Final answer:
Things move at different rates between depths due to factors like medium density, concentration gradient, and molecular mass. Sound waves are faster in denser mediums, while small particles have a constant terminal velocity unless propelled by biological means. Perception of distance can also be affected in mirrors and water due to reflection and refraction.
Step-by-step explanation:
The rate at which things move through different mediums can vary due to factors such as the density of the medium, the temperature, and the mass of the molecules diffusing. For instance, sound waves travel faster in solids than in liquids, and faster in liquids than in air, because the particles in solids are packed tighter together than in liquids, and in liquids tighter than in air. Similarly, the extent of the concentration gradient affects how rapidly substances diffuse, with a greater difference in concentration leading to a more rapid diffusion. Particles with less mass also diffuse faster than heavier ones.
Moreover, the concept of terminal velocity explains why some small particles like microorganisms, pollen, and dust have a constant falling speed in a medium: they settle slowly due to their small size and the resistance of the medium. Sediment in a lake, for example, has a terminal velocity of about 5 μm/s, thus it takes a long time to settle. In contrast, some bacteria can move faster by employing flagella to propel themselves through their environment.
It's also important to understand that these properties impact not only physical movement but also how we perceive things. For example, objects in convex mirrors such as car side mirrors appear closer than they are due to how light reflects off these surfaces. Similarly, the clarity and refraction in water can make mountain streams appear shallower than they actually are.