Car Collisions
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http://www.inkity.com/catalog/product/2/8527/Car-Collision.html
To explain how these
concepts relate in car collisions lets take a look first at
force and how much is needed to stop a car in a distance of
100 meters.
A 2003 Kia Spectra
weighs 2,718 lbs which would give us 1232.864 kg
so
mass (m)= 1232.9 kg
If the Kia was driving at 45 mph which is
approximately 72 km/h.
initial V0=
20 m/s
To find force we will use Newton's 2nd
law: F=ma
we know the mass already but we need to find acceleration
and we can do so by rearranging a the kinematics equation:
v²= v0²+ 2a (x-x0)
to a= v²-v0²/2(x-x0)
a= (0)²- (20 m/s)²/
2(100m) = - 2m/s²
Then we can use Newton's second law to
find the force:
F=ma=(1232.9 kg)(2m/s)= 2465.8 N to stop the
car
The momentum of the Kia
traveling at 45 mph is:
P=m*v= (1232.9 kg)(20 m/s) = 24658 kg*m/s or 2.5 x 10^4
kg*m/s
This is important because the total
change in momentum is equal to the impulse.
Impulse= F * the
change in time
If the Kia had the same impulse but came to 0 m/s in a
shorter amount of time the force would be much higher
than if it took a longer amount of time to reach 0 m/s.
Crumple zones in cars are used for
this very reason. They help to slow down the rate of change
in momentum of the car thus lowering the impact force on the
passenger. Seat belts are also used to lower the force
exerted on the passenger by changing the time of impact.
http://www.aip.org/dbis/stories/2004/14124.html