Students examine a brief history of the discovery of how sound works and then use tuning forks to experiment with how sound works.
History of sound
Conservation of energy
Students will be able to…
• Relate the frequency of notes that are an octave apart – twice the frequency
• Identify the frequency of tuning fork that can cause another fork to vibrate/resonate
• Identify whether a tuning fork will make a low or high note based on the tine length
• Describe the transfer of energy from a tuning fork to either another turning fork or to water
Materials in Kit
Tuning forks – 1 per group
Materials Not in Kit
Containers for water – 1 per group
Gather materials and set up computer with the PhET simulator “Wave on a String” if you would like to use it.
Introduce the Activity
Students will read the excerpt (see page 4) on the discovery of sound and answer questions 1-5. This will be done at the beginning of class.
The point to emphasize in the reading is that it took a very long time to discover what creates sound, and to emphasize how turning forks helped the process along.
Students will answer prediction questions 6 and 7.
Doing the Activity
Tuning Fork Discovery
NOTE: Question 6 is only appropriate if the set of tuning forks are uniform (as the ones in the kit are). If they are different brands or have tuning knobs on the ends, this question won’t work.
1. Students will walk around to other tables and compare their tuning fork to other groups.
→ They should find at least 5 different comparisons using a chart like the one below.
→ Students should then answer questions 8a and 8b
2. Have the students test other frequencies of tuning forks to see if one fork that is already vibrating can make another fork start vibrating by simply holding them next to each other – do not physically touch them.
WARNING: be sure that the quite fork is completely silenced first. Hold the tines firmly in your hand to silence the fork before beginning the test.
→ Students will answer 8c and 9 based on the information about the frequencies of tuning forks.
3. Have the students place the vibrating turning fork in a cup of water and then answer question 10. The smaller the container used, the bigger the splash will be! Also the lower frequency tuning forks make lager splashes.
A musical note one octave higher than the previous is twice the frequency of the previous. For example, middle C is 261.5 Hz and the next C is an octave higher at 523 Hz, while the next octave up has a C of 1046 Hz.
A vibrating tuning fork can cause another quiet tuning fork to start vibrating simply by being placed near each other. No need to touch them or to have them both touching a table. The energy transfers through the air. The frequencies of the two forks have to be the same for best results. Frequencies that are near, for example 880 Hz and 883 Hz, will not work. However, multiples of frequency can work but are more quite. For example, 440 Hz and 880 Hz.
The tuning forks included in the ASA Activity Kit for Teachers are all manufactured with the same material so a person can look at the tine length and see that lower frequency tuning forks have longer tines while higher frequency forks have shorter tines.
When a vibrating tuning fork is placed in a bowl of water, the energy from the fork is transferred into the water. If the fork just touches the water, a small amount of water from the top gains kinetic energy and flies out of the bowl. If you dip the fork deeply, the vibrations quit. This is because the energy is transferred to a lot of water which is too heavy to move very fast with the small amount of energy that the tuning fork vibrates with.
Key Lesson Terminology
Frequency – wiggles per second (moves back and forth)
Resonance – A natural frequency of vibration determined by the size and shape of an object
Pitch – How low or high a tone sounds to a person
Hertz (Hz) – A measure of frequency. The number of oscillations (back and forth movements) per second.
If necessary, the paragraph on the history of sound could be read aloud and the questions afterward can be done through class discussion.
Art Extension – If you put the tuning fork in a cup of paint (the runnier the paint, the better) it will splash onto a piece of paper