How does inertia affect the motion of a puck?
In the absence of friction, the inertia of a puck will keep it moving in a straight line at a constant speed.
The inertia of an object is its tendency to resist changes in velocity. The more inertia an object has (which is measured by the mass of an object), the harder it is (the more force it takes) to change its velocity (which is the object's speed and its direction of motion).
Newton's First Law (also called the Law of Inertia) states that an object at rest will stay at rest unless there is an unbalanced force that acts on it, and an object in motion will continue in motion at a constant velocity (constant speed in a straight line) unless there is an unbalanced force (also called a net force) acting on the object.