Professor Ramamurti Shankar: For a photon I told For any particle the square root of its momentum is really the square root of its mass times c2.
A photon is a particle whose square of the four-momentum is 0. Material particles that can come to rest have a square of the fourth momentum, which is m2c2.
The extremely rare charged particles strike Earth at a rate of one particle per square kilometer per century.
When the NTSB, in collaboration with Fokker, investigated the effect ice can have on an aircraft, they found that ice particles as small as 1-2mm of a density of one particle per square centimeter can cause a loss of lift of over 20%.
Below the nm scale, normal diffusion is guided by Brownian motion and results in particle mean square displacements that increase linearly with time, while diffusion coefficients decrease with hydrodynamic forces.
At one point, they found 466,000 particles per square kilometer, with an average of 43,000 particles per square kilometer.
Research conducted in 2013 by the State University of New York found that the lakes were riddled with microbeads, with Lake Ontario containing an estimated 1.1m plastic particles per square kilometer.
The group drags finely meshed netting along the lake surfaces, harvesting tens of thousands of particles per square mile, and studies them with microscopes.
A 1943 civic survey found that 1,400 tons of smoke particles per square mile were falling on Bilston each year, which local historian Frank Sharman colourfully suggests is "roughly the weight of 11 blue whales or 233 elephants per annum".
A correlation has been proposed in which the mass flow rate is proportional to D52 multiplied by a factor which is a linear function of particle diameter squared.
