Module 8 Lesson 6

Module 8—Mechanical Waves

Reflect and Connect

If an airplane is travelling faster than the speed of sound and it passes overhead, you will hear a sonic boom. Will the plane have passed by before you hear the boom?

When a sound source, such as an airplane, travels at the speed of sound, the emitted sound waves travel at the same speed as the object producing them. This causes the waves to pile up and store energy in the form of a shock wave.

Because all the sound waves travel at the same speed in the air (based on constant temperature and pressure), it is easy to predict where the plane will be when the shock wave reaches the observer. Use the simulation titled The location of supersonic airplane to explore this concept. Scroll the browser window to the bottom to see the directions on how to use the simulation. Be sure to click the “Reset” button after you have changed the speed to sound ratio.

Module 8: Lesson 6 Assignment

Remember to submit the answers to D 1, D 2, D 3, and D 4 to your teacher as part of your Module 8: Lesson 6 Assignment.

Discuss

The inside of a police cruiser is shown in this photograph. A radar gun is aimed at a motorist on a highway.

Police use radar (radio detection and ranging) to determine the speed of vehicles on the roadways. The same type of radar is used to measure puck and ball speeds in sports. Research how this technology is related to the Doppler effect, and post a response to the following questions:

D 1. How does radar work?

D 2. What assumptions are made about radio waves in relation to mechanical waves such as sound?

D 3. How does a radar detector work?

D 4. Would a police radar gun work correctly even when the police car is in motion? Explain.

Reflect on the Big Picture

Each of the Reflect on the Big Picture sections in this module deals with waves and transferring energy. To help reinforce your learning from this lesson, complete at least one of the following reflection activities:

Sound that is above the hearing range is known as ultrasound. Do some quick research to see how the Doppler effect is used in medical ultrasound units.
You’ve looked at many examples of sound waves. Now think about light waves. They also appear to change length if the source is moving toward or away from you. Create a drawing in a science-fiction style that incorporates this wavelength change.

Store your completed reflection in your Physics 20 course folder.

Complete the concept map under the heading “Conceptual Overview” on page 435 of your textbook, and store it in your Physics 20 course folder.

Module 8: Lesson 6 Assignment

Remember to submit the Module 8: Lesson 6 Assignment to your teacher.