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

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• 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). . .

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Frequency Small cars going 60 miles per hour

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Frequency Bigger cars going 60 miles per hour

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Frequency Really big vehicles going 60 miles per hour

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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

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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.