Welcome to Newton's First Law of Motion. This fundamental principle states that an object at rest will stay at rest, and an object in motion will continue moving at constant velocity in a straight line, unless acted upon by a net external force. This law is also known as the Law of Inertia, describing an object's natural tendency to resist changes in its state of motion.
Let's examine the first part of Newton's First Law: objects at rest. When an object is at rest, it will remain at rest unless acted upon by a net external force. Consider a book sitting on a table. The book experiences two forces: its weight pulling downward, and the normal force from the table pushing upward. Since these forces are equal and opposite, the net force is zero, and the book remains at rest.
Now let's examine objects in motion. According to Newton's First Law, an object in motion will continue moving at constant velocity in a straight line unless acted upon by a net external force. This is best demonstrated in space, where there is no friction or air resistance. A spacecraft will continue moving at constant velocity indefinitely, requiring no additional force to maintain its motion.
What happens when forces do act on an object? When a net external force acts on an object, its state of motion changes, and the object will accelerate. Consider pushing a box on the ground. The applied force pushes the box forward, while friction opposes the motion. If the applied force is greater than friction, there is a net force, and the box will accelerate in the direction of the net force.
To summarize Newton's First Law: objects at rest will stay at rest, and objects in motion will continue moving at constant velocity, unless acted upon by a net external force. This fundamental principle, also known as the Law of Inertia, helps us understand how forces affect motion in our everyday world.