Explanation:
Newton’s First Law of Motion, also known as the Law of Inertia, states:
“An object at rest stays at rest, and an object in motion continues in motion with the same speed and in the same direction unless acted upon by a net external force.”
This principle was first clearly formulated by Sir Isaac Newton in the 17th century and is foundational to classical mechanics.
What It Means:
- Objects Resist Change:
- If something is not moving, it will not start moving unless something pushes or pulls it.
- If something is already moving, it will keep moving in a straight line at the same speed unless something causes it to speed up, slow down, or change direction.
- Inertia:
- The tendency of an object to resist changes to its motion is called inertia.
- The greater an object’s mass, the more inertia it has—meaning it’s harder to start or stop its motion.
- Net External Force:
- A net force is the overall force acting on an object after all the individual forces are combined.
- “External” means it comes from outside the object—like friction, gravity, or someone pushing it.
Everyday Examples:
- A book on a table doesn’t move by itself—because no net external force is acting on it.
- A soccer ball continues to roll until friction from the ground and air resistance slow it down.
- In space (where there’s little friction), a spacecraft can move at constant speed without using engines because there’s no significant external force acting on it.
Why It Matters:
This law helps us understand that motion doesn’t need a continuous force to be sustained—it only needs a force to change. This was a major shift from earlier beliefs (like those of Aristotle), who thought that an object would naturally come to rest without a force.