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The white colour of clouds is due to Mie scattering. This arises because the refractive index of water is different from air. If the particles are large enough all wavelengths are scattered equally so there is no change in the colour of the scattered light. This is the case in clouds where droplet sizes are typically 10 to 20 microns. The light scattering ...

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Consider a continuous body $C$ and a closed subset $V$ with boundary $\partial V$ completely included in $C$ (notice that $\partial V \subset V$). If $p \in \partial V$, the external part of $C$, namely $C \setminus V$ acts on $p$ (actually on a neighbourhood of $p$ in $\partial V$) by means of a superficial force d\vec{f} = \vec{s}(p, \vec{n}) ...

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The hydrostatic pressure is one-third of the trace of the stress tensor. In other words, the pressure is the average of the normal stresses on a given volume. If you are using equations that include both pressure and a stress tensor, care must be taken to make sure that the diagonal components of the stress tensor don't also include the pressure terms. ...

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We have observed that the underlying level of nature is quantum mechanical. Quantum means "a definite quantity" of something so definite quantities can be counted and so integral numbers play a role : a) in the number of particles , in the number of energy levels characterized by quantum numbers ( i.e. integer numbers).b) There are the fields which are ...

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Generally speaking, particles are quantized: you have $0,1,2,3,4\dots$ of them. Even in quantum mechanics, you may not know how many you have, but if you measure it you will get a natural number. Most other quantities are real numbers and can take any real value. It is very hard to say why-some would say that is the definition of a particle.

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