New Standard • SPS9: Students will investigate the
properties of waves. – a. Recognize that all waves transfer energy.
b. Relate frequency and wavelength to the energy of different types of electromagnetic waves and mechanical waves. c. Compare and contrast the characteristics of electromagnetic and mechanical (sound) waves. d. Investigate the phenomena of reflection, refraction, interference, and diffraction. e. Relate the speed of sound to different mediums. f. Explain the Doppler Effect in terms of everyday interactions.
17.1:
Mechanical
Waves
What is a wave? • When matter is disturbed, energy comes
from the disturbance. This energy is in the form of a wave.
• A disturbance such as a pulse or shock produces a wave. – These disturbances are many times repeated or
periodic, such as a guitar string being struck. This makes the wave continuous
ALL WAVES TRANSPORT
ENERGY!
Mechanical Waves
Disturbance in matter that
carries energy from one place
to another
Mechanical Waves
• Created when a source of energy causes a vibration to travel through a medium.
• Requires a medium to travel through.
• Solids, liquids, and gases
• Classified by the WAY they move through a medium.
3 Main Types of Mechanical Waves
•Transverse waves
•Longitudinal waves
•Surface waves
Transverse Waves • Wave that causes the medium to vibrate at right angles to the direction in which the wave travels.
• The wave carries energy from left to right
• The highest point of the wave is the crest.
• The lowest point of the wave is the trough.
Transverse Waves Direction of wave
Crest
Rest position
Trough
Direction of vibration
Examples of Transverse Waves
• Ripples created when rock is thrown into water
• Rope tied to a tree
• Motion of a plucked guitar string
• Light waves…also called electromagnetic waves
• Secondary earthquake waves
Secondary Earthquake Waves
• Come after Primary Wave
• Cause the ground to roll
Longitudinal Waves • Waves in which the vibration of the medium is
parallel to the direction the wave travels.
• An area where the particles in a medium are spaced close together is called a compression.
• An area where the particles in a medium are spread out is called a rarefaction.
Longitudinal Waves
Examples of Longitudinal Waves
• Sound
• Primary earthquake waves
• Shock waves from an explosion
Surface Waves • Wave that travels along a
surface separating two media.
• Particles of the medium undergo a circular motion.
• Ocean waves are the most familiar kind of surface waves.
17.2: Properties
of Mechanical
Waves
Period • The time required for one complete
cycle to pass a particular point cycle is called the period.
1 Period
Frequency • The number of complete cycles in a given
time.
• Measured in cycles per second, or hertz (Hz).
•One hertz equals one wave cycle per second.
Frequency & Energy
Frequency & Energy have a Direct Relationship
High frequency=high energy
Low frequency=low energy
Wavelength • The distance between a point on one
wave and the same point on the next cycle of the wave.
–One wave cycle is equal to one wavelength.
Measuring Wavelength
Long wavelength Short wavelength
For a transverse wave, wavelength is measured between adjacent crests or between adjacent
troughs.
Measuring Wavelength
• For a longitudinal wave, wavelength is the distance between adjacent compressions or rarefactions.
Frequency & Wavelength
• Inverse relationship – Increasing the frequency of a wave decreases its
wavelength.
– Low frequency=Long wavelength
– High frequency=Short wavelength
Wave Speed • Formula:
Speed=Wavelength X Frequency • Units=meters per second
• Speed of a wave can change if it enters a new medium but for most waves the speed will remain constant.
Amplitude • The maximum displacement of the medium
from its rest position. – How high the wave rises.
– Intensity.
• Increase in amplitude means the wave carries more energy. – This is due to the fact that it takes more energy to
produce a larger wave.
– The more energy the wave has, the more the medium will be compressed or displaced.
Measuring Amplitude
Amplitude • Louder sounds have a greater amplitude.
• Brighter lights have a greater amplitude.
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