What would cause an object to change its state of motion according to the law of inertia?

The law of inertia, formulated by Sir Isaac Newton, states that an object at rest will remain at rest and an object in motion will continue in motion at a constant velocity unless acted upon by a net external force. The fundamental aspect of this law is the necessity of an external force to alter the current state of motion of an object.

When an external force is applied to an object, it can either change its speed, its direction, or both. For example, if you push a stationary object, it will begin to move; if you apply brakes to a moving vehicle, it will slow down and eventually stop. Therefore, external forces are the key agents that drive changes in an object's state of motion.

The other choices do not inherently influence an object's state of motion in the way external forces do. Temperature, gravitational variations, or changes in mass do not directly cause an object to change its motion unless they are involved in producing an external force. For instance, while increasing temperature might affect the properties or behavior of materials, it does not modify motion directly. Similarly, a change in gravitational force alters the environment, but it doesn’t necessarily mean there is a force acting on the object unless it results in a new external force acting upon it. A decrease