Newton's Laws and Car Safety
Newton's Laws
Isaac Newton’s Laws of Motion describe how forces change the motion of an object, how the force of gravity
gives weight to all masses, how forces cause acceleration and how forces work in collisions.
Car safety features
Newton's Laws are very important when it comes to car safety.
When there is a car crash, the car, its contents and the passengers decelerate rapidly. They
experience great forces because of the very large deceleration, which can cause injury.
Modern cars also have safety features that absorb kinetic energy in collisions. These typically include:
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seat belts
air bags
crumple zones
These features increase the time taken for the change in speed of the occupants. This reduces the
deceleration, which causes the forces involved to be reduced, and consequently serious injuries to be
reduced.
Seat belts
Seat belts stop you tumbling around inside the car if there is a collision. Upon sensing a collision the
seat belts lock in place. When the car crashes, there is no unbalanced force acting on the person, so
they continue forward (Newton's First Law). The person moves against the seat belt, exerting a force
on it. The seat belt then exerts a force back on the person (Newton's Third Law). This causes a
controlled deceleration of the person.
Why Cars Have Seat Belts
When your car accelerates, the car seat supplies the force required to accelerate you along with it.
The heavier you are and the faster the car accelerates, the stronger this force needs to be. When the
car stops, you keep right on going until something supplies a force in the opposite direction to stop
you. Your legs can supply this force if the cars slows down gradually, but if the car hits an obstacle,
the deceleration and force are too much for your legs or arms to handle.
Air bags
Air bags increase the time taken for the motion of a car occupant's head to decelerate from maximum
speed to zero. A short sharp deceleration would involve a very large force, increasing the chance of a
head injury. A longer time slowing down decreases deceleration thereby reducing the size of the force
acting and decreasing the chance of injury.
Crumple zones
Crumple zones are areas of a vehicle that are designed to crush in a controlled way in a collision.
They increase the time taken for the vehicle to slow down in an impact (like an airbag). This reduces
the force exerted on the passengers. The deformation (crumpling) of the car also absorbs energy
from the collision meaning that less energy is transferred to the passengers.
The Force of a Collision
The force required to stop a 68-kilogram (150-pound) person traveling at 26.8 meters per second (60
miles per hour) in 5 seconds is 364 newtons (1,800 pounds). If the car hits an obstacle and stops
suddenly, that force goes up to 1,822 newtons (9,000 pounds). In the absence of seat belts, the force
is supplied by the windshield or steering wheel, and the impact is more than enough to kill the person.
Driving safely
The above safety features are there to reduce the chance of injury when an accident occurs. Ideally
responsible drivers should do the following to decrease the chance of an accident.
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Not exceed the speed limit (greater speed = greater kinetic energy = greater chance of injury in an
accident).
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Pay careful attention to other road users.
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Obey the Highway Code.
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Refrain from using mobile phones/ipods while driving which take driver's concentration away from
driving carefully.
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Drive to the conditions of the road – the speed limit might be 30 mph but in icy conditions the stopping
distance will be increased.
Write a 5-7 paragraph 500 word essay that describes how
Newton’s Laws work with Car Safety