1. Waves & Energy
Powerpoint Templates

2. Waves are a Form of Energy
• What do we know about energy?
– It is the ability to do work (make changes)
– It cannot be created or destroyed
– It can be transferred between objects
• Waves are vibrations that transfer energy
from place to place
– back-and-forth movements
• push-and-pull forces
• "disturbance" or oscillation
– spread in all directions
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3. Mechanical vs. Electromagnetic
• Mechanical Waves
– travel ONLY through matter
• energy is transferred from place to place
• matter moves but returns to original location
– travel through a solid, liquid or gas medium
• type of medium affects how quickly the wave can travel
– cannot travel through space where there is no matter
– Examples:
• sound waves
• ocean waves
• seismic waves
Powerpoint Templates

4. Mechanical vs. Electromagnetic
• Electromagnetic Waves
– CAN travel through a vacuum (lack of matter, even air molecules)
– can also travel through matter (solid/liquid/gas)
• Electromagnetic Spectrum
– radio waves, microwaves, infrared waves
– X rays, light, heat
• we'll look at these
in a couple weeks
Powerpoint Templates

5. Anatomy of a Wave
• Crest: highest point
on a wave
• Trough: lowest point Amplitude
on a wave Node
• Node: midway point
between crest & trough
• Wavelength: distance between crests (λ in meters)
• Amplitude: height of the wave (A) - (MIDDLE to crest)
– shows how much energy a wave carries
• Frequency: how many waves hit a certain point every
second (Hz = Hertz = waves per second)
Powerpoint Templates

6. Transverse Waves
• A transverse wave has vibrations (oscillations)
perpendicular to the direction the wave travels
– propagation (direction wave travels) is to the right
– oscillation is up and down
• May be mechanical or electromagnetic
– Examples: ocean waves, X-rays or light
If the graph show
here represented
1 second of time,
what would the
Oscillation
frequency be?
Answer: 2.5 Hz
Powerpoint Templates

7. Longitudinal Waves
• A longitudinal wave oscillates parallel to the
direction the wave travels
– propagation is to the right
– oscillation is left and right
• All longitudinal waves are mechanical
– Examples: sound waves, seismic waves
• Also called compressional waves
If the graph show
here represented
1 second of time,
what would the
frequency be?
Answer: 3 Hz
Powerpoint Templates Oscillation

8. Longitudinal Waves
• In longitudinal waves, matter is compressed (squeezed
or pushed together) to form the wave motion.
– point of greatest compression = "crest"
– point coils are most spread out (rarefaction) = "trough"
• Amplitude is displayed in how tightly the medium is
squeezed together in its regions of compression.
– more tightly compressed coils Templatesamplitude (more energy)
Powerpoint = higher

9. Sound Waves
• When you hear a sound, it is caused by air
molecules being compressed in waves.
Powerpoint Templates

10. Transverse & Longitudinal
Waves
Rarefaction
Comparison
Powerpoint Templates

11. Powerpoint Templates

12. Wavelength & Frequency
• Wavelength, frequency and wave speed can be
described mathematically by the following
equation:
wave speed (v) = frequency (f) x wavelength (λ)
f = v
λ
Powerpoint Templates

13. A, f & λ Relationships
• Beads on a String Demo
f= v
λ
• As frequency increases, the wavelength decreases.
– f and λ are inversely proportional
Powerpoint Templates

14. Practice Problem
• A marine weather station detects waves which are 9.28 meters
apart and 1.65 meters high and travel a distance of 50 meters in
21.8 seconds. Determine the speed, amplitude and frequency of
these waves.
Speed
Speed (v) = distance/time = 50m ÷ 21.8s = 2.3m/s
Amplitude
Amplitude (A) = ½ wave height = .5 x 1.65m = .825m
Frequency
Frequency (f) = v/λ = 2.3m/s ÷ 9.28m = .25 Hz
Powerpoint Templates

15. Frequency & Period
• The period (T) of a wave is the time it
takes for one wave to pass a certain point
(or the time between each wave).
• If this graph shows 1 Period (T)
second of time, the
frequency (f) is 3Hz.
• 3 waves per second
means the period (time
between each wave) is T=1
1/3 of a second. f
Powerpoint Templates

16. Practice Problem
• Strong winds can apply a significant enough force to tall
skyscrapers to set them into a back-and-forth motion. The
amplitudes of these motions are greater at the higher floors and
barely observable for the lower floors. It is said that one can even
observe the swaying motion of the Sears Tower in Chicago on a
windy day.
– As the Sears Tower vibrates back and forth, it makes about 8.6
vibrations in 60 seconds. Determine the frequency and the
period of vibration of the Sears Tower.
f = waves per second = ?/s
T=1
f
f = 8.6/60s = .143 = .14 Hz
period = 1/f = 1 = 6.98s (about 7 seconds)
.14
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