: How the highest mountain and lowest valley would be X metres apart is used when explaining how round something is.
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What? Could you articulate this better please
That’d be the smoothness of a sphere. Often compared is a billiard ball vs earth, for example.
I think you’re talking about imperfections on a spherical object, right?
Every spherical object has some imperfections, some bits are higher than they should be to be a perfectly round, and some are lower. To put these imperfections into perspective for an everyday person, the earth comparison is sometimes used.
They scale up the object in question and pretend it’s earth-sized, then compare the imperfections to earthly features such as mountains and valleys. So a dip that’s 1mm too low on a ball bearing could be compared to a valley that’s 1000m deep if the bearing were earth sized. (You’d have to work out how much bigger the earth is compared to the object and scale the imperfection size accordingly)
Side-note: Earth isn’t actually a proper sphere and is actually a bit squished along the horizontal axis, but they ignore that fact for this comparison as most people don’t know that.
The average distance to the center of the plane is about 6,371 km
The highest mountain (Everest) is 8.848 km tall.
The shore of the Dead sea is about 0.43 km below sea level.
The deepest point of the Marianna trench the sea is about 11 km below sea level.
If you look at these numbers you see that the deepest trenches and the deepest mountains are basically nothing compared to the size of the earth.
The difference from the peaks of the tallest mountain to the deepest trenches is only about a third of a percent of the earth’s radius.
If you reduced the planet to something human sized the difference in height would be reduced to mere millimeters.
That is very smooth.
Of course the earth is not perfectly round.
But the thing you would notice first if it were reduced to sizes that you can observer would be ever so slightly elliptic. the distance from pole to pole is about 40km shorter than from one point on th equator to its antipode.
40 km is not nothing especially compared to the size of mountains and valleys here on earth but it is still a tiny fraction only of the size of the planet.
By all measures the world is an incredibly smooth and regular sphere of molten rock with a rather thing but incredibly even crust of solid stone with a slightly damp surface.
Its not about roundness its about smoothness. Roundness is measured how much a ball deviates from a perfect sphere. So whether its wider in one dimension than the other. When you want to know how smooth a surface is you look at the difference between the to extremes. By telling a manufacturer that any surface roughness on a pool ball has to be between +5 microns and -5 microns it means that every bump or cracks has to fall between the limits. By giving the limits of how high bumps can be and how deep cracks can be you unequivocally define the smoothness of an object.
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