K-1: The Senses
Our Sense of Hearing
What causes sound? How do our ears detect sound? How do our brains recognize sound?
- All of the senses are connected to the brain.
- Our senses let us know what is going on inside and outside our bodies.
- The sense of hearing allows us to detect sounds.
- Sound is produced by vibration.
- Objects vibrate when they move back and forth in a regular fashion.
- Information about sound is collected by sensory receptors in the ears and transmitted to the brain.
Sound is produced when an object vibrates in air (or another medium, such as water) and produces alternating bands of high and low pressure, known as sound waves (or compression waves). Sound waves possess very low levels of energy, but our ears and brain are able to detect the frequency and loudness of many sounds, and to locate sound sources.
The human ear is designed to collect sound waves and detect minute changes in air pressure outside the body. The outer ear consists of the ear flap and a short passageway, known as the auditory canal. The eardrum, or tympanic membrane, is located at the inner end of the auditory canal. It bulges inward or outward in response to pressure changes caused by sound waves. The three tiny, interconnected bones of the middle ear (malleus, incus, stapes) amplify this movement.
Another membrane separates the middle ear from the inner ear, a complicated labyrinth of interconnected fluid-filled chambers and canals called the vestibular system. The upper group of canals is critical to our sense of balance. The lower canal, known as the cochlea, is coiled like a snail shell and filled with fluid. It converts pressure waves into impulses that are sent along sensory neurons to the auditory centers in the brain. A special part of the cerebrum receives and interprets information about sound.
Humans and many other species have specialized organs to produce sounds, such as those in speech or songs, which are important for communication. Most mammals, reptiles and amphibians have a larynx, or voice box, in their necks. The larynx contains the vocal cords, which produce sound as air is expelled from the lungs. The tongue, lips and mouth also have important roles in configuring the sounds produced.
Procedure: Part 1
Discretely start the online metronome. The volume should be just loud enough for students to hear the ticking sound.
Instruct students to sit quietly in a circle around you and tell them to listen carefully for sounds. After a minute or so, have students share their observations. Ask, What sounds did you hear? Did you notice any sound that you don’t normally hear? What do you think is causing the sound? After discussion, reveal the source of the sound and turn it off. Explain that students will be investigating their sense of hearing.
Ask, How are sounds created? Allow students to share ideas. Hold up a large rubber band and stretch it between your hands. Select a student to come up and pluck the rubber band. Have students listen carefully, and ask if they can hear a sound. It may be slight, but they should be able to hear the rubber band. Ask, What did you observe when the rubber band made the sound? (It moved back and forth.) Tell students this rapid back-and-forth motion is called vibration. Ask if they can think of any other place where they have seen vibration. Discuss their ideas.
Hold up the tuning fork. Ask if anyone knows what the object is and/or what it does. Direct students to be very quiet and listen. Make the tuning fork vibrate by holding the handle lightly and striking one of the tines or prongs on the sole of your shoe, or (softly) on a harder-edged surface. Be careful not to strike too hard, as the tuning fork could break.
Ask, What did you hear? Was the sound loud or soft? Strike the tuning fork again and move around the room so that all the students have a chance to hear the sound and observe the tuning fork up close.
Ask, Can you see the tuning fork vibrating? [It is usually not possible to observe the vibration.] Next, ask students to observe what happens when you strike the tuning fork and then dangle the ping pong ball next to it. Ask, What happened? (The ping pong ball will bounce back and forth when it touches the side of the vibrating tuning fork.)
For another demonstration, use an aluminum pie pan half-filled with water. As students look on, strike the tuning fork and immediately place the tip into the water. Ask, What is happening? Students will observe that the water “jumps” when it is contacted by the vibrating tuning fork.
Tell students that they can experience sound caused by vibration in their own bodies. Instruct them to hum softly while placing two fingers on the front of their throats. Ask, Are you making sound? What is moving? Explain that when they hum, talk or sing, or make any sound, air moves inside their throats and across the vocal cords, causing them to move back and forth. Make sure students understand that all sound is caused by vibration.
Tell students that a vibrating object pushes the material (air, water, etc.) that surrounds it. If an object vibrates in air, for example, the air is pushed outward in waves, like the movement they observed with the ping pong ball, or water in the pan. Have students draw and label the tuning fork and ball using wiggly lines to indicate vibration.
- Photo © Diana Dimitrova. Licensed for use.
- Tharp, B., Vu, M., Mock, D., Burnett, C., and Moreno, N. (2015). K-1: The Senses Teacher’s Guide. Baylor College of Medicine, Houston. All rights reserved. ISBN: 978-1-888997-87-3
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Funded by the following grant(s)
National Institutes of Health: Blueprint for Neuroscience Education, National Institute on Drug Abuse and Science Education Partnership Award program, Office of the Director, Division of Program Coordination, Planning and Strategic Initiatives, Office of Research Infrastructure Programs.
The Learning Brain: Interactive Inquiry for Teachers and Students
Grant Number: RD25DA033006