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Trail Bell Design: Amplitude, Energy and Wavelength

Grade 8 sound wave practice: use a bike-safety club's bell tests to find the amplitude–energy rule, work out wavelengths and pick a bell setting.

Grade 8ScienceInteractive · Printable

Aligned toMS-PS4-1

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What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
10 questions
Classroom-ready

Details

Format: Interactive · Printable
Grade: Grade 8
Subject: Science
Question types: Fill in the blank, Multiple choice, Matching, Circle the answer, Short answer

About this worksheet

What students practice

Students use data to show that a wave's energy grows with the square of its amplitude.
Students use wave speed = frequency × wavelength to find wavelengths of sound waves.
Students use evidence to show that wavelength does not set a sound wave's energy in these tests.

How to use

Use after introducing amplitude, frequency and wavelength. Let students use a calculator, and talk through the rule in Table 1 before they start Part 2.

Curriculum

NGSS standard covered

MS-PS4-1

Use math to describe how a wave's amplitude relates to the energy it carries, and read wavelength and frequency.

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Trail Bell Design: Amplitude, Energy and Wavelength

Use a bike-safety club's sound tests to connect amplitude with energy and frequency with wavelength.

Part 1: The ring test

Read the club's notes and study Table 1. Then answer the questions.

A Bell for the River Trail

1The River Trail through Cedar Falls is shared by bike riders, walkers and people pushing strollers. Walkers often say that riders come up behind them without warning. Many walkers are chatting with friends or listening to music, so a bell that is easy to miss is not much help, but a harsh blast can make people jump into the path of a bike. The bike-safety club at Cedar Falls Middle School decided to design a better trail bell. Eighth graders Ezinne Wexler and Mateo Rourke led the testing, with help from their advisor, Ms. Hollis Nakagawa.

2A bell makes sound when its metal dome vibrates. The dome pushes and pulls on the air next to it, and the air passes the vibration along as a sound wave, a mechanical wave that needs matter to travel through. The frequency is the number of vibrations each second, measured in hertz (Hz). The wavelength is the distance from one squeeze of air to the next, in meters. In air on the test day, sound from every bell traveled at about 340 m/s, and wave speed = frequency × wavelength. The amplitude is how strongly the air is squeezed and stretched as the wave passes.

3The club clamped each bell to a bike in the school parking lot and placed a sound sensor on a stand 5 m away. The sensor showed the amplitude of the sound wave and the energy reaching it, both in the sensor's own units. In the ring test, Mateo rang Bell B four times, pulling the spring-loaded striker back farther each time. Each setting was repeated three times, and Table 1 shows the averages. Bell B's frequency stayed at 1,700 Hz in every ring.

4Next, Ezinne tested four designs: two steel domes of different sizes, a large brass dome and a rubber-bulb horn. She adjusted each striker or squeeze until the sensor showed the same amplitude, 4 units, for every design. Table 2 shows the results.

5The trail managers gave the club a rule for the final design. At 5 m, a bell must deliver at least 25 energy units so that walkers notice it, but no more than 50 units so that it does not startle them.