What Is Linear Motion?

Definition

• Linear motion refers to any motion that moves along a straight line in one direction. The direction can either be in a horizontal, vertical or inclined direction. An object in linear motion will maintain the same velocity and direction as long as no external forces act against it. For example, an object that is thrown straight up in the air exhibits linear motion until the force of gravity brings it back down.

Newton's First Law

• Newton's first law of motion also explains linear motion. Formulated by the influential physicist Sir Isaac Newton, the laws of motion explains the movement of all objects and the forces that act against them. According to The Physics Classroom, Newton's first law explains that "an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force."

Unbalanced Force

• Commonly, there are two forces that will act on an object at any given time. If these forces are of equal magnitude and in opposite directions, the object feels a balanced force. An object in linear motion will continue moving if feeling a balanced force. Unbalanced force occurs if the object is acted upon by a force that does not have an equal force present in the opposite direction. The object will accelerate or decelerate, depending on the force, and can even change directions.

Inertia

• An object in linear motion will often resist any changes to its original state of motion. This resistance to external forces is referred to as inertia. An external force acts as a means to being an object in linear motion to rest. The object's mass is a measure of the inertia it has. If the object has more mass, then it also has a greater tendency to resist changes in motion brought on by forces.