…doctors need stethoscopes. 

Doctors need stethoscopes to listen to their patients’ lungs, heart and other organs. A stethoscope is made of three parts—a chest piece, tubing and a headset. The chest piece has a diaphragm (that acts like our eardrum) and a hollow, bell-shaped metal with a hole on top. As the heart beats, it gives out vibrations. These vibrations are picked up by the diaphragm in the chest piece and transported to the headset via the tubing. The small bell-shaped metal in the chest piece helps doctors listen to heart murmurs or soft whooshing sounds in our hearts

…erasers help erase pencil marks. 

When we write something on a paper with a pencil, the graphite particles from the pencil stick to the paper’s surface. Erasers work because most of them are made from petroleum-based rubber. This makes the eraser stickier than the paper. When we use the eraser on the paper, the graphite particles transfer to the eraser, leaving behind a neat and clean paper!  Until the 1770s, people used moist balls of bread as erasers! 

…birds decide to migrate. 

Scientists believe that birds migrate when they sense lower temperatures and changes in the day’s length and food supply. While we don’t fully understand how birds navigate when they’re migrating, experts have some theories. They believe that birds keep track of their direction through the positions of the Sun and stars, and through the Earth’s magnetic field. Some birds even remember landmarks they see during the day. Scientists have found evidence that smell plays a big role in helping homing pigeons navigate.