The supporting phenomena for Principle 7, also known as Newton's first law of motion or the law of inertia, include:
Inertia of an object: An object's tendency to resist changes in its motion. If an object is at rest, it will remain at rest unless acted upon by an unbalanced force. Similarly, if an object is moving at a constant speed in a straight line, it will continue to do so unless acted upon by an unbalanced force.
Conservation of momentum: If the net external force acting on a system is zero, the total momentum of the system remains constant. This implies that objects in motion will continue moving at a constant velocity in the absence of external forces.
Smooth and frictionless surfaces: When an object is placed on a smooth and frictionless surface, it can continue to move at a constant speed and in a straight line due to the absence of external forces such as friction or resistance.
Space travel: In outer space, where there is no significant gravitational or atmospheric resistance, objects can continue moving at a constant speed and in a straight line once set in motion, due to the absence of significant external forces.
Free-falling objects: In the absence of air resistance, objects falling freely near the surface of the Earth experience negligible external forces. As a result, they continue to accelerate downward at a constant rate (due to gravity) without any change in their direction until they encounter other forces like air resistance or contact with the ground.
These phenomena provide evidence and support for the principle that an object will remain at rest or move at a constant speed and in a straight line unless acted upon by unbalanced forces.