SAFETY OF CAR AND
PHYSICS
(HOW THINGS WORK?)
Seung-Jae You
Sunghun Jun
Which parts of the car
protects the driver from
accident?
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1. Tires ( Automobiles Tires and Friction)
2. Seatbelt ( Seatbelt and Inertia)
3. Airbag ( Airbag and Momentum & Impulse)
4. Crumple Zone (Crumple zone and Newton’s
Law)
Automobiles Tires &
Friction
 The friction between the tires of an
automobile and the road determine the
maximum acceleration.
 However, more importantly, it determines
the minimum stopping distance
 The nature of the friction could actually be a
matter of life and death.
 As a result, more friction, more safe
Automobiles Tires &
Friction
 How can we increase the friction?
- Increase the coefficient of friction
- If the surface of tire is rougher, then the friction
force is larger
- When a tire contacts dry asphalt ground, the
coefficient of friction increases.
- On the other hand, if the roads are wet, a tire
contacts with water, the coefficient of friction
decreases
- ex) hydroplaning
Automobiles Tires &
Friction
 Various types of tires

This is an all-season tire. The grooves provide a way for water
to escape, increasing the coefficient of friction. The grooves
are small enough to prevent the bumpy ride of the next tire

The wide deep grooves here allow snow and mud to
penetrate. But they give a noisy bumpy ride on pavement ...
and if the treads get clogged with mud, the treaded tire
essentially becomes a mud-covered 'slick' with a low
coefficient of friction
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In extreme mud, these tractor or bush tires can transfer more
force, but the mud doesn't get caught in tiny grooves, so they
retain their traction
Automobiles Tires &
Friction
Seatbelt and Inertia
 Newton’s 1st law: an object will move with
constant speed in a straight line except when
acted upon by a net force
 when a driver stops the car suddenly, the
driver fall forwards, because the driver’s body
try to maintain its speed.
 Consequently, a seatbelt holds the driver and
prevents the driver from falling forwards
when the car stops
 Seatbelt increases the time of impact
(impulse and momentum) so that it results
lesser impact
Airbag and Momentum &
Impulse

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Every object has momentum.
Momentum consists of a driver’s mass and velocity
- Momentum (p) and Impulse (FDt)
- p = mv, FΔt = mΔv
 There has to be a force in order to stop the driver’s
momentum.
 The driver may hits the dashboard or windshield w
hich also acts as a force stopping the driver but it i
njures them at the same time
 By the way. Airbag gives a force over time (Impulse
). The more the the force acts on the driver to slow
him down, the less damage caused to the driver
Crumple Zone
 It is also known as crash
zone.
 It absorbs energy from a
collision and reduce the
force of a collision.
 Bending during a car crash
increases time to halt the
car.
 Newton’s first and second
laws are applied to
crumple zone.
Newton’s First Law
 Newton’s First Law (The law of inertia.)
 Many people are injured because of the law
of inertia.
 Although the car stops, the person inside
does not stop.
 An unbalance force, crumple zone, lowers the
tendency of people to move forward in car
crash.
Crumple Zone
 Newton’s Second Law
 The second law is expressed in equation form
as F=MA. (F= force, M= mass, A=acceleration)
 A=V/T (V= velocity, T= time)
 More time means less acceleration.
 Less acceleration by increased time reduces
force that applies to people inside of the car.
What new insight does this
topic provide to you
 Many people think tire’s surface guarantee
your safety 100%, but tire’s surface just
makes you safe on the snow, water, or any
other ground.
 Since car body seems easily bend, Some
people think that crumple zone makes the car
less protected.
 However, It is just misconception. In fact,
crumple zone makes car more safe.
What new insight does this
topic provide to you
 A misconception of AWD and 4WD is that
they are safer.
 In fact, they help little bit in cornering and
driving on snow.
 However, it has nothing to do with braking
ability
 AWD and 4WD do not provide additional
ability for steering
 AWD and 4WD do not provide additional
ability for braking.
What new insight does this
topic provide to you
 Even if the car’s safety improve, this is what
happen if you drive too fast
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references and bibliography
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http://auto.howstuffworks.com/under-the-hood/car-part-longevity/brake-padslast1.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/frictire.html
http://www.worsleyschool.net/science/files/tires/andfriction.html
http://tristanmac.tripod.com/id14.html
http://tristanmac.tripod.com/id8.html
http://autofyz6.wordpress.com/2008/04/23/the-physics-of-seat-belts/\
http://hyperphysics.phyastr.gsu.edu/hbase/seatb.htmlhttp://web.cvcaroyals.org/~rheckathorn/docum
ents/PhysicsofCarCrashesteachersguide.pdf
http://www.wheelsnext.com/content/tire_cornering.html
http://consumerguideauto.howstuffworks.com/your-ride-4wd-vs-awdcga.htm
http://www.physicsclassroom.com/class/newtlaws/u2l3a.cfm
http://www.toledotechnologyacademy.org/Documents/PhySci%20Docs/Enr
ich2-3.pdf
http://www.gcsescience.com/pfm46.html