Brain responses due to its movability during impact was investigated by using sliding interface approach. A new 3D 50th percentile human head finite element model has been generated in which sliding interfaces totally separate the brains and cerebrospinal fluid (CSF)/cranium. So, the brains can move to some extent. It becomes an equivalent one to most widely used brain/CSF (cranium) coupled models by switching interface type from sliding to tied. The model was partially validated by using available experimental and computed data in frontal impact. Compared with brain/CSF (cranium) coupled models, the new model predicts higher brain stress levels at sites such as corpus callosum, brain stem, and the vicinity of the ventricles etc. and more realistic deformation patterns. The results suggest that a fluid-solid interaction approach should be used to better model brain movement during impact to correctly interpret the brain injuries and to evaluate proposed head injury mechanisms.