WAVES

Chapter 25May 2 & 3

• Do Now: Turn in HW. Take a clicker. Observe the demo. Teacher will assign groups – you have 3 minutes with your group to draw what you see and LABEL the following terms correctly:– crest – Trough – Amplitude – Node

• HW: p. 388 #1-9, 11-13 in the POST section of your packet. *Will not be collected, but expect an open notes quiz to see if you completed the assignment * (This will be the case from now until the end of the year…you will have a few projects, several quizzes/labs, 1 test, and 1 Quest, and a Final exam.)

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!

On your paper, try to label the key terms MORE THAN ONCE:

crest, trough, amplitude, wavelength

Using your vocab HW…

• Fill out the ‘frequency’ and ‘period’ boxes.• We will review in a few moments.

Frequency (ƒ)

• How OFTEN a wave happens• How FREQUENTLY a wave happens• # of cycles in one second.• # of waves in one second.• Measured in Hertz (Hz).• 1 Hz = 1 cycle per second• “When a frequency is too high, it HERTZ your

ears!”– Becca Caplinger

Period (T)

• The TIME PERIOD for one wave• A period is the time it takes for one cycle.• 1 cycle = 1 complete trip– 1 trip back & forth– Around and back to the same point– 1 wave = 1 cycle

• Measured in seconds

period = 1 frequency

frequency = 1period

See board for formula in symbols!

Analogy• One class PERIOD at Rville is 90 minutes.

(time it takes for 1 class)• 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

81%

8%0%

12%

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

Jump rope 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

100%

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

23%

5%0%

73%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!