Good Morning! Today we will:
complete Investigation 3.3
watch a video
Please do before the tardy bell:
get out your lab notebook & something to write with
have at least one textbook on your desk
be sitting at a table with at least one other person but no more than two other people

Energy & Work :

Energy & Work Why Air Bags?

What Do You See? :

What Do You See?

Investigation 3.3 :

Investigation 3.3 Turn to the first new page in your lab book and title this lab, “Why Air Bags?” Be sure to make an entry in your Table of Contents as well.

Air Bags :

Air Bags How does an air bag protect you during an accident?
Copy this question down in your lab notebook and take 5 minutes to jot down your ideas.

Air Bags :

Air Bags How does an air bag protect you during an accident?
Now take three minutes and share your ideas with your table partner
If you sit on an odd number row, turn around and share your ideas with the table behind you.

Investigation 3.3 :

Investigation 3.3 Read # 1 – 4 in the investigation.
Be looking for three things:
materials you will need
independent variable
dependent variable
In your lab notebook, record:
the materials needed
the ind v
the dep v

Investigation 3.3 :

Investigation 3.3 Now, read # 5 – 7
Be looking for:
what you will be doing differently in this part of the lab
how you will make measurements
Go back to your materials list and add the necessary new materials

Investigation 3.3 :

Investigation 3.3 Create two data tables – one for each type of drop. Be sure to fully label the tables:
columns
rows
title
units

Energy and Work :

Energy and Work Look over your lab data and the original question of the lab, “How does an air bag protect you in an accident?”
After completing the lab, is there anything you can add to your original ideas?

Good Afternoon! :

Good Afternoon! Today we will:
discuss how air bags work
take some notes
solve energy & work problems
answer the question, “How do air bags decreases the severity of damage in a car crash?”
Please do before the tardy bell:
pick up a whiteboard and a dry erase marker
get out your spiral and something to write with
get a textbook (your own, not shared)

Warm-Up Part 1 :

Warm-Up Part 1 In today’s lesson, we are going to be talking about two physics concepts we talked about before winter break:
kinetic energy
work
You have three minutes to find and write down in your notes the definitions and formulas for each

Warm-Up Part 2 :

Warm-Up Part 2

Effect of Drop Height on Egg Damage :

Effect of Drop Height on Egg Damage size of cracks (cm) drop height (cm) 3 1 2 4 8 12 16

Objectives/Goals :

Objectives/Goals By the end of the day, you will:
1. Relate kinetic energy to the work required to stop an object.
2. Understand the relationship between the force of an impact and the stopping distance.
3. Write a conclusion that uses scientific language to answer the question, “How does cushioning decrease the severity of the damage in a car crash?”

Kinetic Energy :

Kinetic Energy Before winter break, we learned about kinetic energy.
Review: What is kinetic energy?
the energy of a moving object
KE = 0.5 mv2

Kinetic Energy Review :

Kinetic Energy Review Objects in motion have kinetic energy.
KE = ½ mv2
If mass is increased, what happens to KE?
it increases
If velocity is increased, what happens to KE?
it increases

Kinetic Energy & the Egg Drop :

Kinetic Energy & the Egg Drop True or False:
The egg that dropped on the hard surface broke sooner because it had more kinetic energy.

Which Egg had the greater KE? :

Which Egg had the greater KE? The eggs had approximately the same mass.
Both eggs were dropped from the same height.
What do we know about the velocity they hit their respective surfaces with?
because gravity acts on all objects equally, the two eggs had the same velocity when they struck their respective surfaces

Revisit: Kinetic Energy & the Egg Drop :

Revisit: Kinetic Energy & the Egg Drop True or False:
The egg that dropped on the hard surface broke sooner because it had more kinetic energy.
False – the eggs have the same kinetic energy, so kinetic energy cannot be the reason one broke and the other did not

Which Egg had the greater KE? :

Which Egg had the greater KE? The eggs had the same kinetic energy (when dropped from the same height)
So why did one egg break and the other didn’t?

Work & Kinetic Energy :

Work & Kinetic Energy read pg 279 – 281
Focus Questions:
What must be done to change the kinetic energy of an object?
What is a safe way to “get rid of” the kinetic energy of a car?
What is an unsafe way to “get rid of” the kinetic energy of a car?
7 minutes

The Physics of Cushioning :

The Physics of Cushioning In order to stop an object with kinetic energy, work is done.
Do you remember the formula for work?
Work = force x distance
The work done to bring an object to a stop is exactly equal to the amount of kinetic energy the object has

The Physics of Cushioning :

The Physics of Cushioning Work can also increase the kinetic energy an object has.
Whether work increases or decreases kinetic energy depends on the direction the work is applied from and the direction of the object that is moving.

The Physics of Cushioning :

The Physics of Cushioning Bottom Line:
the amount of work done on a moving object is equal to the object’s change in kinetic energy
We represent this relationship with a formula:
W = ΔKE

Check Yourself :

Check Yourself A rolling bowling ball has 1000 joules of kinetic energy. After a certain amount of work is done to the bowling ball, it has 300 J of kinetic energy.
How much work was done?
700 J

Check Yourself :

Check Yourself Our first objective today was:
relate the energy of a moving object to the amount of work needed to stop the object.
Explain to your table partner how work done on an object and the object’s kinetic energy are related.
Take five minutes to write down your ideas about the relationship in your notes. Be sure to give a title!

Bringing an Object to a Stop :

Bringing an Object to a Stop How much work is needed to stop an object with 3000 joules of kinetic energy?
3000 joules (newton-meters) of work
How much work is needed to stop an object with 1500 joules of kinetic energy?
1500 joules (newton-meters) of work

Bringing an Object to a Stop :

Bringing an Object to a Stop How much work is done to stop an object with 500 joules of kinetic energy?
If you apply 100 N of force to stop this object, how far will it travel before it stops?
Hint: remember the formula for work

Mathematical relationship between work and kinetic energy :

Mathematical relationship between work and kinetic energy

Mathematical relationship between work and kinetic energy :

Mathematical relationship between work and kinetic energy Draw this table in your notes and fill in the blanks

Mathematical relationship between work and kinetic energy :

Mathematical relationship between work and kinetic energy Draw this table in your notes and fill in the blanks

Check Yourself :

Check Yourself Look back in you notes where you jotted down your ideas about how work and kinetic energy are related.
Now add specific mathematical example to your list? (Do your own math, don’t just copy from the table!)

The Physics of Cushioning :

The Physics of Cushioning If you look back on the table you just created, you’ll see that as long as kinetic energy remains constant, the smaller the stopping distance, the larger the force.
We saw this in the egg drop lab: the stopping distance in the flour was the indentation in the flour.

The Physics of Cushioning :

The Physics of Cushioning re-read pg 281 in your textbook
focus on what an air bag does in a crash
3 minutes

The Physics of Cushioning :

The Physics of Cushioning An air bag works by increasing the stopping distance of your face and chest in a car crash.
Increased stopping distance means there will be a decreased force. When we are talking about your face and chest, this is a good thing.

Objectives/Goals :

Objectives/Goals Our second objective today was:
demonstrate an understanding about the relationship between the force of an impact and stopping distance
If the kinetic energy of two cars is the same, and Car A has 1000 N of force applied and Car B has 3000 N of force applied, which car stops in a shorter distance?
Car B – because it has a greater force applied

Time to Throw an Egg! :

Time to Throw an Egg!

Relationship between kinetic energy, force of impact and stopping distance :

Relationship between kinetic energy, force of impact and stopping distance True or False
If stopping distance is held constant and kinetic energy is increased, the force of the impact will increase.
True – since the change in kinetic energy is equal to the work done (w = fd) and distance is held constant, increasing the work done (because kinetic energy was increased) means force will increase as well.

Relationship between force of an impact and stopping distance :

Relationship between force of an impact and stopping distance Copy down these sentences and finish them in your notes:
If kinetic energy is held constant, the greater the stopping distance…(what happens to force of impact?)
If kinetic energy is held constant, the force of an impact increases when…(what happens to stopping distance?)

Relationship between force of an impact and stopping distance :

Relationship between force of an impact and stopping distance Copy down these sentences and finish them in your notes:
If kinetic energy is held constant, the greater the stopping distance…the less the force of impact.
If kinetic energy is held constant, the force of an impact increases when…the stopping distance is decreased.

Final Check Yourself :

Final Check Yourself The main objective of this lesson:
Write a conclusion that uses scientific language to answer the question, “How does cushioning decrease the severity of the damage in a car crash?”

How does cushioning decrease the severity of the damage of a car crash? :

How does cushioning decrease the severity of the damage of a car crash? On a clean, whole sheet of paper, copy down this question and answer it fully using scientifically accurate language.
you may find it helpful to create a concept map or organize your thoughts with a graphic organizer

How does cushioning decrease the severity of the damage of a car crash? :

How does cushioning decrease the severity of the damage of a car crash? Proficient answers will include:
evidence that you can relate the energy of a moving object to the work needed to stop the object
evidence that you understand the relationship between the force of an impact and the stopping distance
scientific language

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