Notes from Ms. Parker's 9th grade Physics class week of Jan 17 - 20, 2012

1. Good Afternoon!
• Today we will:
• conduct an investigation
• write a conclusion about our investigation
• take some notes
• Please do before the tardy bell:
• get your science notebook
• get a whiteboard and marker
• get a textbook
• get out something to write with (besides my marker!)


2. Tension, Length, &
Pitch
What is the effect of tension and length of a vibrating string on
the pitch of a sound?

4. In Your Lab Notebook
• Turn to the first clean page in your lab book and
title it, “Sounds in Vibrating Strings.” Be sure to
make an entry in your Table of Contents as well.
• Turn in your textbook to page 484
• read the “What do You Think” section and write
your answers the two questions in your lab book –
use complete sentences that restate the
question, please.
• 1-2-4

5. Sounds in Vibrating
Strings
• Read the “Investigate” on pages 484 –
486.
• When you are finished reading, you should
know:
• the two different independent variables
you will be testing
• the one dependent variable you will be
evaluating
• you have 7 minutes

6. Sounds in Vibrating
Strings
• On your whiteboard, identify the two
independent variables.
• Now identify the dependent variable.

7. Sounds in Vibrating
Strings
• In your lab book, write two hypothesis
statements: one of each independent
variable.
• What safety precautions should you
take in this lab?

8. Questions You Will Answer
1. What happens to the pitch of the sound produced
by a string when its tension is increased? How
did you increase tension in the investigation?
2. When you decrease the length of a string in an
instrument, how does the pitch of the sound you
hear change?
3. Using the terms tension, length, pitch, and
frequency describe how to change the quality of
sound.

9. Changing the Pitch
• To produce sound (any sound)
something must vibrate.
• Everything that vibrates produces a
sound.
• In the lab, we saw that shortening the
string affected the pitch of the sound…
• what happened to the pitch when the
string was shortened?

10. Changing Pitch
• When you play the guitar, you change the length
of the string by pressing your fingers down on
strings at different places along the neck of the
guitar

11. Changing Pitch
• What about instruments without
strings – like a drum?
• What do you think vibrates to make
sound on a drum?

12. Changing Pitch
• Compare these two drums…what
kind of sound do you think each
makes?

13. Changing the Pitch
• With instruments like drums, the
“length of the string” is the size of the
drumhead.
• The larger the drumhead, the lower
the pitch.

14. Changing Pitch
• The other independent variable we tested in
the investigation was tension.
• Tension: how tight a string or wire is
stretched.
• How did we change the tension of the
string?
• What happened to the pitch of the sound
when the tension was increased?

15. Changing Pitch
• String instruments such as guitars or violins
have pegs attached to the end of a string. A
musician adjusts the string tension by
turning the peg.

16. Changing Pitch
• In our investigation, we “measured”
pitch by observing the quality of the
sound.
• Was this a qualitative or quantitative
measurement?
• qualitative

17. Types of Measurements
• Remember: “qualitative” refers to the
quality of something: the quality of a
taste, feel, smell, sound whereas
“quantitative” refers to a
measurement with a number – a
quantity
• What would be necessary to make a
quantitative measurement of pitch?

18. Pitch & Frequency
• The higher the pitch of a sound,
the greater the frequency.
• frequency: the number of cycles
a vibration makes in a given time
period (almost always a second)

19. Independent & Dependent
Variables
• If you wanted to test the effect of the
length of a string on the frequency of
sound it produces, what would your
independent variable be?
• length of string

20. Graphing
• On your whiteboard, create a graph for
length of string versus frequency of sound.
• Sketch what you believe the shape of the
line should be.
frequency
length of string

21. Checking Up
1. What happens to the pitch of the sound
produced by a string when its tension is
increased? How did you increase tension in
the investigation?
2. When you decrease the length of a string in an
instrument, how does the pitch of the sound
you hear change?
3. Using the terms tension, length, pitch, and
frequency describe how to change the quality
of sound.