EasyPhysicsHigh School (11–12)Mechanics › Fluid Flow, Bernoulli's Principle and ViscosityConceptualBoard Exam

Answer, and give a reason. Why do big hailstones hit the ground much harder than small ones? …

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

Answer, and give a reason.

Why do big hailstones hit the ground much harder than small ones?
Why is honey warmed before it is poured?
Why does dust stay in the air of a room for hours?

Need a reminder? The key ideaShow

Viscosity: the force to slide a plate of area $A$ at speed $v$ over a film of thickness $d$ is $F = \eta A\dfrac{v}{d}$ . Stokes' law: a small sphere feels $6\pi\eta rv$ , so it falls at a terminal speed $v_t = \dfrac{2r^2(\rho - \sigma)g}{9\eta}$ .

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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