Sense of Hearing

Objective:

The objective of this lab is to learn about your sense of hearing

Background on

Sound is a vibration that typically propagates (spreads out from the original source) as an audible (something that makes a noise) wave of pressure, through something made up of a gas, liquid or solid.

Think of sound as being different sized waves that move through an area. Slow moving, gently bobbing waves have a low tone to them like the deep voice of a grandpa. Fast moving, quick up and down waves have a high tone to them like the screeching of children playing. Sounds waves are made up of high and low pressure, the frequency (how quickly the waves are moving) is determined by measuring the distance between two peaks. The higher the frequency the high pitched the sound, the lower the frequency the lower pitched the sound.

The outside of our ears act like funnels that help isolate and concentrate those sounds into our ear canal. Sound enters the ear and hits the ear drum (tympanic membrane). Think about when you hit a drum, what happens? When you hit a drum it makes noise and vibrates along its top. Our ear drum has sounds come in and hit is just like a mallet hits a normal drum, different sounds produce different vibrations.

Connected to our ear drums are three very tiny but important bones. These bone amplify (increase in strength) the sound waves that have come in an hit the ear drum. The amplification of sound waves by these bones is necessary in order to make certain as much sound hits the cochlea as possible. The bones of the inner ear are the smallest bones in the body and are known as the malleus, incus, and stapes (also known as the hammer, anvil, and stirrup).

After the sound is amplified along the bones of the inner ear it hits the cochlea, which is a spiral-shaped, fluid-filled tube. The cochlea is divided lengthwise by the organ of Corti, which is the main organ the converts the sounds waves into neural impulses. The vibrations cause hair cells inside the organ of Corti to depolarize, depending on which hairs are depolarized helps to create neural impulses that tell our brains what we are hearing.

Materials

• Scissors
• Thin strip of cardstock
• Cellophane
• Cardboard tube
• Cardstock
• Sharp pencil
• Tape
• Rubber band

Method

Prepare Experiment

• Collect all of the materials you will need for the lab and place them neatly in front of you

Run Experiment

1. Draw a circle around the outer diameter of the tube on the cardstock
• Note: you should draw this circle along one of the short edges of the cardstock so you have enough of the paper to use it for the second part of the lab
2. Cut out the circle from the cardstock
3. Use the sharp tip of the pencil to make a small hole in the center of the circle (should be between 2mm and 1 cm)
4. Tape the circle to one end of the tube
5. Using the rubber band, fix the cellophane over the opposite end of the tube, make sure that the cellophane it tight on the end like a drum
6. Fold the cardstock strip so it has a small foot
7. Tape the small foot of the strip to the table with the long end standing up
8. Point the end of the tube with the small hole and paper toward the strip of cardstock, make sure that the hole is lined directly with the paper
9. Gently tap the cellophane end

Analyze Data

When the cellophane is tapped what happens? Does the piece of paper move? What happens if the hole is no longer lined up with the cardstock strip? What happens when the cellophane is loose instead of tight on the end of the tube?

Conclusions

Sound is the movement of waves of different frequencies and magnitudes in the air. A way to visually see the effect of the movement of a soundwave is to create a sound cannon. This simple device when used properly will make a piece of cardstock or paper move when the soundwave hits it.

Make It Your Own

Now try changing the cellophane to another material such as fabric, does it work the same? A fabric such as cotton will absorb much of the sound and the tube will not work as well as with the cellophane. What if instead you change the cardstock circle with the hole in it to another material such as cellophane or fabric?

Extension Activities to do at home

At home see how strong your sound cannon is by pointing at different materials such as plant leaves, books standing on their edge, or an empty plastic cup? What happens when an object is heavier? Can you make a bigger sound cannon using a bucket? How different is it when pointed at a plastic cup or plant leaf?