Effect of Tension, Length of String on Frequency

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Ms. Parker's notes for chapter 5, section 1

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Effect of Tension, Length of String on Frequency

  1. 1. Good Afternoon!<br />Today we will:<br />conduct an investigation<br />write a conclusion about our investigation<br />take some notes<br />Please do before the tardy bell:<br />get your science notebook<br />get a whiteboard and marker<br />get a textbook<br />get out something to write with (besides my marker!) <br />
  2. 2. Tension, Length, & Pitch<br />What is the effect of tension and length of a vibrating string on the pitch of a sound?<br />
  3. 3.
  4. 4. In Your Lab Notebook<br />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.<br />Turn in your textbook to page 484<br />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.<br />1-2-4<br />
  5. 5. Sounds in Vibrating Strings<br />Read the “Investigate” on pages 484 – 486.<br />When you are finished reading, you should know:<br />the two different independent variables you will be testing<br />the one dependent variable you will be evaluating<br />you have 7 minutes<br />
  6. 6. Sounds in Vibrating Strings<br />On your whiteboard, identify the two independent variables.<br />Now identify the dependent variable.<br />
  7. 7. Sounds in Vibrating Strings<br />In your lab book, write two hypothesis statements: one of each independent variable.<br />What safety precautions should you take in this lab?<br />
  8. 8. Questions You Will Answer<br />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?<br />When you decrease the length of a string in an instrument, how does the pitch of the sound you hear change?<br />Using the terms tension, length, pitch, and frequency describe how to change the quality of sound.<br />
  9. 9. Changing the Pitch<br />To produce sound (any sound) something must vibrate.<br />Everything that vibrates produces a sound.<br />In the lab, we saw that shortening the string affected the pitch of the sound…<br />what happened to the pitch when the string was shortened?<br />
  10. 10. Changing Pitch<br />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<br />
  11. 11. Changing Pitch<br />What about instruments without strings – like a drum?<br />What do you think vibrates to make sound on a drum?<br />
  12. 12. Changing Pitch<br />Compare these two drums…what kind of sound do you think each makes?<br />
  13. 13. Changing the Pitch<br />With instruments like drums, the “length of the string” is the size of the drumhead.<br />The larger the drumhead, the lower the pitch.<br />
  14. 14. Changing Pitch<br />The other independent variable we tested in the investigation was tension.<br />Tension: how tight a string or wire is stretched.<br />How did we change the tension of the string?<br />What happened to the pitch of the sound when the tension was increased?<br />
  15. 15. Changing Pitch<br />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.<br />
  16. 16. Changing Pitch<br />In our investigation, we “measured” pitch by observing the quality of the sound.<br />Was this a qualitative or quantitative measurement?<br />qualitative<br />
  17. 17. Types of Measurements<br />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<br />What would be necessary to make a quantitative measurement of pitch?<br />
  18. 18. Pitch & Frequency<br />The higher the pitch of a sound, the greater the frequency.<br />frequency:the number of cycles a vibration makes in a given time period (almost always a second)<br />
  19. 19. Independent & Dependent Variables<br />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?<br />length of string<br />
  20. 20. Graphing<br />On your whiteboard, create a graph for length of string versus frequency of sound.<br />Sketch what you believe the shape of the line should be.<br />frequency<br />length of string<br />
  21. 21. Checking Up<br />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?<br />When you decrease the length of a string in an instrument, how does the pitch of the sound you hear change?<br />Using the terms tension, length, pitch, and frequency describe how to change the quality of sound.<br />

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