Explaining Newton's Laws of Motion by Examining a Car Accident
According to the National Highway Traffic Safety Administration, there are
over 6 million car crashes each year in the United States. Many of these are
not very serious, while others cause extensive damage and even death. The
cause of an accident can vary from distracted driving to poor road
conditions, but the results of the crash can be explained using physic s.
Isaac Newton's Three Laws of Motion
To understand the effects of a car accident, you first need to understand a core concept discovered by Sir
Isaac Newton. Born on December 25, 1643, he attended the Free Grammar School in England and then
went on to study at Trinity College in Cambridge. In college, he developed an interest in math, physics and
astronomy and graduated with a bachelor's degree in 1665. His attempt to continue his education was
postponed by the plague which caused the college to temporarily shut down and force Newton back home .
In 1666, he was only 23 years old when he first started developing theories related to gravitation. After
Trinity College reopened, Isaac Newton was able to accept a fellowship in order to complete his masters
degree. By 1686, he presented his laws of motion in the Philosophiae Naturalis Principia Mathematica or
Principia. This three book series outlines his following three laws:
1. An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion
continues in motion with the same speed and in the same direction unless acted upon by an
unbalanced force.
2. Acceleration is produced when a force acts on a mass. The greater the mass (of the object being
accelerated) the greater the amount of force needed (to accelerate the object).
3. For every action there is an equal and opposite re-action.
Static and Kinetic Friction
Friction is an important element to understand when examining the physics of a car accident. Fricti on is
simply the force between a surface or object as it moves over another. There are two types of friction,
static and kinetic. Static friction is the force needed to get an object moving from a resting position. You
can think of a car tire on a road. The two objects exert friction against each other and that force must be
overcome to make the tire turn, moving the car. Kinetic friction is the force needed to keep an object in
motion. Using the same example of a tire on a road, there is still friction bet ween the road and tire so to
keep the tire and car moving, additional force must be maintained or else the tire will stop turning and the
car will stop.
Types of Collisions
When mentioning types of collisions, we're not referring to "head on" or "single ve hicle", but rather the
two general types in physics: elastic and inelastic. An elastic collision is one where two objects collide and
then "bounce" apart such as what happens when to rubber balls come into contact with one another. An
inelastic collision is one where the objects collide but do not bounce away from each other. An example of
this is a car ramming into a wall. Certain safety features of automobiles have been created to utilize these
forces such as your bumper. At low speeds, the bumper is designed to bump the object that is impacted
without causing damage. At higher speeds, instead of bumping the object that was hit, the force will
crumple the bumper in order to release some of the energy from the collision.
Effects of Collisions on People
Passengers in a vehicle that is involved in an accident are impacted by several forces. These forces can be
calculated using physics, tested with crash test dummies and computer simulations and integrated into
new safety features.
Crash Tests without Seatbelts
Cars are designed with crumple zones so they may slow down over a longer period of time, which
keeps the force smaller (see impulse). However, this safety feature alone will usually not prevent
serious injury or death to the occupants of a car during an accident. The crumple zone only slows
the car more gradually. The only way it slows the occupants more gradually is if they are attached
to the car. Otherwise, the car may come to rest more slowly but the people come to rest
immediately upon striking the already stopped interior of the car. Stopping in a small amount of
time means the force must be very large.
Passenger Kills Driver and Self
Not wearing a seatbelt not only puts your life in danger but also anyone else who happens to be
riding with you. The force from the seatbelt safely decelerates the driver, but the child in the back
seat follows Newton's Law of Inertia and continues moving in the absence of a net force. The 60
mph "kid" not only breaks its own neck but also the neck of the driver.
Bad Guard Rails
Guard rails are intended to protect people by preventing cars from leaving the sides of the road near
cliffs, rivers, curves, and bridges. Most of the time they do this well. Unfortunately, some older
guard rails actually pose a threat to lives. If the guard rail does not end by being curved to the
ground, or in a breakaway design, the rail may be capable of impaling a moving car and its
occupants. The ends of these older rails are usually sharp and difficult to see from the end. A
rapidly moving car upon running into one is met with a very large force and high pressure as that
force is exerted on a very small edge of the rail. The effect is known as "guard rail spearing".
Crash Tests with Seatbelts
Seatbelts use two main ideas to protect passengers during a car accident. First, they slow the
passenger down more slowly than the passenger running into steering wheel or dashboard. This
keeps the force required to stop them smaller. It also prevents the person from contacting any of the
glass windows in the car or continuing on to be stopped abruptly by the road, tree, or another
automobile. The video clip above shows the role of the seatbelt during an accident.
Write a 5-7 paragraph 500 word essay that describes how
Newton’s Laws work with Collisions.
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