If the sum of the forces on a particle is not equal to zero, the particle is?

The situation where the sum of the forces acting on a particle is not equal to zero indicates that there is a net force acting on the particle. According to Newton’s second law of motion, this net force causes the particle to accelerate. The key point is that acceleration occurs in the direction of the net (resultant) force acting on the particle.

When a resultant force is present, it indicates that there is an imbalance in the forces acting on the particle, which causes a change in the particle's state of motion. The particle does not simply maintain its motion; instead, it responds to the net force, leading to an acceleration.

Therefore, if the net force is directing a specific way, the particle will accelerate in that same direction, aligning with the correct answer. This principle is fundamental in classical mechanics and is essential for understanding dynamics and the behavior of moving objects under the influence of forces.