Teacher Portal

Forms of Energy – Investigation 2 CAP



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Waves are important in science. Students will think of waves as something splashing in the water. They probably will not notice that when waves splash onto the shore that they do so with a fairly regular frequency – that there is a pattern in the way waves move. They will also not yet appreciate that other waves exist that they do not see, such as sound waves, radio waves, and ultraviolet waves. Another important kind of wave are the light waves in the visible range of the wave spectrum. Students will study one form of wave or another throughout their science education.




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In this CAP we will discuss waves. In particular, we will discuss sound waves and how our vocal cords and ears are able to create and receive sound waves, respectively. We will finish with a comparison of sound waves and waves that form on the surface of water.


This slide will jog students’ memory of the lab for Investigation 1. A tuning fork is a wonderful tool to clearly illustrate the connection between vibration and sound. Vibrations cause sound. When the tuning fork is struck on the rubber stopper energy is transferred to the tuning fork and the tines vibrate. This is an example of kinetic energy as the vibrating tines are in motion. The vibrations are quite regular in pattern (frequency) and specific patterns cause us to hear different notes. In the lab, we saw that the tuning fork vibrated and exerted kinetic energy by touching it to the ping-pong ball, which violently “jumped” away when touched.

The kinetic energy pattern of vibrations disturbs the air molecules touching the tuning fork around it. Some kinetic energy is transferred from the tuning fork to the air molecules and they go into motion. These vibrating air molecules strike against other air molecules touching them so that they begin to vibrate as well. The vibrations go from air molecule to air molecule until it reaches our ears – when it does, we perceive a sound wave, we hear a sound!


Let’s start with the generation of a sound wave. Our vocal cords are flaps of tissue stretched across our throats. As we exhale air, it is forced through the vocal cords. By controlling the passage of air through the vocal cord, different vibrations can be achieved. Faster vibrations result in higher-pitched sounds. Slower vibrations result in lower-pitched sounds. By holding one’s hand to one’s throat and making high- and low-pitched sounds, we can easily feel the vibrations of our vocal cords.

Just as in the case with the vibrating tuning fork, the vibrating vocal cords transfer kinetic energy to the air molecules around them. And also, like with the vibrating tines, molecule-to-molecule collisions occur and sound waves leave our mouths and spread across the room.


This slide shows how the ear works. Many of the parts of the ear are labeled in this diagram. The important parts for us are the eardrum (the tympanic membrane) and the stereocilia in the inner ear. Sound waves caused by kinetic vibrations are collected by the conical shape of the outer ear and funneled to the eardrum. The sound waves cause the eardrum to vibrate at the same frequency as the sound wave. Through a complex of three small bones, the vibrations of the eardrum are then transferred to stiff little rod cells called stereocilia. The stereocilia are of different lengths and each vibrates at a different frequency. Nerves connect the stereocilia cells to the brain. Based on which stereocilia vibrate and how hard they vibrate, the brain interprets the nerve impulses as sounds of specific frequencies (pitch) and amplitude (loudness).

Stereocilia a rigid structures but they are also delicate. Exposure to too loud of sounds for extended periods of time can damage them. They lose their rigidity and become flaccid and limp like cooked spaghetti. This prevents them from vibrating correctly until they recover and regain their rigidity. The temporary deafness experienced after walking out of a very loud concert into a quiet night is caused by this type of stereocilia damage. Musicians often protect themselves against permanent hearing loss from prolonged exposure to loud sound by wearing earplugs.


This slide shows an overview of the whole process of initiating and perceiving sound waves. The important concept of this slide is that the disturbance of air molecules by vocal cord vibrations passes through the air as waves of vibrating air molecules. The entire process involves kinetic energy because all of the steps involve the movement of matter (vocal cords, air molecules, eardrum, and stereocilia).


This slide is the same as the last except a wave is drawn in blue to show how a sound wave is represented in science. The peaks of the wave indicate the position of the sound wave and the troughs represent the distance between them. High-frequency vibrations cause sound waves that are closer together while low-frequency vibrations cause sound waves that are further apart. The height of a sound wave (the distance from the bottom of a trough to the top of the next peak indicates its amplitude and is directly related to the energy or loudness of the sound that produces the wave.


This slide shows the type of wave that forms when a drop of water strikes the surface of still water. This type of wave is sometimes easier to understand because it can actually be seen. The waves move in symmetric circles from the source of the kinetic energy of the water droplet. Sound waves also travel away from their source in concentric waves. To help concentrate the sound waves produced by the vocal cords in a specific direction, the speaker might cup their hands around their mouths. Conversely, the listener might cup their hand to their ear to collect more sound wave energy to direct at their eardrum. Both of these behaviors were shown by the two women in the last slide.


This slide shows that the energy of a wave of liquid can cause other materials to move. In the video of this slide, the small light blue ball is seen to move both up and down with the wave, but also it is displaced and moves from left to right as a result of the wave action. 


This summary slide compares the two types of waves discussed in this CAP. Students may observe that both types of waves have peaks and troughs, they both have regular patterns, they both consist of kinetic energy, and so on.