[narrator with harp, narrator speaking:] This harp produces sounds with many different frequencies, ranging as high as 3,000 hertz, to as low as 30 hertz. An example such as this harp show, one reason sounds are not all alike is that they have different frequencies, and the frequency of the sound determines wether it’s high or low or in between. The highness or the lowness of sounds is called, pitch. [video of card placed in bicycle spokes, wheel turning ] There is a simple experiment that clearly shows how pitch depends on the frequency of the sound, the number of vibrations per second. You take an ordinary playing card, and attach it to the rear wheel of a bicycle with a close pin. Turn the bicycle upside down and you can do this more easily. One edge of the playing card should just touch the wheels spokes. Now turn the wheel very slowly. Each times a spoke hits the card the card vibrates. Notice how when you turn the wheel slowly the pitch is low, and as you turn it faster and faster the pitch gets higher and higher. The faster something vibrates the greater it’s frequency, and the higher it’s pitch.

It’s important to remember that pitch and volume are not related. Volume referrers to how loud or soft a sound is. Pitch referrers to how high or low a sound is. We can see these distinctions in our own voices. I can change the volume of my voice by talking more softly or more loudly. I can also change the pitch of my voice. I can talk with a high pitch, or with a pitch that is lower. We change the volume and pitch of our voices all the time in the course of a conversation. In fact, our speech would be very flat and unnatural if we didn’t change its volume and pitch.