• Do Now: Take a clicker. Observe the demo. You have 3 minutes with your group to draw what you see and LABEL the following terms correctly on your drawing:– crest – Trough – Amplitude – Wavelength

• HW: p. 388 #1-9, 11-13 ….Read & Study the corresponding sections in CH. 25 (7 points – ½ point per problem, and 1 point for a randomly graded one)

• PLEASE check the Lost & Found. Claim what is yours – BE HONEST AND DON’T STEAL. Anything left at the end of the year will be trashed or donated

Label the key terms MORE THAN ONCE:crest, trough, amplitude, wavelength

TROUGH is the lowest point on a wave

Label the key terms MORE THAN ONCE:crest, trough, amplitude, wavelength

CREST is the highest point on a wave

Label the key terms MORE THAN ONCE:crest, trough, amplitude, wavelength

Amplitude is the distance from the midpoint to the crest or the

midpoint to the trough

Label the key terms MORE THAN ONCE:crest, trough, amplitude, wavelength

Wavelength is the distance between 2 IDENTICAL,

CONSECUTIVE PARTS of a wave

Label the key terms MORE THAN ONCE:crest, trough, amplitude, wavelength

• CREST is the highest point on a wave • TROUGH is the lowest point on a wave • Amplitude is the distance from the midpoint to

the crest or the midpoint to the trough • Wavelength is the distance between 2 IDENTICAL,

CONSECUTIVE PARTS of a wave

What is a wave?

• A vibration or disturbance.• A wiggle in space and time• Any other definitions? • SOUND & LIGHT are forms of energy that

travel in waves.• However, they travel in different types of

waves… to be discussed later!

Frequency (ƒ)

• How OFTEN /FREQUENTLY a wave happens• # of wave cycles OR wavelengths in one

second.• Measured in Hertz (Hz).• 1 Hz = 1 wavelength OR wave cycle per second• “When a frequency is too high, it HERTZ your

ears!”– Becca Caplinger

Period (T)

• The TIME PERIOD for ONE wavelength / wave cycle

• A period is the time it takes for 1 complete wave length / wave cycle

• 1 cycle = 1 complete trip– 1 trip back & forth, crest to crest – Around and back to the same point (1 wavelength) – 1 wave = 1 cycle

• Measured in seconds

They are INVERSES of each other!!!

• Clapping demo

period = 1 frequency

frequency = 1period

See board for formula in symbols!

Analogy

• One class PERIOD at RHS is 90 minutes. – (time it takes for 1 class = 90 minutes…that’s the

PERIOD)• You have 1 class per 90 minutes, which is how

FREQUENTLY you have classes

T = 90 minutes f = 1 class 90 minutes

• They are inverses!

True or false: When a wave travels in a medium (material) the medium moves

with the wave.

1. 2. 3. 4.

0% 0%0%0%

1. True2. False3. Not enough info4. Not quite sure

DO THE WAVE demo

• Write down your observations…. • It’s not the medium that moves with the

wave… it is the ENERGY that is transmitted! The energy moves!

But wait – what’s a medium?

• It’s not someone who summons spirits.• It’s synonym for material!• Different types of solids, liquids, and gases are

all examples of mediums.• Changing the TEMPERATURE changes the

medium:– Example: temperature in this room vs temp.

outside: different temps, different mediums (even though they are both air!)

Formula in words:

Wave speed = wavelength x frequency

Formula in symbols: Units: (m/s) = (m) x Hz

25.4 Wave Speed The speed of the wave depends on the

______________________________through which the wave movesIf the MEDIUM doesn’t change, then the WAVESPEED doesn’t change! (KEY POINT)

Medium or material

SEE THE BOARD!

You SEE lightening and THEN hear thunder. What does this tell you about

the speed of sound vs. the speed of light?

1. 2. 3. 4. 5.

0% 0% 0%0%0%

1. Light is faster2. Sound is faster3. They are the same

speed4. Not enough info5. Not quite sure

Does wave speed depend on AMPLITUDE (hint - check the formula)?

1. 2. 3. 4.

0% 0%0%0%

1. Yes 2. No 3. Not enough info4. Not quite sure

Slinky Wave Lab• Safety Rules:• All labs must be completed with the slinky FLAT

on the floor• Damaging, twisting, tangling, or otherwise

rendering the slinky useless will result in one or more of the following:– Write up– Loss of lab privileges– You buying me a new slinky

• Have fun! Stopping with 5-10 minutes left for a clicker exit!

Observe the demo: is this a transverse or longitudinal wave?

1. 2. 3. 4.

0% 0%0%0%

1. Transverse2. Longitudinal 3. Not enough info4. Not quite sure

Observe the demo: is this a transverse or longitudinal wave?

1. 2. 3. 4.

0% 0%0%0%

1. Transverse2. Longitudinal 3. Not enough info4. Not quite sure

These waves travel towards each other…

the result is..?

1. 2. 3. 4.

0% 0%0%0%

1. Constructive interference 2. Destructive interference 3. Not enough info4. Not quite sure

They CONSTRUCT a bigger wave!

These waves travel towards each other…

the result is..?

1. 2. 3. 4.

0% 0%0%0%

1. Constructive interference 2. Destructive interference 3. Not enough info4. Not quite sure

They DESTRUCT The wave!

1 0.5

1.5 2

2.5 3

What do your answers tell you about wavelength and frequency? Are they

directly or inversely proportional?

1. 2. 3. 4.

0% 0%0%0%

1. Directly2. inversely3. Not enough info4. Not quite sure

Inversely!!!

λ f = ν = λ f When the waves were MORE FREQUENT,You observed SHORTER WAVELENGTHS!