Relationship between string length, tension, and pitch
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!)
Tension, Length, & PitchWhat is the effect of tension and length of a vibrating string on the pitch of a sound?
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
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
Sounds in Vibrating Strings• On your whiteboard, identify the two independent variables.• Now identify the dependent variable.
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?
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.
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?
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
Changing Pitch• What about instruments without strings – like a drum?• What do you think vibrates to make sound on a drum?
Changing Pitch• Compare these two drums…what kind of sound do you think each makes?
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.
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?
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.
Changing Pitch• In our investigation, we “measured” pitch by observing the quality of the sound.• Was this a qualitative or quantitative measurement? • qualitative
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?
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)
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
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
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.