Molecular motor
Molecular motors are natural (biological) or artificial molecular machines that are the essential agents of movement in living organisms. In general terms, a motor is a device that consumes energy in one form and converts it into motion or mechanical work; for example, many protein-based molecular motors harness the chemical free energy released by the hydrolysis of ATP in order to perform mechanical work. In terms of energetic efficiency, this type of motor can be superior to currently available man-made motors. One important difference between molecular motors and macroscopic motors is that molecular motors operate in  the thermal bath, an environment in which the fluctuations due to thermal noise are significant. Examples. Some examples of biologically important molecular motors: Organelle and vesicle transport. There are two major families of molecular motors that transport organelles throughout the cell. These families include the dynein family and the kinesin family. Both have very different structures from one another and different ways of achieving a similar goal of moving organelles around the cell. These distances, though only few micrometers, are all preplanned out using microtubules. Theoretical considerations. Because the motor events are stochastic, molecular motors are often modeled with the  Fokker–Planck equation or with Monte Carlo methods. These theoretical models are especially useful when treating the molecular motor as a Brownian motor. Experimental observation. In experimental biophysics, the activity of molecular motors is observed with many different experimental approaches, among them: Many more techniques are also used. As new technologies and methods are developed, it is expected that knowledge of naturally occurring molecular motors will be helpful in constructing synthetic nanoscale motors. Non-biological. Recently, chemists and those involved in nanotechnology have begun to explore the possibility of creating molecular motors "de novo." These synthetic molecular motors currently suffer  many limitations that confine their use to the research laboratory. However, many of these limitations may be overcome as our understanding of chemistry and physics at the nanoscale increases. One step toward understanding nanoscale dynamics was made with the study of catalyst diffusion in the Grubb's catalyst system. Other systems like the nanocars, while not technically motors, are also illustrative of recent efforts towards synthetic nanoscale motors. Other non-reacting molecules can also behave as motors. This has been demonstrated by using dye molecules that move directionally in gradients of polymer solution through favorable hydrophobic interactions. Another recent study  has shown that dye molecules, hard and soft colloidal particles are able to move through gradient of polymer solution through excluded volume effects.