Forces and Motion Investigation
A Bad Day for Sandy
UNIT 1 · SECTION 1
Investigate
Experiment
Solve a crash story
Test science ideas
Analyze
Use physics data
LEARNING TARGET
What Will I Learn?
I am learning&
How forces affect motion and accidents.
I will&
Investigate a real-world crash using science.
Work with a partner. You are a science detective!
OUR PLAN
What Are We Doing?
Investigate
Analyze
Use Physics
an accident story
Look at evidence to solve problems
Apply science ideas
Experiment
Simulate
Run experiments
use simulations
VOCABULARY · SECTION 2
Word: Force
Definition
A push or a pull.
Spanish
fuerza
Example
I push the car. That is a force.
VOCABULARY · SECTION 2
Word: Motion
Definition
When something moves from one place to another.
Spanish
movimiento
Example
The car is in motion. It is moving.
VOCABULARY · SECTION 2
Word: Speed
Definition
How fast something moves.
Spanish
velocidad (rapidez)
Example
Sandy drives at 25 mph. That is
her speed.
VOCABULARY · SECTION 2
Word: Friction
Definition
A force that slows things down. It happens when two surfaces
touch.
Spanish
fricción
Example
The brakes create friction. The car slows down.
VOCABULARY · SECTION 2
Word: Acceleration
Definition
A change in speed. Speeding up OR slowing down.
Spanish
aceleración
Example
The car speeds up from 0 to 25 mph. That is acceleration.
VOCABULARY · SECTION 2
Word: Energy
Definition
The ability to do work or cause
motion.
Spanish
energía
Example
A moving car has energy. It can cause damage in a crash.
VOCABULARY · SECTION 2
Word: Engineer
Definition
A person who uses science and math to solve problems.
Spanish
ingeniero / ingeniera
Example
An engineer designs safer cars
and roads.
CASE STUDY
A Bad Day for Sandy
What does the title tell you?What predictions (guess) can you
make?Why would Sandy be having a
Bad Day?
CASE STUDY
The Crash Story
It was a busy Tuesday morning, around 8:00 AM. Sandy was driving her red sedan, heading north towards the intersection of Oak Street and Elm Avenue. The traffic light for her direction was green, and she proceeded cautiously into the intersection.Suddenly, a white pickup truck, traveling east on Elm Avenue, ran its red light. The truck collided with Sandy's car, striking her passenger side with considerable force. The impact spun both vehicles, leaving them disabled in the middle of the intersection.
You will work with partners. Each day they solve one part of the case.
DAILY FOCUS
Essential Question
As we investigate Sandy's crash, today we will explore a core physics
concept:
How do forces affect moving cars?
Consider what pushes, pulls, slows, or stops a vehicle.
Exit Ticket
Complete a KWL about part 1.
Based on what we've learned so far, describe at least one force that would act on Sandy's car just before or during the collision or
complete a KWL chart.
Part 1
The Story&
Questions
Sandy was on her way to the University on a beautiful mild day in March. She was listening to her favorite CD while she thought about the spring break trip she was planning with two of her friends. Just as she approached the corner of South College and Delaware Avenues, she
1.
What questions do the police officers need to answer in order to reconstruct the accident and decide if one of the drivers should be cited?What information will the officers already know, what measurements will they need to make, and what data
2.
noticedthat the light had turned yellow and students were already starting to move across the intersection. She slammed on her brakes and came to a screeching halt. A large delivery truck was following closely behind Sandy's car. Sandy heard brakes screeching behind her and then felt the truck crash into the rear of her car. The impact shoved her car into the intersection before it came to a stop. Luckily, Sandy escaped serious injury, as did the driver of the truck. Unfortunately, her car looked like it
will they need to gather?If Sandy had been traveling at a constant speed of 30 mph, how could you represent her motion as she
3.
drove on S. College Ave.?If she is traveling at a constant speed, what can you say about the forces on the car? 5. What factors influence how quickly a driver can come to a stop?Which factors are influenced by the driver and which
4.
5.
are not?
would be totaled.Two Newark policemen arrived on the scene to investigate the accident. Once they decided that there were no serious injuries, they started investigating the
crash.
DAILY FOCUS
Essential Question Part 2
As we investigate Sandy's crash, today we will explore a core physics
concept:
How do forces affect the body in a crash?
Why did Sandy feel pain?Why did doctors check her heart and bones?
Exit Ticket
What force pulls objects down?
Part 2
Sandy got out of her car and started shaking. She couldn't believe she was okay; the car certainly wasn't. The driver of the delivery truck came over to her and said, "Lady are you crazy4why'd you slam on your brakes? The light was just turning yellow! This accident is your fault!" He then ran over to the policeman and repeated his statements4in fact he repeated his statements several times to the gathering crowd. Sandy was still shaking when the Newark policeman came over and said, "I'm Officer Matthews, are you feeling alright or would you like to be taken to the emergency room?" Sandy told him that her chest hurt from the shoulder strap of her seatbelt, and her neck hurt, but other than that she felt okay. Her car was a "vintage" 1978 Ford, with fixed seatbelts and no airbags. Officer Matthew suggested that she be checked at the emergency room and called for an emergency vehicle to take her there. He reassured her that he would come to the hospital to get more information from her.One hour later, Sandy was still waiting for some x-rays and an EKG when Officer Matthews walked in. She was still giving him information when the nurse came to get her for the medical tests. Officer Matthews returned to the police station to finish the sketch of the accident and record some of the measurements and data he had gathered while investigating the accident.What are some reasons that Officer Matthews suggested that Sandy go to the emergency room?
1.2.3.4.
Why was she having x-rays and EKG? Describe what happens to a person's body in a rear-end collision in terms of forces on the car and body.What are the safety advantages of flexible seatbelts and airbags?
DAILY FOCUS
Essential Question Part 3
As we investigate Sandy's crash, today we will explore a core physics
concept:
How can we use evidence to understand
motion?
What facts do we know?What information is missing?
Exit Ticket
What is speed?
Part 3
Officer Matthews was back at the station, and was preparing to file his report on the accident at the corner of S. College and Delaware Ave. He read through the various statements of the drivers, and witnesses to the
accident.
This is part of the statement made by Sandy Dayton, the owner of the 1978
Ford:
I was heading to class in my car when the light at the intersection turned yellow. I saw students starting to cross, so I hit my brakes, coming to a stop. I heard more screeching of brakes, then a van crashed into the back of my car, throwing my car
into the intersection. I was traveling at thespeed limit, but the driver of the van must have been speeding. I think my car must be totaled! Did you get the van driver's
insurance information?
This is part of the report submitted by the police accident reconstructionist who examined the vehicles at the scene:
At the scene of the accident, it was apparent that the front of the van had been damaged. The car was badly damaged in the rear. There were skid marks, showing that both vehicles had braked. The speedometer of the van was stuck at 15 mph, leading me to believe that the van was traveling at least 15 mph when it crash into the other vehicle.
Part 3&the story&continues
This is part of the statement made by the driver of the van, Jerry Lane:
I had just delivered some boxes at the Ag school and was on my way to deliver the last of my load at Clayton Hall, coming up South College. This college kid in an old beat-up Ford was in front of me when all of a sudden, she slams on her brakes. So did I, but I still slammed into her. The light had just turned yellow, we both had time to go through the light. This is her
fault!
This is a copy of part of Officer Matthew's report on the accident at S.
College and Delaware Avenue:
At 11:35am, Newark Officer Davidson and I received a call on our car radio, directing us to an accident on the corner of S. College and Delaware Avenue. The accident was reported by an unknown witness via a 911 call. We arrived at 11:40am. There was a large group of people around. The driver of the car was sent to the emergency room after complaining of neck and chest pain. The accident appeared to have resulted from a van colliding into the rear of a stopped car at the intersection. The impact moved the car into the intersection. We set up flares, directed traffic around the wreckage site, and called for a
police accident investigation team to be sent over.
Part 3&&.continues
We interviewed some witnesses, including several students. Several told us that it seemed both cars were speeding and almost ran over some students who started to cross the road as the light turned yellow. Others felt that the car and truck were traveling at normal speeds for the area. We took a full statements from three witnesses. We also took a detailed statement from the driver of the van, who appeared to be unhurt. At 12:30pm, I left Officer Davidson and the Accident Investigators at the scene and went to the emergency room to interview Ms. Dayton.
Questions&Part 3
1.2.
From the various accounts of the police officers, the two drivers, and witnesses, what facts do we know in this case?What information do we need to know in order to determine whether a car can safely (legally) go through an intersection
when the light turns yellow as opposed to stopping? What additional information do you need to obtain from the accident report in order to know if Sandy and/or Jerry were
3.
speeding?
DAILY FOCUS
Essential Question Part 4
As we investigate Sandy's crash, today we will explore a core physics
concept:
How can physics help solve accidents?
Exit Ticket
What is friction?
Part 4
Officer Matthews received a more detailed report from the police accident investigator: The 1978 Ford was 30 feet into the intersection, coming to a stop close to the northeast corner of S. College and Delaware Avenue. The 1988 Chevrolet van was found directly behind the car. Both vehicles showed skid marks from the south side of the intersection to the position where they came to a stop. Our analysis showed that the Ford left an 80-foot skid mark prior to being struck by the van, while the van left a 20-foot skid mark prior to impact. A drag sled was used to determine that the average deceleration on the road was 19 ft/s2. The speed limit on S. College is 25 mph. The van weighs approximately twice the weight of the car, and since the car was stopped just prior to impact, speed of the van prior to impact was approximately 1.5 times the speed of the two vehicles just
after impact.QuestionsSketch the intersection, positions of the car and van, and appropriate skid marks. 2. Using what you know about reaction time and stopping distance, how far from the intersection was Sandy when she first saw the students and yellow light?Explain the sequence of events from the time Sandy first noticed the yellow light to the time when both vehicles came to a
1.
2.
stop in the intersection.Should either driver be charged with speeding? Justify your answer with data.Was Jerry following too closely behind Sandy? Do we have data to help answer that question?Should Sandy or Jerry be charged in the accident? Justify your reasoning
3.4.5.
INVESTIGATION
Evidence at the Scene
Skid Marks
Vehicle Damage
Measurements showed 30 feet of tire marks, indicating
Sandy's car had significant damage to the passenger side.
braking.
Witness Statements
Speed Estimates
Several bystanders reported seeing the truck run a red light.
Initial calculations suggest the truck was traveling at a high
speed.
Graph 1
Time (seconds)
Graph 2
DAILY FOCUS
Essential Question Day 5
As we investigate Sandy's crash, today we will explore a core physics
concept:
How do forces and energy affect motion?
Exit Ticket
How do forces affect motion?What is potential energy?
PHYSICS CONCEPT
Newton's First Law
Newton's First Law of Motion, also known as the Law of Inertia,states that an object at rest will stay at rest, and an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced external force.
Constant Motion
Inertia Persists
External Force Applied
Change in Motion
In Sandy's crash, the white pickup truck was in motion. According to Newton's First Law, it would have continued moving straight and at its speed unless something stopped it. That "something" was the impact with Sandy's car, which exerted a powerful external force, causing both vehicles to stop and change their motion.
PHYSICS CONCEPT
Newton's Second Law
Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Simply put, Force equals Mass times Acceleration (F = ma).
=Fma
F (force) m (mass) a (acceleration)This means that a larger force is needed to move or stop a heavier object, or to change an object's speed more quickly.
In Sandy's crash, the white pickup truck had a large mass. When it collided with her car, its motion changed very quickly (high acceleration), creating a tremendous force. This force caused significant damage to Sandy's
sedan.
Example:If a small car (mass acceleration, a truck (mass acceleration generates of force!
) hits at
1000 kg=5000 NF
. But
5 m/s
) hitting at
5000 kg
10 m/s=50000 NF
PHYSICS CONCEPT
Newton's Third Law
Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on a second object, the second object simultaneously exerts a force equal in magnitude and opposite in
direction on the first object.In Sandy's crash, when the pickup truck struck her sedan, Sandy's car exerted an equal and opposite force back onto the truck. This reciprocal force contributed to the damage on both vehicles and the abrupt change in motion for both cars.
ENGINEERING SOLUTIONS
Safety Features: Airbags
Airbags are critical safety devices designed to protect occupants during a collision. They rapidly inflate upon impact, creating a cushion between the
passenger and the vehicle's interior.From a physics perspective, airbags work by increasing the time of impact. Instead of a very short, hard impact (e.g., 0.1 seconds), the airbag extends this time to approximately 0.3 seconds. According to Newton's Second Law (F=ma), increasing the time over which the change in velocity occurs significantly reduces the deceleration (acceleration in the opposite direction). A lower deceleration results in a much smaller force exerted on
the passenger, minimizing injuries.
CHALLENGE
Your Turn: Design a Safety Feature
Imagine you are an engineer tasked with designing a new safety feature for cars. How would you apply your knowledge of physics to reduce injury
in a crash?
Consider these questions for your design:
What specific force are you trying to reduce or distribute in a crash?How will your feature increase the impact time for the occupants, and
why is this important?What materials would you use, and why are they suitable for absorbing or redirecting energy?How does Newton's Laws of Motion apply to your design?Use this space to sketch your ideas and make notes!
SUMMARY
Key Takeaways
Newton's Three Laws
Objects in motion stay in motion (Inertia), Force equals Mass x Acceleration, and for every action, there's an equal and opposite
reaction.
Crash Application
These laws explain the forces involved in Sandy's collision, the sudden stop of vehicles, and the resulting damage.
Engineering Safety
Engineers apply physics (like increasing impact time with airbags) to design features that minimize harm in crashes.
REFLECTION
Reflection: What Have You Learned?
Take a moment to reflect on what you've learned about physics, engineering, and car safety. Consider the following questions:
How do Newton's Laws explain real-world crashes?How do engineers use physics to save lives?What surprised you most about car safety?Use this space to jot down your thoughts and insights.
PHYSICS CONCEPT
Energy Transfer in Collisions
In a collision, kinetic energy (the energy an object possesses due to its motion) is rapidly converted into other forms like heat, sound, and deformation. The amount of kinetic energy is given by the formula:
KE
mv2
Where the energy that must be absorbed during an impact.
is the mass of the object and is its velocity. This means that a heavier vehicle or a higher speed dramatically increases
When a vehicle's speed doubles, its kinetic energy increases fourfold. Similarly, doubling the mass of a vehicle also doubles its kinetic energy. This is why impacts involving heavy vehicles or high speeds are so destructive.
ANALYSIS
Stopping Distance Calculations
Understanding stopping distance is crucial for accident reconstruction and designing safer roads and vehicles. It's the total distance a vehicle travels from the moment a driver perceives a hazard until the vehicle comes to a complete stop.
v=d2¿g
Where:d = stopping distancev = initial velocity (speed) of the vehicle\mu = coefficient of friction between tires and road surfaceg = acceleration due to gravity (The coefficient of friction (\mu) varies significantly with road conditions, impacting how quickly a vehicle can decelerate.
or
9.8 m/s
32.2 ft/s
Example Calculation: Dry Pavement
Let's calculate the stopping distance for a car traveling at
(approx.
) on dry asphalt, where
20 m/s
45 mph
j0.7¿
01
02
03
Identify Variables
Apply Formula
Calculate Result
(20)2×0.7×9.8
=20 m/s=0.7=9.8 m/sg
==
j29.15 meters95.6 feet
v¿
dd
(approx.
40013.72
Stopping Distances for Various Conditions
Speed
Road Condition
\mu (friction)
Stopping Distance
20 m/s (45 mph)
Dry Asphalt
0.7
29.15 m
20 m/s (45 mph)
Wet Asphalt
0.4
51.02 m
20 m/s (45 mph)
Icy Road
0.1
204.08 m
30 m/s (67 mph)
Dry Asphalt
0.7
65.59 m
PHYSICS CONCEPT
The Physics of Friction
Friction is a fundamental force that opposes motion between two surfaces in contact. In the context of vehicles, the friction between the tires and the road surface is crucial for both acceleration and, more importantly, for braking and stopping safely.Without sufficient friction, tires would simply slide, making it impossible to control the vehicle. The amount of friction available, however, changes dramatically with road conditions, directly impacting a vehicle's stopping distance.
Icy Road
Wet Road
Dry Road
As road conditions worsen from dry to icy, the coefficient of friction decreases substantially. This requires significantly greater distances to bring a vehicle to a halt, highlighting the importance of engineering solutions like anti-lock braking systems (ABS)
and specialized tires to maximize friction and ensure safety.
CASE STUDY
Real-World Impact: Sandy's
Recovery
Thanks to modern car safety features, Sandy is on the road to recovery. Her seatbelt prevented her from being ejected and distributed the impact force across her body. The deploying airbags softened her collision with the dashboard, significantly lowering the risk of severe head
and chest injuries.Statistics show seatbelts reduce fatality risk by 45% and serious injury by 50%. Airbags further decrease driver fatalities in frontal crashes by 29%. These engineering marvels, rooted in physics, saved Sandy from much
worse outcomes.
ANALYSIS
Comparing Safety Features
Modern vehicles integrate various safety features, each designed to mitigate the effects of a collision through distinct physical principles. Understanding these mechanisms is crucial for appreciating their combined protective power.
Feature
Primary Mechanism
Key Benefit
Effectiveness
Airbags
Increase Impact Time & Distribute Force
Cushions occupants, spreading force
High
over larger area
Seatbelts
Distribute Force & Prevent
Restrains occupants, spreading force across strong body parts
Very High
Ejection
Crumple Zones
Increase Impact Time
Deforms to absorb energy, extending deceleration time
High
ABS (Anti-lock Braking System)
Maintain Control
Prevents wheel lock-up during braking,
Medium-High
allowing steering
These systems work synergistically to reduce the risk of serious injury by managing the forces and dynamics at play during a crash, often by increasing impact time or distributing force more effectively.
ENGINEERING SOLUTIONS
Safety Features: Anti-lock Braking System (ABS)
Anti-lock Braking Systems (ABS) are a crucial safety innovation designed to prevent the wheels from locking up during emergency braking. This is achieved by rapidly modulating the brake pressure to each wheel, allowing them to continue rotating
rather than skidding.By preventing wheel lockup, ABS maintains directional control and traction, especially on slippery surfaces. This controlled braking significantly reduces stopping distances and allows the driver to steer around obstacles during hard braking, greatly
enhancing safety.
When a driver applies the brakes suddenly, traditional systems can cause wheels to lock, leading to a loss of steering control and increased stopping distance. ABS uses sensors to detect when a wheel is about to lock, then temporarily releases and reapplies brake pressure in rapid succession. This "pumping" action, many times per second, maximizes friction without
skidding.
INTERACTIVE LEARNING
Exploring Physics with PhET Simulations
PhET Interactive Simulations from the University of Colorado Boulder provide engaging, game-like environments for students to explore scientific concepts. We'll be using two key simulations to deepen our understanding of forces, motion, and energy:PhET: Forces and Motion Basics:Investigate how applied forces and friction impact an object's motion. PhET: Pendulum Lab: Observe the interplay between potential and kinetic energy.
Simulation 1: Forces and Motion Basics
01
02
Launch Simulation
Apply Force
Access the "Forces and Motion Basics" PhET simulation.
Experiment with applying different magnitudes of force to
various objects.
03
04
Observe Friction
Record Findings
Notice how the friction force changes and affects the object's
Document your observations on how force, friction, and motion are interconnected.
acceleration and speed.
HANDS-ON PHYSICS
Experiment 2: Forces of Gravity & Friction
Ramp Test
Building on our previous friction experiment, this activity introduces the role of gravity and mass. You will systematically investigate how ramp height, surface type, and object weight influence an object's motion and stopping distance.
1. Set Up Ramp Height2. Explore Surface
3. Vary Object Weight
4. Observe & Analyze
Materials
Motion
Vary the ramp's height to observe how gravity's influence changes the object's speed and the distance it travels. Higher ramps demonstrate greater initial potential energy converting to kinetic energy.
Incrementally add small weights to your object (e.g., a toy car) to increase its mass. Investigate how the change in mass influences the forces required to overcome friction and its overall motion.
Test the object's motion and stopping distance on diverse surfaces like sandpaper, felt, or smooth plastic. Note how different coefficients of friction directly impact the car's deceleration.
Carefully observe and measure distances and record times for each test. Compare how ramp height, surface, and weight collectively influence the car's acceleration, speed, and final stopping position.This experiment helps visualize the interplay between gravitational force, frictional force, and an object's inertia, offering
practical insights into the principles governing motion.
Forces-and-Motion-Investigation.pdf
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Transcript
Forces and Motion Investigation
A Bad Day for Sandy
UNIT 1 · SECTION 1
Investigate
Experiment
Solve a crash story
Test science ideas
Analyze
Use physics data
LEARNING TARGET
What Will I Learn?
I am learning&
How forces affect motion and accidents.
I will&
Investigate a real-world crash using science.
Work with a partner. You are a science detective!
OUR PLAN
What Are We Doing?
Investigate
Analyze
Use Physics
an accident story
Look at evidence to solve problems
Apply science ideas
Experiment
Simulate
Run experiments
use simulations
VOCABULARY · SECTION 2
Word: Force
Definition
A push or a pull.
Spanish
fuerza
Example
I push the car. That is a force.
VOCABULARY · SECTION 2
Word: Motion
Definition
When something moves from one place to another.
Spanish
movimiento
Example
The car is in motion. It is moving.
VOCABULARY · SECTION 2
Word: Speed
Definition
How fast something moves.
Spanish
velocidad (rapidez)
Example
Sandy drives at 25 mph. That is
her speed.
VOCABULARY · SECTION 2
Word: Friction
Definition
A force that slows things down. It happens when two surfaces
touch.
Spanish
fricción
Example
The brakes create friction. The car slows down.
VOCABULARY · SECTION 2
Word: Acceleration
Definition
A change in speed. Speeding up OR slowing down.
Spanish
aceleración
Example
The car speeds up from 0 to 25 mph. That is acceleration.
VOCABULARY · SECTION 2
Word: Energy
Definition
The ability to do work or cause
motion.
Spanish
energía
Example
A moving car has energy. It can cause damage in a crash.
VOCABULARY · SECTION 2
Word: Engineer
Definition
A person who uses science and math to solve problems.
Spanish
ingeniero / ingeniera
Example
An engineer designs safer cars
and roads.
CASE STUDY
A Bad Day for Sandy
What does the title tell you?What predictions (guess) can you
make?Why would Sandy be having a
Bad Day?
CASE STUDY
The Crash Story
It was a busy Tuesday morning, around 8:00 AM. Sandy was driving her red sedan, heading north towards the intersection of Oak Street and Elm Avenue. The traffic light for her direction was green, and she proceeded cautiously into the intersection.Suddenly, a white pickup truck, traveling east on Elm Avenue, ran its red light. The truck collided with Sandy's car, striking her passenger side with considerable force. The impact spun both vehicles, leaving them disabled in the middle of the intersection.
You will work with partners. Each day they solve one part of the case.
DAILY FOCUS
Essential Question
As we investigate Sandy's crash, today we will explore a core physics
concept:
How do forces affect moving cars?
Consider what pushes, pulls, slows, or stops a vehicle.
Exit Ticket
Complete a KWL about part 1.
Based on what we've learned so far, describe at least one force that would act on Sandy's car just before or during the collision or
complete a KWL chart.
Part 1
The Story&
Questions
Sandy was on her way to the University on a beautiful mild day in March. She was listening to her favorite CD while she thought about the spring break trip she was planning with two of her friends. Just as she approached the corner of South College and Delaware Avenues, she
1.
What questions do the police officers need to answer in order to reconstruct the accident and decide if one of the drivers should be cited?What information will the officers already know, what measurements will they need to make, and what data
2.
noticedthat the light had turned yellow and students were already starting to move across the intersection. She slammed on her brakes and came to a screeching halt. A large delivery truck was following closely behind Sandy's car. Sandy heard brakes screeching behind her and then felt the truck crash into the rear of her car. The impact shoved her car into the intersection before it came to a stop. Luckily, Sandy escaped serious injury, as did the driver of the truck. Unfortunately, her car looked like it
will they need to gather?If Sandy had been traveling at a constant speed of 30 mph, how could you represent her motion as she
3.
drove on S. College Ave.?If she is traveling at a constant speed, what can you say about the forces on the car? 5. What factors influence how quickly a driver can come to a stop?Which factors are influenced by the driver and which
4.
5.
are not?
would be totaled.Two Newark policemen arrived on the scene to investigate the accident. Once they decided that there were no serious injuries, they started investigating the
crash.
DAILY FOCUS
Essential Question Part 2
As we investigate Sandy's crash, today we will explore a core physics
concept:
How do forces affect the body in a crash?
Why did Sandy feel pain?Why did doctors check her heart and bones?
Exit Ticket
What force pulls objects down?
Part 2
Sandy got out of her car and started shaking. She couldn't believe she was okay; the car certainly wasn't. The driver of the delivery truck came over to her and said, "Lady are you crazy4why'd you slam on your brakes? The light was just turning yellow! This accident is your fault!" He then ran over to the policeman and repeated his statements4in fact he repeated his statements several times to the gathering crowd. Sandy was still shaking when the Newark policeman came over and said, "I'm Officer Matthews, are you feeling alright or would you like to be taken to the emergency room?" Sandy told him that her chest hurt from the shoulder strap of her seatbelt, and her neck hurt, but other than that she felt okay. Her car was a "vintage" 1978 Ford, with fixed seatbelts and no airbags. Officer Matthew suggested that she be checked at the emergency room and called for an emergency vehicle to take her there. He reassured her that he would come to the hospital to get more information from her.One hour later, Sandy was still waiting for some x-rays and an EKG when Officer Matthews walked in. She was still giving him information when the nurse came to get her for the medical tests. Officer Matthews returned to the police station to finish the sketch of the accident and record some of the measurements and data he had gathered while investigating the accident.What are some reasons that Officer Matthews suggested that Sandy go to the emergency room?
1.2.3.4.
Why was she having x-rays and EKG? Describe what happens to a person's body in a rear-end collision in terms of forces on the car and body.What are the safety advantages of flexible seatbelts and airbags?
DAILY FOCUS
Essential Question Part 3
As we investigate Sandy's crash, today we will explore a core physics
concept:
How can we use evidence to understand
motion?
What facts do we know?What information is missing?
Exit Ticket
What is speed?
Part 3
Officer Matthews was back at the station, and was preparing to file his report on the accident at the corner of S. College and Delaware Ave. He read through the various statements of the drivers, and witnesses to the
accident.
This is part of the statement made by Sandy Dayton, the owner of the 1978
Ford:
I was heading to class in my car when the light at the intersection turned yellow. I saw students starting to cross, so I hit my brakes, coming to a stop. I heard more screeching of brakes, then a van crashed into the back of my car, throwing my car
into the intersection. I was traveling at thespeed limit, but the driver of the van must have been speeding. I think my car must be totaled! Did you get the van driver's
insurance information?
This is part of the report submitted by the police accident reconstructionist who examined the vehicles at the scene:
At the scene of the accident, it was apparent that the front of the van had been damaged. The car was badly damaged in the rear. There were skid marks, showing that both vehicles had braked. The speedometer of the van was stuck at 15 mph, leading me to believe that the van was traveling at least 15 mph when it crash into the other vehicle.
Part 3&the story&continues
This is part of the statement made by the driver of the van, Jerry Lane:
I had just delivered some boxes at the Ag school and was on my way to deliver the last of my load at Clayton Hall, coming up South College. This college kid in an old beat-up Ford was in front of me when all of a sudden, she slams on her brakes. So did I, but I still slammed into her. The light had just turned yellow, we both had time to go through the light. This is her
fault!
This is a copy of part of Officer Matthew's report on the accident at S.
College and Delaware Avenue:
At 11:35am, Newark Officer Davidson and I received a call on our car radio, directing us to an accident on the corner of S. College and Delaware Avenue. The accident was reported by an unknown witness via a 911 call. We arrived at 11:40am. There was a large group of people around. The driver of the car was sent to the emergency room after complaining of neck and chest pain. The accident appeared to have resulted from a van colliding into the rear of a stopped car at the intersection. The impact moved the car into the intersection. We set up flares, directed traffic around the wreckage site, and called for a
police accident investigation team to be sent over.
Part 3&&.continues
We interviewed some witnesses, including several students. Several told us that it seemed both cars were speeding and almost ran over some students who started to cross the road as the light turned yellow. Others felt that the car and truck were traveling at normal speeds for the area. We took a full statements from three witnesses. We also took a detailed statement from the driver of the van, who appeared to be unhurt. At 12:30pm, I left Officer Davidson and the Accident Investigators at the scene and went to the emergency room to interview Ms. Dayton.
Questions&Part 3
1.2.
From the various accounts of the police officers, the two drivers, and witnesses, what facts do we know in this case?What information do we need to know in order to determine whether a car can safely (legally) go through an intersection
when the light turns yellow as opposed to stopping? What additional information do you need to obtain from the accident report in order to know if Sandy and/or Jerry were
3.
speeding?
DAILY FOCUS
Essential Question Part 4
As we investigate Sandy's crash, today we will explore a core physics
concept:
How can physics help solve accidents?
Exit Ticket
What is friction?
Part 4
Officer Matthews received a more detailed report from the police accident investigator: The 1978 Ford was 30 feet into the intersection, coming to a stop close to the northeast corner of S. College and Delaware Avenue. The 1988 Chevrolet van was found directly behind the car. Both vehicles showed skid marks from the south side of the intersection to the position where they came to a stop. Our analysis showed that the Ford left an 80-foot skid mark prior to being struck by the van, while the van left a 20-foot skid mark prior to impact. A drag sled was used to determine that the average deceleration on the road was 19 ft/s2. The speed limit on S. College is 25 mph. The van weighs approximately twice the weight of the car, and since the car was stopped just prior to impact, speed of the van prior to impact was approximately 1.5 times the speed of the two vehicles just
after impact.QuestionsSketch the intersection, positions of the car and van, and appropriate skid marks. 2. Using what you know about reaction time and stopping distance, how far from the intersection was Sandy when she first saw the students and yellow light?Explain the sequence of events from the time Sandy first noticed the yellow light to the time when both vehicles came to a
1.
2.
stop in the intersection.Should either driver be charged with speeding? Justify your answer with data.Was Jerry following too closely behind Sandy? Do we have data to help answer that question?Should Sandy or Jerry be charged in the accident? Justify your reasoning
3.4.5.
INVESTIGATION
Evidence at the Scene
Skid Marks
Vehicle Damage
Measurements showed 30 feet of tire marks, indicating
Sandy's car had significant damage to the passenger side.
braking.
Witness Statements
Speed Estimates
Several bystanders reported seeing the truck run a red light.
Initial calculations suggest the truck was traveling at a high
speed.
Graph 1
Time (seconds)
Graph 2
DAILY FOCUS
Essential Question Day 5
As we investigate Sandy's crash, today we will explore a core physics
concept:
How do forces and energy affect motion?
Exit Ticket
How do forces affect motion?What is potential energy?
PHYSICS CONCEPT
Newton's First Law
Newton's First Law of Motion, also known as the Law of Inertia,states that an object at rest will stay at rest, and an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced external force.
Constant Motion
Inertia Persists
External Force Applied
Change in Motion
In Sandy's crash, the white pickup truck was in motion. According to Newton's First Law, it would have continued moving straight and at its speed unless something stopped it. That "something" was the impact with Sandy's car, which exerted a powerful external force, causing both vehicles to stop and change their motion.
PHYSICS CONCEPT
Newton's Second Law
Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Simply put, Force equals Mass times Acceleration (F = ma).
=Fma
F (force) m (mass) a (acceleration)This means that a larger force is needed to move or stop a heavier object, or to change an object's speed more quickly.
In Sandy's crash, the white pickup truck had a large mass. When it collided with her car, its motion changed very quickly (high acceleration), creating a tremendous force. This force caused significant damage to Sandy's
sedan.
Example:If a small car (mass acceleration, a truck (mass acceleration generates of force!
) hits at
1000 kg=5000 NF
. But
5 m/s
) hitting at
5000 kg
10 m/s=50000 NF
PHYSICS CONCEPT
Newton's Third Law
Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on a second object, the second object simultaneously exerts a force equal in magnitude and opposite in
direction on the first object.In Sandy's crash, when the pickup truck struck her sedan, Sandy's car exerted an equal and opposite force back onto the truck. This reciprocal force contributed to the damage on both vehicles and the abrupt change in motion for both cars.
ENGINEERING SOLUTIONS
Safety Features: Airbags
Airbags are critical safety devices designed to protect occupants during a collision. They rapidly inflate upon impact, creating a cushion between the
passenger and the vehicle's interior.From a physics perspective, airbags work by increasing the time of impact. Instead of a very short, hard impact (e.g., 0.1 seconds), the airbag extends this time to approximately 0.3 seconds. According to Newton's Second Law (F=ma), increasing the time over which the change in velocity occurs significantly reduces the deceleration (acceleration in the opposite direction). A lower deceleration results in a much smaller force exerted on
the passenger, minimizing injuries.
CHALLENGE
Your Turn: Design a Safety Feature
Imagine you are an engineer tasked with designing a new safety feature for cars. How would you apply your knowledge of physics to reduce injury
in a crash?
Consider these questions for your design:
What specific force are you trying to reduce or distribute in a crash?How will your feature increase the impact time for the occupants, and
why is this important?What materials would you use, and why are they suitable for absorbing or redirecting energy?How does Newton's Laws of Motion apply to your design?Use this space to sketch your ideas and make notes!
SUMMARY
Key Takeaways
Newton's Three Laws
Objects in motion stay in motion (Inertia), Force equals Mass x Acceleration, and for every action, there's an equal and opposite
reaction.
Crash Application
These laws explain the forces involved in Sandy's collision, the sudden stop of vehicles, and the resulting damage.
Engineering Safety
Engineers apply physics (like increasing impact time with airbags) to design features that minimize harm in crashes.
REFLECTION
Reflection: What Have You Learned?
Take a moment to reflect on what you've learned about physics, engineering, and car safety. Consider the following questions:
How do Newton's Laws explain real-world crashes?How do engineers use physics to save lives?What surprised you most about car safety?Use this space to jot down your thoughts and insights.
PHYSICS CONCEPT
Energy Transfer in Collisions
In a collision, kinetic energy (the energy an object possesses due to its motion) is rapidly converted into other forms like heat, sound, and deformation. The amount of kinetic energy is given by the formula:
KE
mv2
Where the energy that must be absorbed during an impact.
is the mass of the object and is its velocity. This means that a heavier vehicle or a higher speed dramatically increases
When a vehicle's speed doubles, its kinetic energy increases fourfold. Similarly, doubling the mass of a vehicle also doubles its kinetic energy. This is why impacts involving heavy vehicles or high speeds are so destructive.
ANALYSIS
Stopping Distance Calculations
Understanding stopping distance is crucial for accident reconstruction and designing safer roads and vehicles. It's the total distance a vehicle travels from the moment a driver perceives a hazard until the vehicle comes to a complete stop.
v=d2¿g
Where:d = stopping distancev = initial velocity (speed) of the vehicle\mu = coefficient of friction between tires and road surfaceg = acceleration due to gravity (The coefficient of friction (\mu) varies significantly with road conditions, impacting how quickly a vehicle can decelerate.
or
9.8 m/s
32.2 ft/s
Example Calculation: Dry Pavement
Let's calculate the stopping distance for a car traveling at
(approx.
) on dry asphalt, where
20 m/s
45 mph
j0.7¿
01
02
03
Identify Variables
Apply Formula
Calculate Result
(20)2×0.7×9.8
=20 m/s=0.7=9.8 m/sg
==
j29.15 meters95.6 feet
v¿
dd
(approx.
40013.72
Stopping Distances for Various Conditions
Speed
Road Condition
\mu (friction)
Stopping Distance
20 m/s (45 mph)
Dry Asphalt
0.7
29.15 m
20 m/s (45 mph)
Wet Asphalt
0.4
51.02 m
20 m/s (45 mph)
Icy Road
0.1
204.08 m
30 m/s (67 mph)
Dry Asphalt
0.7
65.59 m
PHYSICS CONCEPT
The Physics of Friction
Friction is a fundamental force that opposes motion between two surfaces in contact. In the context of vehicles, the friction between the tires and the road surface is crucial for both acceleration and, more importantly, for braking and stopping safely.Without sufficient friction, tires would simply slide, making it impossible to control the vehicle. The amount of friction available, however, changes dramatically with road conditions, directly impacting a vehicle's stopping distance.
Icy Road
Wet Road
Dry Road
As road conditions worsen from dry to icy, the coefficient of friction decreases substantially. This requires significantly greater distances to bring a vehicle to a halt, highlighting the importance of engineering solutions like anti-lock braking systems (ABS)
and specialized tires to maximize friction and ensure safety.
CASE STUDY
Real-World Impact: Sandy's
Recovery
Thanks to modern car safety features, Sandy is on the road to recovery. Her seatbelt prevented her from being ejected and distributed the impact force across her body. The deploying airbags softened her collision with the dashboard, significantly lowering the risk of severe head
and chest injuries.Statistics show seatbelts reduce fatality risk by 45% and serious injury by 50%. Airbags further decrease driver fatalities in frontal crashes by 29%. These engineering marvels, rooted in physics, saved Sandy from much
worse outcomes.
ANALYSIS
Comparing Safety Features
Modern vehicles integrate various safety features, each designed to mitigate the effects of a collision through distinct physical principles. Understanding these mechanisms is crucial for appreciating their combined protective power.
Feature
Primary Mechanism
Key Benefit
Effectiveness
Airbags
Increase Impact Time & Distribute Force
Cushions occupants, spreading force
High
over larger area
Seatbelts
Distribute Force & Prevent
Restrains occupants, spreading force across strong body parts
Very High
Ejection
Crumple Zones
Increase Impact Time
Deforms to absorb energy, extending deceleration time
High
ABS (Anti-lock Braking System)
Maintain Control
Prevents wheel lock-up during braking,
Medium-High
allowing steering
These systems work synergistically to reduce the risk of serious injury by managing the forces and dynamics at play during a crash, often by increasing impact time or distributing force more effectively.
ENGINEERING SOLUTIONS
Safety Features: Anti-lock Braking System (ABS)
Anti-lock Braking Systems (ABS) are a crucial safety innovation designed to prevent the wheels from locking up during emergency braking. This is achieved by rapidly modulating the brake pressure to each wheel, allowing them to continue rotating
rather than skidding.By preventing wheel lockup, ABS maintains directional control and traction, especially on slippery surfaces. This controlled braking significantly reduces stopping distances and allows the driver to steer around obstacles during hard braking, greatly
enhancing safety.
When a driver applies the brakes suddenly, traditional systems can cause wheels to lock, leading to a loss of steering control and increased stopping distance. ABS uses sensors to detect when a wheel is about to lock, then temporarily releases and reapplies brake pressure in rapid succession. This "pumping" action, many times per second, maximizes friction without
skidding.
INTERACTIVE LEARNING
Exploring Physics with PhET Simulations
PhET Interactive Simulations from the University of Colorado Boulder provide engaging, game-like environments for students to explore scientific concepts. We'll be using two key simulations to deepen our understanding of forces, motion, and energy:PhET: Forces and Motion Basics:Investigate how applied forces and friction impact an object's motion. PhET: Pendulum Lab: Observe the interplay between potential and kinetic energy.
Simulation 1: Forces and Motion Basics
01
02
Launch Simulation
Apply Force
Access the "Forces and Motion Basics" PhET simulation.
Experiment with applying different magnitudes of force to
various objects.
03
04
Observe Friction
Record Findings
Notice how the friction force changes and affects the object's
Document your observations on how force, friction, and motion are interconnected.
acceleration and speed.
HANDS-ON PHYSICS
Experiment 2: Forces of Gravity & Friction
Ramp Test
Building on our previous friction experiment, this activity introduces the role of gravity and mass. You will systematically investigate how ramp height, surface type, and object weight influence an object's motion and stopping distance.
1. Set Up Ramp Height2. Explore Surface
3. Vary Object Weight
4. Observe & Analyze
Materials
Motion
Vary the ramp's height to observe how gravity's influence changes the object's speed and the distance it travels. Higher ramps demonstrate greater initial potential energy converting to kinetic energy.
Incrementally add small weights to your object (e.g., a toy car) to increase its mass. Investigate how the change in mass influences the forces required to overcome friction and its overall motion.
Test the object's motion and stopping distance on diverse surfaces like sandpaper, felt, or smooth plastic. Note how different coefficients of friction directly impact the car's deceleration.
Carefully observe and measure distances and record times for each test. Compare how ramp height, surface, and weight collectively influence the car's acceleration, speed, and final stopping position.This experiment helps visualize the interplay between gravitational force, frictional force, and an object's inertia, offering
practical insights into the principles governing motion.