Physics recognizes three forms of motion. Uniform motion refers to location changes at a constant speed. For example, a train traveling from station A to station B at a constant speed of 50 mph. Accelerated motion refers to location changes that involve acceleration. For example, when an apple falls from a tree, it accelerates due to the force of gravity. Random motion refers to changes in location that are random, unexpected or unpredictable. An example of random motion is the movement of sub-atomic particles. Within these forms of motion, there are four basic types of motion: translatory, rotatory, vibratory and Brownian.
Translatory motion refers to an object moving from one point to another. This type of motion can be further broken down into rectilinear and curvilinear motion. Rectilinear motion is a change in location that follows a linear path, and whose displacement is exactly the same as its trajectory. Displacement is simply the shortest distance between the object’s starting point and final position. All linear motions are one-dimensional. Curvilinear motion is a change in location that follows a curved path. This is a compound, or two-dimensional movement. An example of curvilinear motion is the trajectory of a canon ball.
Rotatory motion refers to an object that remains in one location, while spinning about an axis. However, some sources consider both rotation around an internal axis, such as with the spin of the earth, and around an external axis, such as the earth’s orbit around the sun, as rotatory motion. In this case, what distinguishes rotatory motion from curvilinear motion is that the object will return to its original starting point, having completed a rotation. Others consider rotation around an external axis to simply be a form of two-dimensional, curvilinear motion.
Vibratory motion, also referred to as oscillatory, refers to a back and forth motion, within a mean position. This type of motion includes vibrations and harmonic motion, such as a pendulum or swing. The boundaries of this motion are referred to as the extreme points.
First observed in 1827 by Robert Brown, this type of motion is an erratic and constant movement of tiny particles when suspended in a fluid or gas. This motion is three-dimensional. Albert Einstein devised a mathematical explanation for this motion in 1905, integrating it into his kinetic theory. This motion is actual a random series of rectilinear motions, caused by the collision of molecules with the particle, and is often not included as one of the three primary types of motion. Brownian motion can also create rotatory motion in the particles.
There is another form of motion, called wave motion. This type of motion involves the translation of energy, not a physical object. For instance, when a tsunami crosses an ocean, it is the energy that moves and not the water molecules themselves. The energy is transferred from molecule to molecule, allowing for far greater speeds. Wave motion can be broken down into longitudinal and transverse motion.