Transcript Physics Chapter 5 Section 3

Physics Chapter 5 Section 3
Sounds in strings revisited
HW: p 517 #1-5
 Learning Objective
 Explain direct and inverse relationships
 Explain how wave speed, wavelength, and
frequency are related
 Create a data table to organize data for
experiments.
 Success Criteria
 Describe what determines wavelength and
sound
 Describe the relationship between tension and
speed of a wave
 Describe the relationship between wavelength
and frequency
 Determine the velocity of a wave using the
equation
 Calculate wavelength of a standing wave
 Describe how the pitch of the sound produced
by a vibrating string depends on the wave
speed, wavelength and frequency of the waves
on the string.
 Do Now:
 Write LO and SC
on new left page
 WDYS/WDYT on
page 508
 Agenda
 Do Now
 Investigation 5.3
 Summary/Exit
Ticket
Investigate 5.3
 Same set-up as
Investigation 1
 What kind of wave is
the string making?
 How do you calculate
wavelength?
(Guidelines for 1-7)
 Standing Wave - this
is similar to the
waves made in the
spring
 The wavelength is
twice the length of
the string
Sample Data Table
String Length
Wavelength
(2x string length)
Pitch (high, low,
or medium)
Investigation 5.3
 Complete with your
group
 Remember that
speed is distance
traveled over a
period of time.
(Guidelines for 8-12)
d
s
t
Summary/Exit Ticket
 How does changing
the wavelength effect
the velocity?
 How does changing
the frequency effect
the velocity?
HW: p 517 #1-5


Learning Objective

 Explain direct and inverse relationships
 Explain how wave speed, wavelength, and frequency
are related
 Create a data table to organize data for experiments.
Success Criteria
 Describe what determines wavelength and sound
 Describe the relationship between tension and speed
of a wave
 Describe the relationship between wavelength and

frequency
 Determine the velocity of a wave using the equation
 Calculate wavelength of a standing wave
 Describe how the pitch of the sound produced by a
vibrating string depends on the wave speed,
wavelength and frequency of the waves on the string.
Do Now:
 If you keep the
wavelength the
same, how can
you change the
velocity of the
wave?
Agenda
 Do Now
 Notes 5.3
 Summary/Exit
Ticket
Physics Talk 5.3
 What kind of wave
does the vibrating
string produce?
 A standing wave
 How do you calculate
the wavelength?
 The wavelenght is
twice the length of
the string
Physics Talk 5.3
 How does frequency
relate to pitch?
 The higher the
frequency, the higher
the pitch
 Equation for wave
speed
 Wave speed =
wave frequency x
wavelength
v  f
Physics Talk 5.3
 How do we solve for
frequency?
 Rearrange the
equation to read
f 

v

Physics Talk 5.3
 What happened
when you shortened
the length of the
string?
 The wavelength was
shortened
 Pitch increased
 Frequency increased
 How is this shown in
the equation?
 Dividing by a smaller
number on the
bottom, gives us a
larger frequency
 If you have to share
something with fewer
people, you get more
Physics Talk 5.3
 What kind of
mathematical
relationship does this
show?
 Inverse Relationship
 What is an inverse
relationship?
 A relationship where
when one value
increases, the other
decreases, or as one
value decreases, the
other increases
Physics Talk 5.3
 How is frequency an
example of an
inverse relationship?
 Decreasing the
wavelength increases
the frequency
Physics Talk 5.3
 How are tension and
pitch related?
 Since the wavelength
did not change, and
the frequency
increased, this means
the wave speed
increased
 An increase in
tension, produces a
larger force, which
leads to a larger
acceleration on the
string (F=ma)
Physics Talk 5.3
 How are tension and
pitch related?
(continued)
 When the force
accelerates the
string, the wave
speed increases and
the string vibrates
faster
 Since the wave is
faster, the frequency
must also be faster,
leading to a higher
pitch
Physics Talk 5.3
 What is a direct
relationship?
 A relationship where
as one value
increases, the other
value also increases
 Example of direct
relationship
 Increasing the wave
speed also increases
the frequency and
pitch
Physics Talk 5.3
 How does increasing
the thickness of the
string lead to a
different pitch?
 When the string is
larger, it has a
greater mass for the
wave to travel
through
 This also means it
takes more force to
stop the string from
vibrating
 The force is the
tension in the string
Physics Talk 5.3
 How does increasing
the thickness of the
string lead to a
different pitch?
 Since the mass is
heavier, the
acceleration will be
less (F=ma)
 This creates a slower
wave speed
 Decreasing wave
speed will decrease
the frequency and
pitch
Physics Talk 5.3
 When do standing
waves occur?
 When the length of
the coiled spring or
string has a certain
relationship
 How does string
length related to
standing waves?
 The length much be
1/2, 1, 3/2, 2, etc of
the wavelength
Physics Talk 5.3
 Equation for standing
waves
 Standing waves occur
when the the following
equation is met:
n
L
2
L = string length
n = a whole number (1, 2, 3,
etc)
Lambda = wavelength

Physics Talk 5.3
 How do you
calculate the
period for a
wave?
 How 
is a
period related
to the
frequency?
time_ for_ x _vibrations
T
x
 T is the period
 The frequency is the
reciprocal of the
period
1
f 
T
Sample Problems 1 and 2
 p 513
 Use GUTS
 When in doubt, draw it out
 Pictures are very helpful!
What do you think now?
 Why does the pitch change when you
change the tension in the string?
USE PHYSICS!