The mysterious sliding stones . Along the remote Racetrack Playa in Death Valley
ID: 1354011 • Letter: T
Question
The mysterious sliding stones. Along the remote Racetrack Playa in Death Valley, California, stones sometimes gouge out prominent trails in the desert floor, as if the stones had been migrating (see the figure). For years curiosity mounted about why the stones moved. One explanation was that strong winds during occasional rainstorms would drag the rough stones over ground softened by rain. When the desert dried out, the trails behind the stones were hard-baked in place. According to measurements, the coefficient of kinetic friction between the stones and the wet playa ground is about 0.84.
Explanation / Answer
Force = mu*N
N = 9.8 m/s/s* 21kg
mu = .84
Force = 0.84*9.8*21 =172.8 Newtons or aprox 173 Newtons