The next time a car, plane, or train passes by, pay attention to the way that the sound changes as it approaches and as it is heading away. You should find that once it passes you, its sound is much different. Why?
To find out, you will need:
- your ears
- a plane, train or automobile passing near you
- a sink or bathtub with enough water to cover the bottom
Why does the sound change? The plane, car, or train is not changing its sound. The difference is that it is now moving away from you instead of towards you. To understand what is happening, put enough water into a sink or bathtub to cover the bottom. Tap your finger into the water and notice the ripples that spread out from it. Basically, the same thing happens when something makes a sound. The sound waves spread in all directions, just as the ripples in the water do. Now, stick your finger into the water and then move it slowly across the surface. Look closely at the ripples. Are they the same in all directions? No. The ripples in front of your finger are closer together, and the ones behind it are farther apart. Again, this is much like the sound waves coming from a moving object. The sound waves in front of a fast moving object are closer together. The closer together the sound waves are, the higher the pitch of the sound. When the plane passes, the sound waves behind it are farther apart and the pitch of the sound is lower. This change in pitch from a moving object is called the Doppler Effect.
If you don't have a place nearby where you can listen to planes, cars, or trains, then ask any child to imitate the sound of an airplane flying overhead. Listen to the sound and you will hear them lower the pitch to simulate the plane going over.
Have a wonder-filled week.
