Let’s review…

HW Due Read 7.1-7.2, Do # 7-10 pg. 100 & Finish POGIL

Tonight’s HW

Read & STUDY 7.1-7.3, Do # 11-13 pg. 100 QUEST Jan 21st or 23rd (date TBD)**Since it is an OPEN NOTES QUEST, no study guide or formulas provided.However, study as if it were CLOSED NOTE!!!

Do Now

1. Put BOTH of your HW assignments TOGETHER in the In Box (stack them together – don’t need to staple)

2. Reviewing test – sharing answer keys, checking, correcting, and understanding WHY the answer is what it is - - need help? See a teacher or peer you trust!

LET’S REVIEW…The following slides contain some

key points you should have learned in LAST CLASS’ POGIL

You will be going BACK to LAST CLASS’ Do Now (EGG TOSS) in a few minutes to explain what actually happened based on ALL you learned so far, so take those out now…

CHANGE in momentum is caused by an IMPULSE

Impulse is a Force exerted for a period of time… it is the PRODUCT of force x time

Since Impulse equals CHANGE in momentum….

IMPULSE = m Δv = Δ p

IMPULSE = force x time

J = F . t or Imp = F . t

J = Δ p or Imp = Δ p

F . t = Δ p or F . t = m Δv

Newton’s 2nd Law is:


Substitute the definition for acceleration:



Rearrange the parentheses




Substitute the symbol p for momentum




Substitute the symbol p for momentum

Move t to the other side of the equation ; impulse equals change in momentum

HERE’S HOW THE UNITS WORK

Since Impulse equals CHANGE in momentum….

So … we can substitute in the units like this:

But remember…the NEWTON is a unit that is shorthand for…

So really, the equation’s units could look like this:

And after cancelling out the ‘s’ in the numerator and denominator:

F . t = m Δv

N . s = kg m s

kg m . s = kg m s2 s

kg m . s = kg m s2 s

BASED ON LAST CLASS’ POGIL….1. Go back to your Do Now2. Using ALL key terms you learned

(force, stopping time, impulse, change in momentum, mass, change in velocity, etc.) please explain WHY the egg did not break when it hit the sheet:

COMPARING THROWING AT THE SHEET VS.

THE HYPOTHETICAL WALL (ASSUME I THROW THE EGG WITH THE SAME INITIAL VELOCITY)

WALL SHEETSame Change in Momentum (m Δv)

Same VALUE of impulse (Ft)(*remember, this is the PRODUCT of force x time)

But DIFFERENT forces & stopping times!

WALL SHEET

Ft = m Δv = FtIn both case, the egg experiences the same momentum change and the

same impulse…

But it experiences MORE force in a LESSER TIME when it hits the wall….

And LESS force in MORE TIME when it hits the sheet!

These all have the

same NUMERICAL

VALUE!

IN OTHER WORDS

WallF t

SheetF t

Impm ΔvΔp

TAKE OUT YOUR HW THAT WAS DUE LAST CLASS - POGIL :

PART 4 – MOMENTUM MATH• Should have finished for HW… any questions?1. 800 kg m/s2. 360 kg m/s If you got 360,000, *check your units!!!*

Use DA to convert 5000g 5 kg first! 3. Zero!!! It is AT REST (if it was not at rest,

you would need to use DA to change pounds kg)

4. Marshmallow: 75 kg m/s Bowling Ball: 40 kg m/s

Mallow wins!*Check your units!!!* Use DA to convert 50g

marshmallow 0.05 kg first!

Rank these cars based on momentum before they hit the brakes:

Remember…. m v = p

20,000 kg m s

10,000 kg m s

10,000 kg m s

10,000 kg m s

20,000 kg m s

5,000 kg m s

F B = C = D A = E

Most NEGATIVE Most POSITIVE

Look at Car A…m = 1000 kgv = 20 m/s

Solve for “p” using mv = p

mv = (1000kg)(20 m/s)mv = 20,000 kg m s

Rank these cars based on THE IMPULSE needed to stop them

Remember…. Ft = m v Δ

- 20,000 N.s -10,000 N.s -10,000 N.s

-10,000 N.s -20,000 N.s -5,000 N.s

A = E B = C = D F


Look at Car A…m = 1000 kg

vΔ = v2 – v1

vΔ = 0 – 20 m/sv = - 20 m/sΔ

m vΔ = (1000kg)(-20 m/s)m vΔ = -20,000 kg m sIn other words…

-20,000 N s

Rank these cars based on THE FORCE needed to stop them

Remember…. Ft = m v Δ

Not enough info to solve!


Look at Car A…

m vΔ = Ft -20,000 kg m = Ft s

Slight problem….We don’t know the stopping time!

Without ‘t’ we can’t solve for F!

TAKE OUT YOUR HW THAT WAS DUE TODAY

POGIL : LAST PAGE

WHAT? HOW? LIST SOME EXAMPLES?

CASE 1

Increase Momentum(usually means velocity increases)

Apply the greatest force for the longest time

CASE 2

Decrease Momentum(usually means velocity decreases)

Minimize forces by increasing stopping time

Maximize forces while decreasing stopping time

FOLLOW THROUGH in sports

Bending knees when jumpingBungee jumping with elasticRunning on asphalt Airbags!

Head 1st into brick wall Bungee jumping with rope

Run on concrete

Pulling slingshot back all the way

Moving hand back when catching

Moving INTO a punch Karate chop

Locked knees when jumping

Force x time =Impulse = mass x velocity= Momentum Change

There are 2 types of algebra problems, combined into one table.

Here are your hints when solving:

• The 3rd and 4th columns are always equal; that is, the impulse is always equal to the momentum change.

• If any two of the first three columns are known, then the remaining column can be computed.

• This is true because the impulse=force • time.

• Knowing any two of the last three columns allows us to compute the remaining column.

• This is true since momentum change = mass • velocity change.

-40

Force x time = Impulse = Change in Momentum = mass x change in vel.

POGIL• Do not use your book… • READ the boxes on the POGIL. Recall prior info, use

your HW, and USE THE BOXES!!!• Check in at stop signs. • You may ONLY USE the computer or a personal device

(iPod, phone, etc.) when the instructions call for it; you may only use the listed site – NOTHING ELSE! Otherwise, computer and group privileges will be revoked for today, and personal devices confiscated.

• Goal is to FINISH THIS TODAY! • Whatever is not finished becomes HW• Stopping w/10 minutes left for an exit

During this time, individual groups will be conferencing w/ a teacher to review your Newton's Laws Tests.

EXIT• Take out your textbook HW form the past 2 nights:• #1-6• And #7-10• We are popcorning – listen, ask questions, make

corrections!

HW

Read & STUDY 7.1-7.3, Do # 11-13 pg. 100 & Finish POGIL from today’s class (up to p.4)

QUEST Jan 17th & 21st, or 22nd & 23rd (date TBD)**Since it is an OPEN NOTES QUEST, no study guide or formulas provided.However, study as if it were CLOSED NOTE!!!

Documents

Let’s review…