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Lincoln leaflet: Physics - image description

[Left box]

Motor vehicle crashes in New Zealand 2010

During the 2010 calendar year there were:

337 fatal road crashes

10,549 injury crashes

375 casualty deaths

14,031 casualty injuries

[Right box]

Newton's first law

"In the absence of external forces, an object at rest remains at rest and an object in motion remains in motion with a constant velocity."

So when you're travelling in a car and you hit an object, the car stops but you keep going. This results in you flying out of your seat into the seat in front of you, or even out the window. This also applies to your brain. When you stop, your skull stops. But your brain keeps moving and hits the walls of your skull. This can result in brain damage.

Newton's second law

"The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass."

This can be represented in the equation "F= ma" which means force equals mass times acceleration. If used in the situation of a car accident, this means the faster you drive, the higher the force you hit the object with, resulting in a larger crash.


Seat belts and airbags do more than prevent you flying out of your seat; they also spread the deceleration of your body over a larger area. Deceleration itself doesn't harm a person. The deceleration in a short period of time will do harm. Airbags are designed to slow the body so the deceleration is spaced over a longer time period.

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Published on: 11 Oct 2012