Dynamics is an area of the mechanics. Mechanics is the study of forces acting on a body.  A physical body can be at rest or it could be in motion.  Dynamics is the study of the physical body where the forces are not in equilibrium. Due to this there will be an acceleration on that body.  If the body is at rest, or has constant velocity, all applied forces will be in equilibrium.  If the forces are in equilibrium you would use Statics to solve the problem.

There are two parts of Dynamics. The first part is kinematics, which studies the geometric aspect of motion. The second part is kinetics, which studies the forces that are responsible for the motion.  Additional articles will further discuss these areas.

The study of Dynamics began when it was possible to produce and accurate measurement of time.  Galileo was one of the first physicist to contribute to the field of dynamics. His contributions came from his studies of pendulums and falling bodies.  Isaac Newton was also major contributor to the field of Dynamics when he created the three laws of motion.

Newton’s Laws of Motion
  1. “Every object in state of uniform motion tends to remain in that state of motion unless an external force is applied to it.”
  2. “The relation between an object’s mass m, its acceleration a, and the applied force F is F=ma, where acceleration and force are vectors, and the direction of the force vector is the in the same direction as the acceleration vector.”
  3. “For every action there is an equal and opposite reaction.”

Galileo’s concepts of inertia helped develop the first law. The first law of motion is also known as the “Law of Inertia”.  A perfect example of this would be an object in outer space.  Any object in space will continue to move at a constant speed. Only a force will cause a bodies velocity to change.

One of the most important laws of motion is the second law. The second law will allow you to determine resultant forces caused by an acceleration.  This law is the basis of Kinetics.

Finally, the third law states that if an object acts on another object than its action on that object will have an equal and opposite reaction on itself.  An example of this would be when you step of a boat onto a dock. As you step off the boat it will move away from you as you move towards the dock.

So why is dynamics important to a mechanical engineer?  It is important because most mechanical systems have motion. Due to this fact there are chances of acceleration which would cause a force.  Those dynamic forces can in turn cause stresses on the object.  They can also upset the balance of the object.  Because of this it is important for a mechanical engineer to have firm understanding of Dynamics.

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