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Demos Demos Ball Ball Tennis ball on string Tennis ball on string Two same size cookie boxes Two same size cookie boxes Styrofoam, piece of plywood, Styrofoam, piece of plywood, hammer hammer Master Cylinder Brake Master Cylinder Brake Box with sandpaper on bottom Box with sandpaper on bottom (datastudio) (datastudio) Feather and penny in tube Feather and penny in tube

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Page 1: Demos Ball Ball Tennis ball on string Tennis ball on string Two same size cookie boxes Two same size cookie boxes Styrofoam, piece of plywood, hammer Styrofoam,

DemosDemos BallBall Tennis ball on stringTennis ball on string Two same size cookie boxesTwo same size cookie boxes Styrofoam, piece of plywood, Styrofoam, piece of plywood,

hammerhammer Master Cylinder BrakeMaster Cylinder Brake Box with sandpaper on bottom Box with sandpaper on bottom

(datastudio)(datastudio) Feather and penny in tubeFeather and penny in tube

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Managing Managing AccelerationAcceleration

Wikipedia

http://www.gregscoasterphotos.com

http://www.local6.com/news

www.dowwallpaper.com

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What is acceleration?What is acceleration? Why we need to manage acceleration Why we need to manage acceleration

in cars and other high speed in cars and other high speed conveyances.conveyances. Crash Tests with and without restraint Crash Tests with and without restraint

systemssystems How to minimize dangerous How to minimize dangerous

accelerations.accelerations. Air bagsAir bags SeatbeltsSeatbelts Anti-lock and Hydraulic brakes (avoiding Anti-lock and Hydraulic brakes (avoiding

accidents)accidents) Softer/deformable interior materials.Softer/deformable interior materials. The Crumple ZoneThe Crumple Zone

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What is velocity?What is velocity?

MotionMotion speed and directionspeed and direction 40 mph due West40 mph due West is an example of is an example of

velocityvelocity 40 mph40 mph is speed (because no is speed (because no

direction is given)direction is given)

When any part of velocity changes (speed and/or direction), we say there is acceleration.

Acceleration is change in velocity!

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Velocity = distance/timeVelocity = distance/time(in a certain direction)(in a certain direction)

examples of velocity units:examples of velocity units: Meters/secondMeters/second Miles per hourMiles per hour Feet per secondFeet per second Kilometers per hourKilometers per hour

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AccelerationAcceleration

Change in speedChange in speedChange in directionChange in direction

Slowing down is negative accelerationSlowing down is negative acceleration

Making a sharp right turn is accelerationMaking a sharp right turn is acceleration

Flooring the accelerator is positive Flooring the accelerator is positive accelerationacceleration

Driving over a speed bump is Driving over a speed bump is accelerationacceleration

Riding on a Merry-go-RoundRiding on a Merry-go-Round

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Examples of zero Examples of zero accelerationacceleration

No change in motionNo change in motion A plane flying steadily and in a straight line A plane flying steadily and in a straight line

at 700 mphat 700 mph An elevator that is moving at a steady paceAn elevator that is moving at a steady pace Your house when there isn’t an earthquakeYour house when there isn’t an earthquake

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Equations for finding Equations for finding accelerationacceleration

a = (Va = (Vff – V – Vii)/ t)/ t

a = -½ Va = -½ Vii22 / d (V / d (Vf f = 0)= 0)

a – average accelerationa – average acceleration

VVii – initial speed/velocity – initial speed/velocity

VVff – final speed – final speed

t – timet – time

d – distance taken to stopd – distance taken to stop

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Aristotle (384 BC – 322 BC), Aristotle (384 BC – 322 BC), the great Greek philosopher the great Greek philosopher

believed….believed….

It is natural for things to be at rest. It is natural for things to be at rest. Objects at rest require no explanation.Objects at rest require no explanation.

Objects in motion require an Objects in motion require an explanation.explanation.

Aristotle believed a force is required Aristotle believed a force is required to keep an object in motion.to keep an object in motion.

What do you think?What do you think?

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Galileo Galilei (1564-1642)Galileo Galilei (1564-1642)

Questioned this Questioned this 1900 year-old 1900 year-old AristotelianAristotelian view view

Thought that Thought that maybe objects in maybe objects in constant motion constant motion may not need a may not need a force to remain in force to remain in motion.motion.

http://www.practicalphysics.org

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Galileo showed…Galileo showed…

Motion in a straight line at constant Motion in a straight line at constant speed does not require a force.speed does not require a force.

Objects at rest or in motion (moving Objects at rest or in motion (moving in a straight line at a constant speed) in a straight line at a constant speed) are natural states.are natural states.

Forces cause a Forces cause a changechange in motion in motion Aristotle was incorrect to believed Aristotle was incorrect to believed

that forces cause motion.that forces cause motion.

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A change in motion is a change in A change in motion is a change in direction and/or speed.direction and/or speed.

Acceleration is the rate of change of Acceleration is the rate of change of motion.motion.

Acceleration depends on the force applied Acceleration depends on the force applied and the mass of the object.and the mass of the object.

F F acceleration acceleration

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Galileo’s other studies of Galileo’s other studies of motionmotion

Galileo showed that all objects fall at Galileo showed that all objects fall at the same rate at the earth’s surface.the same rate at the earth’s surface.

Galileo used an Galileo used an inclined planeinclined plane to to lessen the earth’s pull on objects.lessen the earth’s pull on objects.

This allowed Galileo to do his This allowed Galileo to do his experiments without extremely experiments without extremely accurate time pieces.accurate time pieces.

Prior to Galileo’s experiments with Prior to Galileo’s experiments with falling objects, most scientists falling objects, most scientists believed that heavier objects fell believed that heavier objects fell faster than lighter objects.faster than lighter objects.

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Galileo’s ApparatusGalileo’s Apparatus

Galileo found that Galileo found that objects fall at 9.8 objects fall at 9.8 m/sm/s22

Every second the Every second the velocity of a falling velocity of a falling object increases by object increases by 9.8 m/s 9.8 m/s

Experiment Experiment reduced the effects reduced the effects of friction and air of friction and air resitance.resitance. http://ircamera.as.arizona.edu

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Gravitational AccelerationGravitational Acceleration All objects fall to the earth with the All objects fall to the earth with the

same acceleration. (ex. Feather and same acceleration. (ex. Feather and penny in tube)penny in tube)

This acceleration = 9.8 m/sThis acceleration = 9.8 m/s22

A falling object will increase its speed by 9.8 A falling object will increase its speed by 9.8 m/s every second it falls. (m/s every second it falls. (assuming no air assuming no air resistanceresistance))

1 g = 9.8 m/s1 g = 9.8 m/s22

You are experiencing 1 g “pull” towards earth You are experiencing 1 g “pull” towards earth as you sit in the classroomas you sit in the classroom

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Isaac Newton (1642-1727)Isaac Newton (1642-1727)

Continued Galileo’s Continued Galileo’s study of motionstudy of motion

Studied motion while Studied motion while alone on his farm during alone on his farm during the plague while the plague while Cambridge was closed.Cambridge was closed.

http://content.answers.com

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Isaac Newton expressed the laws of motion Isaac Newton expressed the laws of motion as as

3 laws and explained why they are 3 laws and explained why they are UNIVERSAL laws UNIVERSAL laws

(they apply everywhere, not just on earth)(they apply everywhere, not just on earth)

Newton’s First Law of Motion states:Newton’s First Law of Motion states: Objects at rest tend to stay at rest unless Objects at rest tend to stay at rest unless

a net force is applied to them.a net force is applied to them.

Objects in motion tend to stay in motion Objects in motion tend to stay in motion and continue in a straight line unless a and continue in a straight line unless a force is applied to themforce is applied to them

Rest or Constant speed in a straight line is Rest or Constant speed in a straight line is called called Uniform Motion.Uniform Motion.

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Example of the first lawExample of the first law

Objects lying around don’t “walk away” on Objects lying around don’t “walk away” on their own. (i.e. blame your room-mates)their own. (i.e. blame your room-mates)

Without seatbelts, a person can get ejected Without seatbelts, a person can get ejected from a car that suddenly stops.from a car that suddenly stops.

http://youtube.com/watch?v=giYQE1Hskjc&mode=related&search==

http://youtube.com/watch?v=xU2jrQ4uunU&feature=related

http://www.nhtsa.dot.gov

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Any motion that IS NOT Uniform Motion, is Any motion that IS NOT Uniform Motion, is acceleration and requires a force.acceleration and requires a force.

Prior to Newton, scientists thought that Prior to Newton, scientists thought that celestial bodies (moons, planets) that moved celestial bodies (moons, planets) that moved in circles did not have forces acting on them.in circles did not have forces acting on them.

Heavenly bodies never stopped orbiting so Heavenly bodies never stopped orbiting so people assumed the “steady state” of the people assumed the “steady state” of the heavens implied that no forces acted on heavens implied that no forces acted on orbiting bodies seen in space.orbiting bodies seen in space.

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Newton understands that circular Newton understands that circular motion must require a force…. So motion must require a force…. So what does this mean for the earth’s what does this mean for the earth’s moon?moon?

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Newton and the Newton and the AppleApple

Newton did tend an apple orchardNewton did tend an apple orchard Claims he did have a breakthrough Claims he did have a breakthrough

moment while daydreaming theremoment while daydreaming there Newton saw the apple and moon together Newton saw the apple and moon together

in the skyin the sky Newton makes the connection that the Newton makes the connection that the

moon is like a VERY large apple only moon is like a VERY large apple only farther awayfarther away

An apple thrown fast enough could be put An apple thrown fast enough could be put into orbit just like the moon.into orbit just like the moon.

Realizes that the moon IS falling towards Realizes that the moon IS falling towards the earth due to gravity but that its the earth due to gravity but that its distance from the earth never changes distance from the earth never changes due to the curvature of the earthdue to the curvature of the earth

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Newton’s Laws of Motion are Newton’s Laws of Motion are UniversalUniversal

Newton realizes that laws of Newton realizes that laws of motion that describe motion on motion that describe motion on earth should be universal and earth should be universal and apply to motion of bodies in the apply to motion of bodies in the universe.universe.

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Newton’s 2Newton’s 2ndnd Law of Motion Law of Motion states:states:

Force on an object is the object’sForce on an object is the object’s

Mass times Acceleration.Mass times Acceleration.

F = maF = maF – Force

m – mass (how much matter or atoms make up the object)

a – acceleration (rate at which speed or direction changes)

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Examples of the 2Examples of the 2ndnd Law Law More massive objects weigh moreMore massive objects weigh more

F = mgF = mg It is harder to throw a bowling ball than a It is harder to throw a bowling ball than a

tennis balltennis ball I’d rather be hit by an acorn than a big I’d rather be hit by an acorn than a big

green pine cone going the same speedgreen pine cone going the same speedF = maF = ma

It takes more force to accelerate a big It takes more force to accelerate a big mass compared to a small mass. This is mass compared to a small mass. This is one reason why heavy and light objects one reason why heavy and light objects in a vacuum fall to earth at the same in a vacuum fall to earth at the same rate.rate.

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If there is a force on you right If there is a force on you right now? Why are you not now? Why are you not

accelerating?accelerating?

A force does not always produce A force does not always produce acceleration, but if all the forces on a acceleration, but if all the forces on a body/object added together do not body/object added together do not equal ZERO, then the net force will equal ZERO, then the net force will produce accelerationproduce acceleration

This leads us to the Newton’s 3This leads us to the Newton’s 3rdrd Law Law

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Newton’s Third Law of Motion states:Newton’s Third Law of Motion states:

For Every force there is an equal but For Every force there is an equal but opposite force.opposite force.

http://www.answers.com

www.primidi.com

www.the-fitness-motivator.com

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Where’s the equal Where’s the equal but opposite force?but opposite force?

The earth is also The earth is also accelerating accelerating towards the towards the skydiver but the skydiver but the acceleration is acceleration is very, very small … very, very small … or cancelled out by or cancelled out by someone skydiving someone skydiving on the other side of on the other side of the earth.the earth.

www.blackfive.net

3rd Law: Forces come in pairs

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Forces always come in pairsForces always come in pairs

Examples:Examples: Sitting on a chairSitting on a chair Squishing a styrofoam ballSquishing a styrofoam ball A car hitting a metal guard railA car hitting a metal guard rail Two cars collidingTwo cars colliding If you want to determine the If you want to determine the

force force of a crash, you can either of a crash, you can either inspect inspect damage to the car or damage to the car or inspect inspect damage to what the car hit.damage to what the car hit.

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All objectsAll objects with mass are attracted to with mass are attracted to each other – this attractive force is each other – this attractive force is

called called gravitygravity

Newton’s Law of Newton’s Law of Universal GravitationUniversal Gravitation Force = G x mForce = G x m11 x m x m22 / d / d22

G is a universal constantG is a universal constant From this equation the earth’s mass From this equation the earth’s mass

can be calculated.can be calculated.

M1M2

d

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Henry Cavendish devises an experiment that allows him to find Big G

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The force between two The force between two 150 lb. people 3’ apart is 150 lb. people 3’ apart is

about the weight of a flea.about the weight of a flea.

Gravity is a VERY weak force but Gravity is a VERY weak force but the earth is so massive that the the earth is so massive that the

force is exerts on us is very force is exerts on us is very noticeable.noticeable.

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What is a potentially What is a potentially dangerous acceleration?dangerous acceleration?

Slamming on the breaksSlamming on the breaks Hitting a brick wallHitting a brick wall If a force of 4 to 6 g is sustained for If a force of 4 to 6 g is sustained for

more than a few seconds, the more than a few seconds, the resulting symptoms range from resulting symptoms range from visual impairment to total blackout. visual impairment to total blackout.

Crash victims sustain greater g Crash victims sustain greater g forces but experience them for forces but experience them for approx. less than 150 msapprox. less than 150 ms

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““The acceleration during the crash The acceleration during the crash that killed Diana, Princess of Wales, in that killed Diana, Princess of Wales, in 1997 was estimated to have been on 1997 was estimated to have been on the order of 70 to 100 g, which was the order of 70 to 100 g, which was intense enough to tear the pulmonary intense enough to tear the pulmonary artery from her heart -- an injury that artery from her heart -- an injury that is nearly impossible to survive. Had is nearly impossible to survive. Had she been wearing a seat belt, the she been wearing a seat belt, the acceleration would have been acceleration would have been something more like 30 or 35 g - something more like 30 or 35 g - enough to break a rib or two, but not enough to break a rib or two, but not nearly enough to kill most people.”nearly enough to kill most people.”

http://hypertextbook.com/physics/http://hypertextbook.com/physics/

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Automotive Accelerations (g)

event typical carsports car

race car

large truck

starting 0.3 - 0.5 > 0.9 1.7 < 0.2

braking 0.8 - 1.0 > 1.3 2 ~ 0.6

cornering 0.6 - 1.0 > 2.5 3 ?? 

http://hypertextbook.com

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Fighter Pilots may Fighter Pilots may experience experience

up to 9gup to 9gA pilot weighing 180 lbs. will feel as if A pilot weighing 180 lbs. will feel as if s/he weighs 180 X 9 or 1620 lbs.s/he weighs 180 X 9 or 1620 lbs.

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Technologies used to minimize Technologies used to minimize dangerous accelerations in dangerous accelerations in

carscars Seatbelts and the webbingSeatbelts and the webbing Air bagsAir bags The Crumple zoneThe Crumple zone Deformable dashboard and steering Deformable dashboard and steering

wheelwheel Hydraulic brakesHydraulic brakes Anti-lock brakesAnti-lock brakes

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Seatbelts do three things:Seatbelts do three things:

Apply forces to the parts of the body that Apply forces to the parts of the body that are tough (rib cage and pelvis)are tough (rib cage and pelvis)

Prevent the human from impacting rigid Prevent the human from impacting rigid objects.objects.

Reduce the acceleration on the body by Reduce the acceleration on the body by restraining the body continuously restraining the body continuously throughout the crash.throughout the crash.

Energy = F x distanceEnergy = F x distance

By increasing the stopping distance of the By increasing the stopping distance of the human the forces are lowered.human the forces are lowered.

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Inertia triggered retractorsInertia triggered retractors(Inertia is determined by mass and it is the (Inertia is determined by mass and it is the

resistance to changes in motion)resistance to changes in motion)

Pawl Ratchet Gear

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Belt Triggered Retractor – page Belt Triggered Retractor – page 7575

Seatbelts typically lock up around ½ g

Clutch

Toothed Plate

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Clutch – a mechanism for transmitting Clutch – a mechanism for transmitting rotation, which can be engaged or rotation, which can be engaged or disengaged disengaged (Wikipedia) (Wikipedia)

Ratchet – a device that (when engaged) Ratchet – a device that (when engaged) allows for linear or rotational motion in allows for linear or rotational motion in one direction onlyone direction only

Pawl – a piece with a pointed end that Pawl – a piece with a pointed end that engages with the ratchet and locks itengages with the ratchet and locks it

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Determine type of seatbeltDetermine type of seatbeltgiven in classgiven in class

Triggered by yanking on the belt or Triggered by yanking on the belt or by changes to acceleration?by changes to acceleration?

Locate the pawl, ratchet, toothed Locate the pawl, ratchet, toothed plate, and any other important plate, and any other important component.component.

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In the event of a crash, a pretensioner will tighten In the event of a crash, a pretensioner will tighten the belt almost instantaneously. Like the belt almost instantaneously. Like airbags, , pretensioners are triggered by sensors in the pretensioners are triggered by sensors in the car's body, and most pretensioners use car's body, and most pretensioners use explosively expanding gas to drive a piston that explosively expanding gas to drive a piston that retracts the belt. retracts the belt. WikipediaWikipedia

Gas is ignited here

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www.abetterwindshield.com

Airbags Airbags inflate and inflate and apply forces apply forces evenlyevenly to the to the windshield, windshield, dash, and dash, and occupant occupant over a time over a time period of period of about 100 msabout 100 ms

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What makes an airbag What makes an airbag inflate?inflate?

The accelerometer is builtinto a microchip. DuringLarge decelerations, the massof the accelerometer shifts.This closes an electrical contacttriggering the bag to inflate.

Sodium Azide (NaN3) reacts with Potassium Nitrate (KNO3) to produce nitrogen gas The bag inflates in 40 msThe bag has tiny holes in it allowing the gas to escape so that the bag absorbs energy.

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Is an air bag dangerous?Is an air bag dangerous?

Inflating in 40 ms implies that the bag Inflating in 40 ms implies that the bag is actually exploding.is actually exploding.

Occupants should be >10 inches away Occupants should be >10 inches away from the steering wheelfrom the steering wheel

If the occupant hits the air bag before If the occupant hits the air bag before it is fully inflated injury can occur. it is fully inflated injury can occur. When the bag inflates it does so at When the bag inflates it does so at approx. 100 mph.approx. 100 mph.

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How effective are air bags?How effective are air bags?

Seatbelts are 42% effective at Seatbelts are 42% effective at preventing driver fatalities.preventing driver fatalities.

Seatbelts with air bags are 49% Seatbelts with air bags are 49% effective at preventing driver effective at preventing driver fatalities.fatalities.

Airbags reduce the risk of death by only Airbags reduce the risk of death by only 7%7%

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246 people died from air bags from 246 people died from air bags from 1986-2001 (75% were women)1986-2001 (75% were women)

7,000 people were saved from air bags 7,000 people were saved from air bags during the same 15 year periodduring the same 15 year period

11,000 people are saved 11,000 people are saved annuallyannually due due to seat beltsto seat belts

People less than 5’3” tall are more People less than 5’3” tall are more harmed with an air bag than without it harmed with an air bag than without it during a crash because shorter drivers during a crash because shorter drivers sit close to the steering wheel.sit close to the steering wheel.

http://www.youtube.com/watch?v=-lHI5BwFl_w&NR=1

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Mercury Sensorhttp://www.autoshop101.com

SensorsSensors

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The role of deformable The role of deformable materialsmaterials

Reduce accelerations on a human’s Reduce accelerations on a human’s bodybody

Increase the stopping time and distanceIncrease the stopping time and distance E = Force * distance (increase distance E = Force * distance (increase distance

so that the energy is absorbed at a so that the energy is absorbed at a lower force)lower force)

Less bouncing – multiple hard hits are Less bouncing – multiple hard hits are more damaging that one force applied more damaging that one force applied more continuouslymore continuously

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Crumple Zone absorbs Crumple Zone absorbs energyenergy

KE = ½ mvKE = ½ mv22

Kinetic Energy needs to be absorbed Kinetic Energy needs to be absorbed quickly in an area outside of the quickly in an area outside of the driving compartmentdriving compartment

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Crumple ZoneCrumple Zone

http://www.aip.org/dbis/stories/2004/14124.html

Page 54: Demos Ball Ball Tennis ball on string Tennis ball on string Two same size cookie boxes Two same size cookie boxes Styrofoam, piece of plywood, hammer Styrofoam,

SourcesSources

http://auto.howstuffworks.com/seatbelt.htm

http://auto.howstuffworks.com/airbag.htm