Understanding particle motion in force fields (PMFF), which encompasses the nature of forces and the relationship between force and motion, is fundamental to mastering mechanics and electromagnetism. Effectively solving PMFF-related problems requires advanced reasoning skills and the ability to apply knowledge across diverse contexts. Despite evidence that students often encounter significant challenges with these concepts, comprehensive assessment tools to reliably evaluate their understanding remain limited. In high school and introductory college physics courses, the most commonly studied force fields include those generated by a point mass or a point charge, as well as uniform gravitational, electric, and magnetic fields. The basic types of motion observed in these fields include uniform linear motion, uniformly accelerated rectilinear motion, uniformly accelerated curvilinear motion, and uniform circular motion. This study developed a nine-item multiple-choice test designed to assess students' understanding of PMFF concepts. Data were collected from 34 college physics majors using test scores, interviews, and eye-tracking technology. The analysis revealed several alternative conceptions that varied depending on the specific force field context. Students performed relatively well in uniform force field scenarios but faced significant difficulties with fields generated by a point mass or a point charge, as well as uniform magnetic fields. In fields of a point mass or point charge, common misconceptions centered on uniformly accelerated motion. In the uniform magnetic field context, students often struggled to differentiate between uniform linear motion and uniformly accelerated curvilinear motion. Eye-tracking data provided additional insights, revealing attention patterns that corroborated the observed difficulties. These findings highlight critical areas where students face challenges in understanding PMFF. The results can guide future research efforts to develop targeted educational interventions aimed at addressing these specific learning difficulties, ultimately improving student comprehension of PMFF concepts.