National Council of Examiners for Engineering and Surveying (NCEES) Fundamentals of Engineering (FE) Other Disciplines Practice Exam

When the sum of the forces acting on a particle is not zero, it indicates that there is a net force acting on the particle. According to Newton's second law of motion, this net force will cause the particle to accelerate. Specifically, the particle will accelerate in the direction of the resultant force. This is fundamental to understanding how forces interact with mass; a net force implies that the object cannot maintain its current state of motion, which is either rest or uniform motion.

In scenarios where the sum of the forces is zero, the particle would either be at rest (if it was motionless) or moving at a constant speed in a straight line (if it was already in motion). However, when there is an unbalanced force, the particle will experience a change in its velocity, which is defined as acceleration.

The other options present alternative outcomes, such as being at rest or moving at a constant speed, which cannot occur if there is a resultant force present. Uniform circular motion also requires a net centripetal force but does not negate the overall principle that a non-zero net force indicates acceleration in response to that force. Thus, the statement that accurately describes the particle's behavior when the forces are unbalanced is that it will accelerate in the direction