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# Relationship between string length, tension, and pitch

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

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

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### Transcript

• 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, & PitchWhat is the effect of tension and length of a vibrating string on the pitch of a sound?
• 4. 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
• 5. Sounds in Vibrating Strings• On your whiteboard, identify the two independent variables.• Now identify the dependent variable.
• 6. 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?
• 7. Questions You Will Answer1. 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.
• 8. 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?
• 9. 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
• 10. Changing Pitch• What about instruments without strings – like a drum?• What do you think vibrates to make sound on a drum?
• 11. Changing Pitch• Compare these two drums…what kind of sound do you think each makes?
• 12. 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.
• 13. 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?
• 14. 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.
• 15. Changing Pitch• In our investigation, we “measured” pitch by observing the quality of the sound.• Was this a qualitative or quantitative measurement? • qualitative
• 16. 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?
• 17. 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)
• 18. 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
• 19. 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
• 20. Checking Up1. 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.