Engineering Expert Witness Blog

     Last week we talked about one of the ten core disciplines of mechanical engineering, statics.  Today our focus will shift to a discussion of how mechanical engineers use the study of Dynamics to solve problems.  As its name implies, Dynamics involves the study of how things change, or more specifically, how they move.  Dynamics can be broken down into two basic parts:  kinematics and kinetics.  We’ll focus on kinematics this week.

     Kinematics is the study of the geometry of motion.  Kinematics is used to develop a relationship between how far an object travels in a given time, its velocity, and its acceleration.  The precipitating cause of the motion is not considered in kinematics.

     Before beginning our discussion of kinematics, let’s go back to the good ol’ days and revisit what should be some very familiar ground to anyone who’s taken algebra.  Does this word problem sound familiar to you:  If you start at point X and you’re going at Y speed for a given length of time, T, what distance will you have traveled?

     Here’s the same problem presented in another way.  Suppose you’re driving and you set your cruise control at 70 miles per hour.  Out of curiosity you want to know how far your automobile will travel in 15 minutes (0.25 hours).  Kinematics teaches that the relationship between velocity, time, and distance can be demonstrated by this equation:

Distance = (Velocity) x (Travel Time)

Distance = (70 miles/hour) x (0.25 hour) = 17.5 miles

     Of course kinematics can get far more complicated than this simple example, especially when objects accelerate, decelerate, change direction, and move in paths that are nonlinear, that is, not in a straight line.  

     Next week we’ll talk about the study of kinetics, particularly Sir Isaac Newton’s Second Law of Motion.

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