k-12 science, ccsd, 2006 9/11 p. 20 waves introduction notes iq: put a check mark by things that you...
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K-12 Science, CCSD, 2006
9/11 p. 20 Waves Introduction Notes
IQ: Put a check mark by things that you think involve wave action:
• Sun’s rays• Musical instruments• Earthquake• Radios• Water
K-12 Science, CCSD, 2006
Waves• A wave is any disturbance that
transmits/moves energy through matter or space through vibrations.
• A wave is energy, not matter being moved from one place to another.
K-12 Science, CCSD, 2006
Waves
• You can sometimes see a wave start.• The energy moves out in all directions
from the source.
K-12 Science, CCSD, 2006
The waves on the pond move toward the shore, but the water & the fishing lure floating on the
surface don’t move w/the wave
K-12 Science, CCSD, 2006
Waves• We draw waves to represent energy. • If you vibrate a string, you demonstrate a wave.• A vibration is a back and forth movement of an
object. video
K-12 Science, CCSD, 2006
The material a wave travels through is called a medium. Ex.
Water (liquid)
Air (gas)
Ground(Solid)
K-12 Science, CCSD, 2006
• Waves that NEED a medium to travel are called Mechanical waves. Ex. Sound, ocean waves.
• Waves that can travel without a medium are Electromagnetic waves. Ex. light, x-rays, microwaves.
EM Waves
• Require no medium to travel
• Can go through space
• Light/EM waves• How do we know EM/light
waves can go through space? (answer on pg )
Mechanical Waves
• Require a medium to travel
• Sound, slinky seismic & H2O are all examples
• Knowing this, what’s wrong/incorrect w/most SciFi movies, such as Aliens?! (answer on pg )
K-12 Science, CCSD, 2006
Types of Waves1. Transverse Waves: particles move
with an up and down motion, perpendicular to the direction of the wave. Ex. light waves.
Video
This is drawn like this:
K-12 Science, CCSD, 2006
Parts of a Transverse Wave
A = Crest: highest pt. of wave
B = Trough lowest point of wave
D = 1 full wave
= 1 wavelength
C = Amplitude: height of wave
CA
B
D
K-12 Science, CCSD, 2006
Parts of a T Wave
K-12 Science, CCSD, 2006
Types of Waves2. Longitudinal waves/compressional waves: Particles move back and forth, (parallel) in the same direction as the wave’s energy. Ex. sound waves.
K-12 Science, CCSD, 2006
Parts of a Longitudinal Wave
Compression: particles are pushed close together.
Rarefaction: particles are spread apart. Video
Video
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Water waves
Water waves have transverse and longitudinal characteristics.Energy is transferred, but the particles stay essentially in the same place
K-12 Science, CCSD, 2006
• OQ: True or false:
Waves transfer energy from one place to another and not particles.
K-12 Science, CCSD, 2006
9/17 Wave Properties Notes
IQ: Which wave has a larger amplitude? How can you tell?
K-12 Science, CCSD, 2006
Wave Properties• Amplitude- The distance from the rest position to the
top of a crest, or from the rest position to the bottom of a trough.
• Wavelength- The length of one whole crest and one whole trough=
1 full wave
K-12 Science, CCSD, 2006
• Frequency- The number of full waves passing through a point in one second. SI Unit is hertz. Ex. 10 waves per second = 10 hertz
• What is the frequency if 100 waves pass through a point in 20s?
K-12 Science, CCSD, 2006
Period: The amount of time it takes one wave to pass through a point. Inversely related to f.
T=1/f Unit sec.
Draw into your notes!!
K-12 Science, CCSD, 2006
• Speed- The distance travelled by a wave in a given amount of time, depends ONLY upon the medium. Ex. 100 meters in one second = 100 m/s. Speed= dist./time
• What is the speed of a wave that travels 50 m in 5 secs?
K-12 Science, CCSD, 2006
Wave Speed• The Wave Speedpeed
ttravels– ie: distance a crest or
compression goes in a certain amount of time
• Depends on the medium the wave’s traveling through– Due to density variations– > dense = faster sound
slower light– < dense = faster light
slower sound
Calculating wave speed:
Wave speed (v)Wavelength (Λ)
Frequency (f)
v = Λ X fUnit = meters/sec
(m/s)
Wave speed
(v)
Wavelength(Λ)
Frequency
( f )
K-12 Science, CCSD, 2006
Frequency
Large wavelength = low frequency
Medium wavelength = medium frequency
Small wavelength = high frequency
K-12 Science, CCSD, 2006
Frequency
• Don’t confuse the frequency with the speed of a wave.
• Here’s an analogy:
K-12 Science, CCSD, 2006
FrequencyIf you were looking down on a freeway . . .
And all of the vehicles were going exactly 60 miles per hour (the same speed). . .
K-12 Science, CCSD, 2006
Frequency Small cars going 60 miles per hour
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Frequency Bigger cars going 60 miles per hour
K-12 Science, CCSD, 2006
Frequency Really big vehicles going 60 miles per hour
K-12 Science, CCSD, 2006
Frequency Speed = 60 miles per hour
Small cars = high frequency (6)
Bus = low frequency (1)
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Frequency Light speed = 186,000 miles per second
Blue light waves = higher frequency
Red light waves = lower frequency
K-12 Science, CCSD, 2006
OQ: True or false?
A wave with less frequency can be travelling faster than a wave with higher frequency.
K-12 Science, CCSD, 2006
9/16 p.24 Bill Nye Waves
IQ: Which of the following is the best representation of what probably happens to a sound wave travelling through the same medium over time if no more energy is added?
K-12 Science, CCSD, 2006
OQ: What is the speed of a wave that travels 50m in 100s?
K-12 Science, CCSD, 2006
9/17 Waves Mini labs
What is the frequency of the following wave if it happened over 2s?
Calculate the speed of the wave using v= 20 m
K-12 Science, CCSD, 2006
OQ: What was the source of energy for the waves you made today? What is the medium?
a. The slinky
b. The table
c. Your hand
d. The air
K-12 Science, CCSD, 2006
OQ: Which of the following could NOT be used as evidence to prove that the medium itself does not move during the transfer of energy through a wave? (more than one answer possible)
A. As a wave travels down a rope, the particles of the rope don’t get transferred down.
B. Longer waves travel farther from their source than shorter waves.
C. A piece of string tied to a slinky would not leave its place if a wave is created in the slinky.
D. The soil does not get carried from 1 place to another during an earthquake.