# Without friction, what net force is needed to maintain a 1000 kg car in uniform motion for 30 minutes?

None. Applying Newton's First Law of Motion, this object will continue its state of uniform speed in a straight line until a net (unbalanced) force acts upon it.

Newton's first law:

##### An object at rest remains at rest, or if in motion, remains in motion at a constant velocity unless acted on by a net external force.

A force is a push or a pull exerted on one object by another object. The units of force F are called Newtons or simply N.

An external force is a force originating from outside an object rather than a force internal to an object. For instance, the force of gravity that Earth exerts on the moon is an external force on the moon. However, the force of gravity that the inner core of the moon exerts on the outer crust of the moon is an internal force on the moon. Internal forces within an object can't cause a change in that object's overall motion.

The net force, written as ΣF, on an object is the total force on an object. If many forces act on an object, then the net force is the sum of all the forces. But be careful—since force F is a vector, to find the net force ΣF, the forces must be added up like vectors using vector addition.

Newton's first law says that if the net force on an object is zero (ΣF=0), then that object will have zero acceleration. That doesn't necessarily mean the object is at rest, but it means that the velocity is constant. In other words, constant zero velocity—at rest—or constant non-zero velocity—moving with a constant velocity.

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