How have advances in
technology affected
the safety of
vehicles?
Unit Questions
 What forces act on a car and on the body
during a car crash?
 What are some causes of vehicle crashes?
 What are 3 types of collisions that occur
during a car crash?
 How can vehicles be made safer?
 What can you do to be safe in a vehicle?
Car Crash Physics
By Lisa Atwell
Overview
 Forces acting on your car and body in a car crash
 Physics of moving objects
 Newton’s Laws of Motion
 3 types of collisions that occur during a car crash
 Causes of car crashes
 Vehicle safety
The Physics of Moving Objects
Is how much matter is in something.
The more you stuff in your
suitcase,
the more massive it becomes.
Is how fast
something is
traveling.
Near your school, your
mother presses on the gas
pedal to make the car go 15
mph (miles per hour)
On Interstate 82, your
father presses on the gas
pedal to make the car go 70
mph.
Direction is not important !
is
distance
time
Is how fast
something is going
and
in which direction.
+
is
distance
time
in a
direction
55 mph south
is
the change in
When a car accelerates, it may be speeding
up or slowing down.
Remember:
 Mass is the amount of matter in
something.
 Speed is how fast something is
traveling.
 Velocity is how fast something is
traveling in a direction.
 Acceleration is a change in speed.
Experiment #1
Velocity or
Acceleration?
Newton’s 2nd Law of Motion
F = ma
Force equals mass times acceleration
is a push or a pull.
This law means that while you are applying a force on an
object, it will continue to accelerate or change its
velocity. It also states that the greater the force on
an object, the greater the acceleration.
Do you know the
word that
describes a
in motion ?
Here is a clue:
The Starkville Academy running back is
running toward the goal.
The Heritage linebacker grabs his legs
one yard from the goal line.
The running back can’t move his legs, but still
scores for SA and wins the game!
The announcer says the player’s
carried him over the goal line.
is
in motion !
Momentum = mass x velocity
All objects have mass.
If an object is moving, it has momentum.
Momentum
and its relationship to mass and speed
 Suppose the 150 lb Starkville Academy
running back has a speed of 10 mph going east.
 Suppose the 100 lb Heritage Academy line
backer has a speed of 10 mph going west.
They collide head on at the goal line.
What are the results ?
Momentum = mass x velocity
The Starkville Academy player has a mass of 150
lb and is running 10 mph toward the east.

His momentum is 1500 lb mph east

The Heritage Academy player has a mass of 100
lb and is running 10 mph toward the east.
His momentum is 1000 lb mph west
The result is a final momentum of 500 lb mph east
(towards the goal line).
x
time
the force is applied
A moving car has momentum.
When this car crashes, it’s momentum is changed.
A change in momentum is called an
is an applied
over a period of
time .
.
Remember:
 Mass is how much matter is in something.
 Acceleration is how fast you are changing
your speed.
 Velocity is speed in a direction.
 A force is a push or a pull.
 Momentum is mass in motion.
 Impulse is the force times the time the
force is applied.
Experiment #2
Egg Toss
Stop that egg!
In the car’s collision, the
Determines the amount of damage to
the car and the passengers
Newton’s First Law of Motion
Inertia
Without a push or a pull, an object
at rest remains at rest and an object
in motion remains in motion.
Newton’s 3rd Law of Motion
When object 1 pushes on object 2
with a force
object 2 pushes back on object 1
with the same force
but
in the opposite direction.
What causes vehicle crashes?






Speeding
Too many lane changes
Following too closely
Running red lights
Distractions
Driving while under the influence
Have you ever wondered what happens
inside a car when it crashes?
In each car crash
there are actually three collisions:
The Car's Collision
The Human Collision
The Internal Collision
If the
time to stop a
is
Then the stopping
is
and the
to the car and driver is great.
If the
time to stop a
is
the stopping
is
and the
to car and driver is less.
Car Crash
In a Car's Collision
 During a crash, the car crashes to a stop.
 At 30 mph, a car hitting an object that is not
moving will crumple in about two feet.
 As the car crushes, it absorbs some of the
force of the collision and increases the
stopping time.
More stopping time means
In a
the stopping
time
is
by having a
front end and bumper on the car.
The Human Collision
 At the moment of impact, passengers in the
automobile are still traveling at the vehicle’s
original velocity.
 When the car comes to a complete stop the
passengers continue to be hurled forward until they
come in contact with some part of the automobile
(the steering wheel, the dashboard, the front window or
back of the front seat).
 Humans in a crash can also cause serious
injuries to other humans when they
collide with each other.
 People in the front seat of a car are
often hit by rear-seat passengers as
they fly forward with incredible force.
The Internal Collision
 In a crash, even after a human body
comes to a complete stop, its internal
organs are still moving.
 Suddenly, these internal organs slam
into other organs or the skeletal
system.
 This "internal collision" is what often
causes serious injury or death.
What happens when two objects
collide?
Influences:
 Mass
 Momentum
 Velocity
 Impulse
 Time
 The impulse experienced by the car equals a
change in momentum.
 As car designers, we only have control over
mass and time.
What Helps Drivers and Passengers
Survive Collisions?
 Air Bags
 Seatbelts
 Bumpers
Seatbelts
 Purpose is to restrain passengers from tossing back
and forth after a collision
 Lap belt protects the pelvis and the shoulder belt
protects the rib cage
 Have ability to extend and retract, but in a collision
the belts will suddenly tighten up and hold passengers
in place
Air Bags
 Purpose is to slow down passengers speed
after a crash
 A soft pillow to land against in a crash
 Works within a fraction of a second
Sometimes an air bag
or seatbelt is used to
No airbag
No seatbelt
No seatbelt
with baby
stop the passenger
Hit from
behind
Seat belts
Bumpers
 The bumper’s purpose is to absorb crash energy
without significant damage to the bumper itself and no
damage to the vehicle’s rear or front end.
 Low speed crashes mostly occur in urban traffic.
 Less damage is done in a collision when 2 vehicles are
lined up bumper to bumper.
 Bumpers can protect other components of a vehicle.
But as the driver, please remember,
does kill.
Distance it takes to safely stop a car
Speed
(mph)
Reaction
Time (ft)
Breaking
Distance (ft)
Total
Stopping
Distance (ft)
10
11
6
17
20
22
24
46
50
60.5
181.5
242
65
65
253.5
325
70
77
294
371
Longer than a
football field
How many times have you
heard people say…
 “I don’t need to buckle up.”
 “I am just going around the block.”
 “I was just going 30 mph.”
 While it is true that slower speeds reduce the risk,
don’t forget that seat belt!
 11 percent of all fatal crashes occurred when the
car was going 30 mph or less.
Think of the following scenarios, when you make
that choice to use your seat belt:
At 3 mph
 Imagine that you are hit head-on by a football tackle
running 3 mph. He knocks you flat and your head hits the
turf. You wake up in the hospital with a serious concussion
and a sprained neck.
At 15 mph
 Imagine shoving your face into the windshield or your chest
into the steering wheel at that speed, with no helmet, no
pads, and no chance to brace yourself
At 35 mph
 You are driving at 35 mph when a deer darts in front of
your car. You brake quickly, miss the deer and keep your
car on the road. Shaken up, you pull over. An officer stops
to offer assistance and then issues a citation for not
buckling up. "Next time, you might not be so lucky,” he
says.
At 40 mph
 Suppose you stand on top of a five story building and fall
off head first.
 This represents 40 mph.
Would you jump?
Remember,
More stopping time,
means
less force!!
Experiments
 Bumper Design
Challenge
 Automotive Design
Engineering Challenge
Questions
 What are the three types of collisions that
occur during a car crash?
 What are some causes of car crashes?
 How can you remain safe in a car?
Resources

CAVS Outreach Program, Cuicchi, P., & Cuicchi, R. (n.d.). Mission eggcellence
challenge [Brochure]. (Available from Center for Advanced Vehicular Systems,
Mississippi State University)

Henderson, T. (1996). Lesson 4: Newton’s third law of motion. In The physics classroom
tutorial. Retrieved March 2, 2008, from Glenbrook South High School Web site:
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/newtlaws/u2l4a.html

Henderson, T. (1996). Speed and velocity. In The physics classroom tutorial. Retrieved
March 2, 2008, from Glenbrook South High School Web site:
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1l1d.html

Wirt, S. (1999). The physics zone: Forces, accelerations, and car accidents. Retrieved
March 2, 2008, from Oswego City School District Web site:
http://regentsprep.org/Regents/physics/phys01/accident/default.htm

Zobel, E. (1997). Newton’s second law of motion. Retrieved March 2, 2008, from
http://id.mind.net/~zona/mstm/physics/mechanics/forces/newton/newtonLaw2.html