Christmas card sales have dropped steadily in recent years. But card companies are using technology to try to keep the tradition alive.
Sound and Vibration Instructorâ€™s Guide
Sound is a form of energy produced by vibrating objects. Without movement there could be no sound. When an object moves or vibrates, the air molecules around the object also vibrate. Vibrating objects (as long as they are not in a vacuum) produce sound. A sound wave contains energy, which in turn means it can make the air around it move. However, if the wave strikes something solid, the wave will bounce backâ€”an echo.
This two-part demonstration uses an aluminum rod and a mixture of cornstarch and waterâ€”oobleckâ€”to show that sound is produced by the vibration of matter.