WAVES
Chapter 25
May 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 =
1
period
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
• They are inverses!
f = 1 class
90 minutes
True or false: When a wave travels in
a medium (material) the medium
moves with the wave.
1.
2.
3.
4.
True
False
Not enough info
Not quite sure
81%
12%
8%
0%
1
2
3
4
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!)
25.4 Wave Speed
The speed of the wave depends on the
______________________________
through which the wave moves
If the MEDIUM doesn’t change, then the WAVESPEED
doesn’t change! (KEY POINT)
Formula in
words:
Formula in
symbols:
Units:
Wave speed = wavelength x frequency
(m/s)
=
(m)
x
Hz
You SEE lightening and THEN hear
thunder. What does this tell you about
the speed of sound vs. the speed of
light?
1. Light is faster
2. Sound is faster
3. They are the same
speed
4. Not enough info
5. Not quite sure
100%
1
0%
0%
2
3
0%
0%
4
5
Does wave speed depend on
AMPLITUDE (hint - check the formula)?
1.
2.
3.
4.
Yes
No
Not enough info
Not quite sure
73%
23%
0%
1
2
3
5%
4
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.
Transverse
Longitudinal
Not enough info
Not quite sure
0%
1
0%
2
0%
3
0%
4
Observe the demo: is this a
transverse or longitudinal wave?
1.
2.
3.
4.
Transverse
Longitudinal
Not enough info
Not quite sure
0%
1
0%
2
0%
3
0%
4
These waves
travel towards
each other… the
result is..?
1.
2.
3.
4.
Constructive interference
Destructive interference
Not enough info
Not quite sure
0%
1
0%
2
0%
3
0%
4
These waves travel
towards each other…
the result is..?
1.
2.
3.
4.
Constructive interference
Destructive interference
Not enough info
Not quite sure
0%
1
0%
2
0%
3
0%
4
What do your answers tell you about
wavelength and frequency? Are they
directly or inversely proportional?
1.
2.
3.
4.
Directly
inversely
Not enough info
Not quite sure
0%
1
0%
2
0%
3
0%
4
Inversely!!!
λf =
ν =λ
f
When the waves were MORE FREQUENT,
You observed SHORTER WAVELENGTHS!