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Whelmer #67: Bells in Your Ears
 Description:
The transmission of sound waves through solid objects is demonstrated.
Science process skills:
- observation
Complex reasoning strategies:
- induction
Standards:
K-4:
- Employ simple equipment and tools to gather data and extend the senses
(Standard A.1.3).
- Sound is produced by vibrating objects (Standard B.2.4).
5-8:
- Energy is a property of many substances and is associated with sound.
Energy is transferred in many ways (Standard B.3.1).
9-12:
- Waves, including sound, have energy and can transfer energy when they
interact with matter (Standard B.6.1).
Above Standards from the National
Science Education Standards.
Content topics:
- sound waves
You will need:
- pencils with erasers
- string
- metal forks and spoons
- scissors
Instructions:
When the reference is made in this activity to "stick it in your ear;"
caution students that it is dangerous to insert foreign objects deep into
the auditory canal. For the purpose of this activity, the eraser end of
a pencil needs only to be touched gently against one of the ridges of the
outer ear. With younger children, a finger can be substituted for the pencil
in this activity.
Cut a 12 inch (30 cm) piece of string. Tie a metal fork to one end of the
string. Tie the other end to a new pencil (with eraser).
Use one hand to hold the eraser end of the pencil gently against a ridge
in the outer ear. Hold a spoon in the other hand. Allow the fork to hang
freely. Strike the fork with the spoon. Sound waves from the vibrating fork
will travel through the string and pencil to the ear. The sound resembles
that of a church bell.
Presentation:
Caution students about the hazards of placing foreign objects in their ears!
Before touching your ears with the pencil, strike the fork and allow it
to vibrate. Direct students to make observations concerning the sound they
hear. (pitch, loudness, duration, etc.) Ask them to describe the path sound
waves are taking to their ear.
Ask students to predict what they will hear, if anything, when the end of
the pencil is placed in their ear. Will the sound waves travel through the
string as well as through the air? What differences will traveling through
a solid object make on sound waves? Ask them to consider whether sound waves
would travel faster through a solid object or through air? (Would it be
easier to run on pillows, or a hard pavement?)
Content:
Under standard conditions, sound travels through air at 340 meters per second,
or ~750 miles per hour. Sound travels more than seven times as fast through
the string and the pencil.
The more rigid a substance is, the faster sound travels through it.
Sound waves are a series of compressions and rebounds of the medium through
which it is traveling. The molecules of solid objects are more tightly packed
together than liquids or gases. Molecules of solids do not need to travel
as far to "pass the compression wave" on to the next molecule.
The sound traveling through the string is much louder because most of the
wave energy is directed through the string only, and not dissipated in surrounding
air.
Assessment:
Type: small group.
Content/Process: sound waves.
Age/Level: all.
Give groups of 3-4 students a slinky (either metal or plastic). Use the
slinky to illustrate a compression wave. Students will want to move the
stretched slinky up and down. Compression waves are formed by pushing a
stretched slinky toward the other end. Students should use the slinky to
explain how sound travels through the string to the ear. Students can also
illustrate what occurs when two waves begin at opposite ends of the slinky
and collide (interference).
Notes:
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