Density and viscosity are independent

Mercury is 13× denser than water yet flows just as easily; honey is barely denser than water yet far more viscous.

Why it works

Density is about mass per volume; viscosity is about internal friction resisting flow — a fluid can be heavy and thin, or light and thick, with no contradiction.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

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More in Mechanical

• The bolt-torque shortcutTightening torque ≈ 0.2 × preload × bolt diameter (dry steel).
• Torque mostly fights frictionRoughly 90% of tightening torque is lost to friction; only ~10% actually stretches the bolt.
• Deflection limits: span/250Keep beam deflection under span/250 generally, span/360 where people will notice a bouncy floor.
• Depth beats width, cubedDouble a beam’s depth and its deflection drops 8-fold. Double its width and it only halves.

Are denser fluids more viscous?

Mercury is 13× denser than water yet flows just as easily; honey is barely denser than water yet far more viscous. Density is about mass per volume; viscosity is about internal friction resisting flow — a fluid can be heavy and thin, or light and thick, with no contradiction.

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