Mechanics is the study of motion and the physical interactions that change it. A moving object is an object that is changing its position with respect to something which is fixed. e.g. a car on a road is said to be moving if it changes its position every second with respect to the road. It is easy to tell if something is moving or not, provided we have a set of coordinate axes and a reference point (the origin); comprising what is called a Reference Frame.

However, depending on the forces acting on a body, it can show a number of patterns of movements. e.g. a wheel rolling on an inclined plane shows two kinds of motions, rotation around its axis and moving down towards the ground.

wheel rolling

It gets complicated further if you put an ant on the wheel. that ant, will move all over the wheel, in any direction it pleases, yet will roll down with the wheel. The absolute paths of the ant and the wheel are very complex.

In order to understand this type of complicated motion, you’ll need to separate the different kinds of motions involved, like the rotation of the wheel, its movement down the slope and the path of the ant on it. In order to analyze a problem dealing with motion, you have to analyze the different kinds of motion separately, otherwise it gets very complicated.

The different kinds of motion most commonly encountered in Classical Mechanics are:

  1. Rectilinear motion: motion along a straight line, simplest case of translational motion.
  2. Translational motion: motion in 3 dimensional space such that the path consists of smaller straight line segments.
  3. Simple harmonic motion/oscillation: a particle moves to and fro from its mean position
  4. Rotational motion: a solid body rotates around its own axis
  5. Uniform Circular Motion: a particle moves in a circle around a point, maintaining a constant distance from it
  6. Curvilinear Motion: motion along a curve in space
  7. Random motion: No fixed trajectory/path: possibly a combination of some of the above.

We shall begin by examining the simplest motion of all: Translational motion. For that, we first need to understand the concepts of displacement, speed, velocity and acceleration.

Mechanics: motion and its types
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