Doctors use the stethoscope to amplify the sounds in the body. In this video a simple stethoscope is made using a funnel, tube and a balloon. The balloon is stretched across the wide end of the funnel like a diaphragm. The narrow end of the funnel is inserted into a tubing. When the balloon diaphragm is pressed against the chest it picks up the sound waves emanating from there and vibrates. These vibrations create pressure waves in the air inside the funnel. These are channeled into the tubing where they undergo multiple reflections and reach the ears of the listener with an amplified effect.