Table of Contents
What Does Constant Velocity Mean in an Inertial Frame of Reference?
Understand why an object moving at constant velocity in an inertial frame must have zero net force. Learn about Newton’s First Law and force equilibrium.
Question
An object moving at constant velocity in an inertial frame must __________.
A. Eventually stop due to gravity
B. Not have any force of gravity on it
C. Have a net force on it
D. Have zero net force on it
Answer
D. Have zero net force on it
Explanation
According to Newton’s First Law of Motion, an object moving at a constant velocity (which means both constant speed and a constant direction in a straight line) will continue to do so as long as the net external force acting on it is zero. An inertial frame of reference is defined as one in which this law holds true. If there were a net force acting on the object, it would accelerate, changing either its speed or its direction of motion. Gravity might be acting on the object, but if the velocity is constant, there must be an equal and opposite force (like a normal force or air resistance) counteracting it, resulting in a net force of zero.