This chapter introduces the fundamental principles of dynamics by exploring what causes changes in motion, moving beyond the simple description of speed and position to identify force as the underlying driver. Defined as a physical quantity with both magnitude and direction, force is measured in newtons (N) and can alter an object’s velocity, orientation, or physical shape. The source distinguishes between balanced forces, which maintain an object’s current state of rest or uniform motion, and unbalanced forces, which create a net force that results in acceleration. Through practical examples like squeezing a lemon or playing tug of war, and scientific milestones like Newton’s first law of motion, the text explains that objects possess inertia, a natural resistance to changing their state unless compelled by an external influence. Ultimately, the material serves as a foundational guide to understanding how various interactions, including friction and gravity, combine to dictate the behavior of everything from a sliding coin to a moving vehicle.