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**Physics Chapter 5 Section 3**

Sounds in strings revisited

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**HW: p 517 #1-5 Do Now: Agenda 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

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**Investigate 5.3 (Guidelines for 1-7)**

Same set-up as Investigation 1 What kind of wave is the string making? How do you calculate wavelength? Standing Wave - this is similar to the waves made in the spring The wavelength is twice the length of the string

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**Sample Data Table String Length Wavelength**

(2x string length) Pitch (high, low, or medium)

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**Investigation 5.3 (Guidelines for 8-12)**

Complete with your group Remember that speed is distance traveled over a period of time.

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Summary/Exit Ticket How does changing the wavelength effect the velocity? How does changing the frequency effect the velocity?

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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

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**Physics Talk 5.3 What kind of wave does the vibrating string produce?**

How do you calculate the wavelength? A standing wave The wavelenght is twice the length of the string

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**Physics Talk 5.3 How does frequency relate to pitch?**

Equation for wave speed The higher the frequency, the higher the pitch Wave speed = wave frequency x wavelength

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**Physics Talk 5.3 How do we solve for frequency?**

Rearrange the equation to read

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Physics Talk 5.3 What happened when you shortened the length of the string? How is this shown in the equation? The wavelength was shortened Pitch increased Frequency increased 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

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Physics Talk 5.3 What kind of mathematical relationship does this show? What is an inverse relationship? Inverse Relationship A relationship where when one value increases, the other decreases, or as one value decreases, the other increases

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Physics Talk 5.3 How is frequency an example of an inverse relationship? Decreasing the wavelength increases the frequency

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**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)

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**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

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**Physics Talk 5.3 What is a direct relationship?**

Example of direct relationship A relationship where as one value increases, the other value also increases Increasing the wave speed also increases the frequency and pitch

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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

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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

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**Physics Talk 5.3 When do standing waves occur?**

How does string length related to standing waves? When the length of the coiled spring or string has a certain relationship The length much be 1/2, 1, 3/2, 2, etc of the wavelength

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**Physics Talk 5.3 Equation for standing waves**

Standing waves occur when the the following equation is met: L = string length n = a whole number (1, 2, 3, etc) Lambda = wavelength

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**Physics Talk 5.3 How do you calculate the period for a wave?**

How is a period related to the frequency? T is the period The frequency is the reciprocal of the period

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**Sample Problems 1 and 2 p 513 Use GUTS When in doubt, draw it out**

Pictures are very helpful!

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What do you think now? Why does the pitch change when you change the tension in the string? USE PHYSICS!

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