Why Is Inertia Important?

Inertia as a Concept

• Put simply, inertia is the idea that an object will keep moving unless an outside force acts to stop it. This principle states that an object will move at a constant speed and in a constant direction unless something outside of it acts to change it. For example, a ball rolling across the floor will either stop once it hits a wall or change its direction and speed.

Newton's Discovery of Inertia

• Known as Newton's "First Law of Motion," the concept of inertia was clarified in Newton's book "Mathematical Principles of Natural Philosophy," for which he recieved international acclaim. Written in 1687, this text, and its three laws of motion, became a basis for modern physics. However, this was not the initial discovery of inertia; Newton himself credits Galileo on first understanding inertia.

Inertia, Friction and Gravity

• Newton's understanding of inertia also helped him better understand gravity and friction. Because the principle of inertia states that an object will keep moving unless something acts against it, Newton had to explain what might cause an object to slow down or stop moving. Friction is one factor that acts against objects to stop them or slow them down. The pull of gravity also does this by anchoring objects to the earth.

Baseball: Inertia in Action

• The game of baseball provides a perfect example of the concept of inertia. When the pitcher pitches the baseball, the ball will move at a constant speed and constant direction toward the batter. The principle of inertia states that the ball will keep moving toward the batter unless something acts against it. Once the batter hits the ball, the baseball changes direction and speed. Therefore, the batter's bat acts as the external force changing the ball's initial inertia.