According to the University of Hawaii, mathematicians took a sample in a bowl and calculating the grains of sand in it. Then from that they done the math and worked out how many grains of sand there are in the entire world.
Unlike humans, fires usually travel uphill much faster than downhill. The steeper the slope, the faster the fire travels. Fires travel in the direction of the ambient wind, which usually flows uphill. Additionally, the fire is able to preheat the fuel further up the hill because the smoke and heat
Sound is a type of longitudinal, mechanical wave. They need a medium (the elasticity of the molecules) to propagate and will not travel through a vacuum. Sound travels at different speed in different media. The speed of sound is determined by the density and compressibility of the medium. Density is