撞車鈦痕計算

先將架車加速到不同速度再刹停，量度呔痕長度，以計算該車的減速度。可以用的公式為 v2 - u2 = 2as
之後就可以相同公式，憑得出的減速度及呔痕長度計算當時車速。

Simply speaking, the relevant equation is
v^2 = u^2 + 2.a.s
where u and v are the initial and final velocities of the car respectively
a is the decceleration of the car and s is the distance covered under decceleration.

Since v is equal to 0 m/s, and a is negative for decceleration, the equation then simplifies to
u^2 = 2.a.s

Measuring the skidding mark would give the value for s.

To find a, the relevant equation is
Ff = m.a
where Ff is the frictional force acting on the typres
m is the mass of the car

But Ff = b.mg (assume on a level road)
where b is the coefficient of frcition between the road and typre
g is the acceleration due to gravity

thus, b.mg = m.a
i.e. a = b.g

It is often seen that polce officers investigating the accident would do a re-construction of the accident scenario (意外重組) using the car involved in the accident on the spot of the road where the accident occured on similar weather and road conditions to determine the coefficient of friction of the road.

Once the coefficient of friction is found, the speed of the car invloved in the accident can be found from,

u^2 = 2.(bg).s
or u = square-root[2.b.g.s]