Consider the impact of non-inertial reference frames on motion (qualitatively in an inertial reference frame, any object subject to zero net force will travel in a straight line at a constant speed. in non-inertial reference frames, an object may appear to travel on a curved path or change speed even though it is subject to zero net force. the following thought experiment will illustrate this. consider a perfectly flat, horizontal turntable (a flat disk rotating about an axis through its center). the turntable is rotating with constant angular velocity o. you are standing next to the turntable on the ground (in an inertial reference frame). you shove a frictionless puck across the turntable straight towards its center. the puck is subject to zero net force in the horizontal direction and travels in a straight line across the turntable as you observe it now, describe the puck's path as observed by someone who is sitting at rest on the turntable. (that observer is rotating along with a fixed point on the turntable which will make the puck appear to deviate from a straight line.)