What property causes objects at rest to remain at rest until acted upon by an outside force?

The property that causes objects at rest to remain at rest until acted upon by an outside force is known as inertia. Inertia is a fundamental concept in physics, specifically described by Newton's first law of motion, which states that an object will remain at rest or in uniform motion in a straight line unless acted upon by a net external force. This means that an object has a tendency to resist changes in its state of motion, whether that means staying still or moving steadily.

In the context of the other options, momentum refers to the quantity of motion an object has, which depends on both its mass and velocity. While it is related to movement, it does not directly explain why an object at rest remains stationary. Friction is a force that opposes motion between surfaces and does not dictate the inherent property of an object's resistance to change in motion. Acceleration is the rate of change of velocity and describes an object's change in motion but does not pertain directly to the state of an object remaining at rest. Thus, inertia is the most accurate term to define the reason objects at rest stay at rest until a force acts on them.