from them
Doppler Effect (Continued) The Doppler effect can be observed for any type of wave - water wave, sound wave, light wave, etc.
Doppler Effect Big Band Theory Clip
How We Hear Step 1: The outer ear collects sound (acoustic) energy and directs it through the ear canal to the eardrum Step 2: The incoming waves of sound energy cause the eardrum to vibrate, Step 3: The vibration of the eardrum causes three smaller bones (known as the hammer, anvil and stirrup) to vibrate as well Step 4: Sound energy is transferred to the middle ear, which amplifies the sound Step 5: Sound travels through the inner ear, eventually causing thousands of tiny sensory hair cells to vibrate Step 6: The motion of the cells triggers chemical-electrical signals that are transmitted through to the brain along the auditory nerve pathway. The brain can then translate the impulses of energy into recognizable sound patterns.