Sand Pile Escape Ramp
A sand pile escape ramp is loose rows of sand placed
perpendicular across the ramp that runaway trucks will collide
with. This collision causes the sand to be displaced, which by
Newton's Second and Third Laws leads to the truck's force being
transferred into the sand. There is also rolling friction taking
place.
Hawthorn, Billy. "Runaway Truck Ramp East of Asheville, NC." Wikipedia. Wikimedia Foundation, 23 July 2012. Web. 18 Apr. 2017.
The Physics
The sand piles create rolling friction in
addition to rubbing friction of the sand against the body of
the truck to quickly slow any runaway vehicle. Also, any
truck plowing through the piles will transfer some of their
energy into moving the sand.
This free body diagram shows the forces acting on the truck (left) and the displaced sand (right) along with their respective momentum vectors.
This free body diagram shows the forces acting on the truck (left) and the displaced sand (right) along with their respective momentum vectors.
By the conservation of energy principle, any
energy lost by the truck must be gained in some other way.
This principle combined with Newton's second law is why the
displacement of the sand piles can have a large impact in
slowing down the truck; as the sand is sent flying away at
high speeds, an equal and opposite force acts against the
truck. This in turn reduces the truck's kinetic energy,
which means its velocity.
This relation can be shown in the equation:
Since the truck's mass is constant, any energy lost to the sand will be translated directly to its velocity.
This relation can be shown in the equation:
KE=1/2mv^2
Since the truck's mass is constant, any energy lost to the sand will be translated directly to its velocity.