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 PhysicsBy 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.

Direction is not important !

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.

is

time

distance

Is how fast something is going and in which

direction.

+

is

in adistance

time direction

55 mph south55 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.

Velocity orAcceleration?

Experiment #1

Newton’s 2nd Law of Motion

Force equals mass times acceleration

is a push or a pull.

F = ma

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 !

All objects have mass. If an object is moving, it has momentum.

Momentum = mass x velocity

Momentumand its relationship to mass and speed

Suppose the 150 lb Starkville Academy running back has a speed of 10 mph going east.

They collide head on at the goal line.

What are the results ?

Suppose the 100 lb Heritage Academy line backer has a speed of 10 mph going west.

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).

Momentum = mass x velocity

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 appliedover a period of tim

e

.

.

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 TossStop that egg!

In the car’s collision, the

Determines the amount of damage to the car and the passengers

Inertia

Without a push or a pull, an object at rest remains at rest and an object in motion remains in motion.

Newton’s First Law of 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 butin 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 timeto stop ais

Then the stopping is

and the

to the car and driver is great.

If the time

to stop a

isis

the stopping is

to car and driver is less.

and the

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.

Car CrashCar Crash

More stoppingtime

means

In a

the stopping time

is

by having a

front end and bumper on the car.

The Human Collision

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).

At the moment of impact, passengers in the automobile are still traveling at the vehicle’s original velocity.

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?

Mass Velocity Time

Momentum Impulse

The impulse experienced by the car equals a change in momentum.

As car designers, we only have control over mass and time.

Influences:

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 anair bagor seatbelt is used to

stop the passenger

No airbag

No seatbelt

No seatbelt with baby

Hit fromHit frombehindbehind

Seat beltsSeat 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

“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.

How many times have you heard people say…

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