Level 6: Friction and slopes

Forces and motion · level 6 of 8 · rough age 13-14 (a guide for parents; anyone can start anywhere)

In this level friction gets numbers. You meet static and kinetic friction and the coefficient of friction, split the weight of something on a ramp into two parts, and work out when it slides and how fast. Then come two surprises from Mars: whether a parked rover slips on a slope does not depend on gravity at all, and nor, nearly, does the steepest slope a sand dune can hold.

Lesson	You will be able to
Static and kinetic friction	Explain the two kinds of friction and why it is harder to start a slide than to keep one going
The coefficient of friction	Use \(F \le \mu N\) to find friction forces on Mars and on Earth
Forces on a ramp	Split weight into parts along and across a slope
Sliding down a ramp	Find the acceleration of something sliding down a slope, with friction
Parked on a Mars slope	Show that the angle at which something slips does not depend on \(g\), and find it
Sand piles and dunes	Explain the angle of repose and why Mars dunes are about as steep as Earth's

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