Which branch refers to the study of a rigid body in motion under the action of forces?

• A. Statics
• B. Kinematics
• C. Strength of Materials
• D. Dynamics

Answer: (D)

Dynamics is the study of a rigid body in motion under the action of forces. It analyzes how external forces cause translational motion (described by F = ma) and how forces and torques cause rotational motion (described by τ = Iα). This contrasts with statics, which looks at bodies in equilibrium with no acceleration, and kinematics, which describes motion—positions, speeds, and accelerations—without regard to what forces cause it. Strength of Materials deals with how materials deform under loads, not the motion of bodies. So the branch in question is dynamics because it connects forces to the resulting motion of the body.