Question

The cause of floating clouds in the atmosphere is:
$$\left(A\right)$$ Low viscosity.
$\left(B\right)$ Low temperature.
$\left(C\right)$ Low pressure.
$\left(D\right)$ Low density.

Answer 1

Hint: Clouds are composed primarily of little water droplets and, if it's cold enough, ice crystals. The overwhelming majority of clouds you see contain droplets and/or crystals that are too little to own any considerable fall speed. Therefore the particles still float with the encompassing air.

Complete step by step solution:
For an analogy nearer to the bottom, think about small mud particles that, once viewed against a shaft of daylight, seem to float within the air. Indeed, the distance from the middle of a typical water drop to its edge-its radius-ranges from some microns (thousandths of a millimeter) to some tens of microns (ice crystals are typically a bit larger). And therefore the speed with which any object falls is expounded to its mass and surface area-which is why a feather falls additional slowly than a stone of identical weight.
Therefore, we can say that the low density is the cause of floating clouds in the air.
For roughly spherical particles, mass is proportional to the radius cubed; the
downward-facing extent of such a particle is proportional to the $r^2$. Thus, as a small water drop grows, its mass becomes additional necessary than its form and therefore the droplet falls quicker. Even an outsized droplet having a radius of a hundred microns incorporates a fall rate of solely regarding $27cm/s$.
And since ice crystals have additional irregular shapes, their fall velocities are comparatively smaller. Upward vertical motions, or updrafts, within the atmosphere conjointly contribute to the floating look of clouds by compensating the tiny fall velocities of their constituent particles. Clouds typically kind, survive and grow in the air that's moving upward. Rising air expands because the pressure thereon decreases, which grows into thinner, high-altitude air causes cooling. Enough cooling eventually makes vapor condense, which contributes to the survival and growth of the clouds. Stratiform clouds (those manufacturing steady rain) generally kind in an atmosphere with widespread however weak upward motion; convective clouds (those inflicting showers and thunderstorms) are related to updrafts that exceed some meters per second. In each case, though, the atmospherical ascent is decent to negate the tiny fall velocities of cloud particles. Another way let's say the relative lightness of clouds is to check the full mass of a cloud to the mass of the air during which it resides. Contemplate a theoretical however typical little cloud at associate degree altitude of $10,000$ feet, comprising one metric capacity unit and having a liquid water content of $1g/m^3$.

Note: The full mass of the cloud particles is regarding one million kilograms that are roughly akin to the burden of five hundred cars. However, the full mass of the air therein the same metric capacity unit is regarding one billion kilograms—one thousand times heavier than the liquid! So, even supposing typical clouds do contain heaps of water, this water is spread out for miles within the sort of small water droplets or crystals that are therefore little that the result of gravity on them is negligible. Thus, from our vantage on the ground, clouds appear to float within the sky.