Kinematics is the study of the motion of mechanical points, bodies and systems without consideration of their associated physical properties and the forces acting on them. The study is often referred to as the geometry of motion, and it models these motions mathematically using algebra.
The systems in kinematics are modeled to calculate such things as speeds and ratios. An example model of bodies in a system is the gears in a vehicle’s transmission. These models are used to engineer all manner of mechanical devices and to model the motions of existing physical bodies, including the motion-rigid, body-hinged mechanics of the human skeleton or the motion of celestial bodies in astrophysics, which is also known as stellar kinematics.
Kinematics is very useful in the conceptual design of mechanical systems. Initial geometries and velocities of bodies are a part of the model. While kinematics can help determine whether a design is theoretically possible, there are more complexities when designing something for the real world. Without consideration of materials, and the forces acting upon them, many theoretically possible designs would be prone to failure.
Kinetics, in contrast to kinematics, does consider physical properties such as the mass of the bodies or the forces driving them. Kinetics is logically deduced from kinematics by way of algebraic calculation of physical properties and forces. Kinetics takes into account physical forces and properties including material properties, like mass rigidity, and tensile or compressive strength. These properties, coupled with physics and thermodynamics, can take a theoretical model from kinematics and help determine how to engineer a viable, reliable and functioning real-world system.