Thurs Nov 21

1. Forces Test

2. Asst: Guided Notes pages 228-245• Do THESE YOURSELF, they’re

IMPORTANT!

** Note – Momentum is also a SHORT FAST UNIT (because so much is just Concepts derived from Newton’s Laws) – test will be in 2 weeks!

Fri Nov 22 (computer lab???)

**collect any Forces stuff left over** do one of the following …

1. Quick lecture notes on Impulse-Momentum problems & start problems in class

• (do NOT copy list below; they are on your HW packet, with answers!)

– pp. 251-254: #56-60*, 61-62, 64-65, 67-69, 70*, 72a&b&e, 83-84, 85a&b*• *problems with asterisks - 60, 70, & 85 - require unit conversions! • ***#70 is very important!

2. Do Google Slides 1-6 as seen on handout • (do NOT copy notes below; they are all in your HW packet!)

– Make sure you cover ALL the information listed for full credit! You may have MORE slides, but not less.

– Make sure you write out the bk problem, show the work (if there is any), and show the correct answer.

– “C” stands for conceptual problems & you should write the answer in a way that encompasses the question(s).

– THIS IS ALSO YOUR STUDY GUIDE FOR THIS UNIT! (look at the handout, on the middle of the right column, right after slide 13!)

3. Asst: J = F · t = p problems (“asst 3”)

Impulse-Momentum problems1. Write this across the top of your HW paper:

J = F · t = p = pF – pI = mvF – mvI = m(vF – vI) = mv

a b c d e f g

2. List the knowns & unknown of the problem (watch the units in problems with an asterisk!)

3. See what parts of eq to use (note a = g, e = c, etc!) and write only those 2 parts down

4. Plug in knowns

5. Solve for unknown

Question #1 on the test

Let’s do 56& 57 together; see next slide ….

J = F · t = p = pF – pI = mvF – mvI = m(vF – vI) = mv a b c d e f gpp. 251-254: #56-60*, 61-62, 64-65, 67-69, 70*, 72a&b&e, 83-84, 85a&b*p. 870: #1-3

56) m = 0.058 kgF = 272 NvI = 0 m/svF = 62.0 m/st = ?F · t = mvF – mvI

272*t = 0.058*62 – 0.058*0Solve for t ….

57a) p = ?

58b) v = ?

NOTE: If you get stuck tonight, there are some hints on slide 6 of this ppt!!!!

Start working on your own ppt!

Start your ppt:See handout (2013) and/or page 2 of the HW packet

J = F · t = p = pF – pI = mvF – mvI = m(vF – vI) = mv

a b c d e f g

Impulse-Momentum problems hints:

J is the symbol for impulse, p mashed together means “change in momentum” & v mashed together means “change in velocity”

#69b: Use t = the INVERSE of 1.5 x 1023

*******

1.Quick Lecture Notes on the Cons. of Momentum

2.Work on ppts slides 7&8

3.Asst: # 4 - Conservation of Momentum problems

• (Note that problem 86 with the asterisk used to read “an octopus thrown on the ice”! – from the Detroit Redwings…)

• pp. 251-254: #73f, 74e, 75-78, 80, 82, 86*, 87b, 90b&c, 81c&d (Note #76&77 need unit conversions, as they don’t “match”.)

• p. 870 chapter 9: #4-9

Mon Dec 2 (computer lab; hand out HW packets)

PS: Slide 7 could also be about air bags &/or “catching an egg”

Slide 8, bullet 6 should say “If v is bigger for the bounce, then …”

Conservation of Momentum

• “master equation”: p I total = p F total

• This means the total before = the total after• That is the definition of “conservation”, a

question on your next test!• (Recall 2 other sciencey things, that you learned in

chemistry, that are conserved: mass & energy!)

1. Write for EACH problem:• p I T = p F T ( p initial TOTAL = p final TOTAL )

2. ***You do NOT need to write out your knowns/unknowns first; you may plug them directly into this expanded equation as you read:

• m1v1Initial + m2v2Initial + … = m1v1Final + m2v2Final + …

3. Plug in knowns/unknowns for each object, into equation above, for BEFORE the collision.

4. Plug in knowns/unknowns for each object, into equation above, for AFTER the collision.

5. Solve for what you don’t know …

How to solve “Conservation of Momentum” problems:

Just LOOK at the 2 examples at left; you don’t need to copy them down!

Note the units must “MATCH”, like in the gas laws in Chemistry.

So, the masses can be in grams, if they are ALL in grams.

Thus, problems #76&77 (only) need a unit conversion!

EX 1: Car A is 10 kg & going 50 m/s. It rear-ends car B, which is 15 kg & was going 25 m/s. If they stick together, what is their final velocity?

EX 2: Car A is 10 kg & going 50 m/s. It has a head-on collision with car B, which is 15 kg & was going 25 m/s. If they stick together, what is their final velocity?

pI T = pF T ( pinitial TOTAL = pfinal TOTAL )

(m1v1I + m2v2 I + …. = m1v1F + m2v2 F + …)pp. 251-254: #73f, 74e, 75-78, 80, 82, 86*, 87b, 90b&c, 81c&d; p. 870 #4-9

Question #2 on the test

Let’s do #73f & #74e together right now. #75 you can do on your own. But #76 is tricky ….. (see next slide)

p initial TOTAL = p final TOTAL (pI T = p F T )

(m1v1I + m2v2 I + …. = m1v1F + m2v2 F + …)pp. 251-254: #73f, 74e, 75-78, 80, 82, 86*, 87b, 90b&c, 81c&d; p. 870 #4-9

ANSWERS

p initial TOTAL = p final TOTAL

Tricky #76…•Put “projectile” in kg too! (units must match!)

•Note: originally the projectile is INSIDE the launcher, so initial mass = 0.050 + 4.65, and they’re moving at 2.00 m/s together.

•They then split up; projectile is launched with velocity of 647 m/s afterwards.

And start working on your own ppt again!

PS: Slide 7 could also be about air bags &/or “catching an egg”

Slide 8, bullet 6 should say “If v is bigger for the bounce, then …”

NOTE: If you get stuck on any others tonight, there are some hints on slide 15 of this ppt!!!!

p initial TOTAL = p final TOTAL

•Put “projectile” in kg too! (units must match!)

•Note: originally the projectile is INSIDE the launcher, so initial mass = 0.050 + 4.65, and they’re moving at 2.00 m/s together.

•They then split up; projectile is launched with velocity of 647 m/s afterwards.

EQUATION WOULD BE……

ANSWER

Impact Time zzzzzzzzzzzzzzz

J = F · t const, so c

OR

J = F · t const, so c

Catching an egg – tomorrow in class??

Bend legs when land after jumping off desk

Catch hard ball barehanded; bunting

Passing vs spiking in volleyball

Receiving a punch vs karate chopping

Others you can think of?

Slide 7, Question #4

on the test

Note: it is NOT OK to just copy this slide! You must do what the handout says, and use

your OWN examples!!!

Bouncing vs sticking J = F · t = p = mv

Bouncing v bigger (show specific example, using NUMBERS, of why!)

so p bigger so bigger impulse & bigger force#10 (archery) makes wood move faster & farther#12 (bumpers) so more dangerous to passengers *** Discuss rubber bullets on demonstrators …(look at the size of the bruise!)

Sticking v smaller (show specific example using #’s of why!)

so p smaller so smaller impulse & force …

Slide 8, Question #5

on the test

Note: it is NOT OK to just copy this slide! You must do what the handout says, and use

your OWN examples!!!

Conservation of Momentum problems worked out:

Physics Tues Dec 3 (computer lab)

1. Questions on asst 3 or 4; turn in tomorrow

• See next slide(s)

2. Work on ppts slides 9 & 13 using online book to screen capture problems

• see second-next slide

3. Asst: Asst 5 – “Concepts” (all of them) on p3 of the asst packet

• No, they do NOT have to be in complete sentences for the HW! (only for the ppt)

conservation of momentum

To discuss only:

#70:

known is v (=0.63 m/sec)

Check yours to see if that’s what you have!

#4:

note north and south!!!

#8:

both stuck together initially, and at rest!

Any other ones?

Look at Schedules

slides #7 & 16

J = p asst

p I total = p F total asst

Glencoe online textbook:(for slides 9 & 13)

• use Firefox & see webpage for link:– http://www.glencoe.com/ose/

• access code: – EEDF22594B

• Use “PrintScrn” button in upper right of keyboard to screen capture (copy) the screen

• OR …see Shared Classes folder / Out for “Digital Chapter 9” problems & copy the page you want

• “Paste” into MS Paint from either source.• Use toolbar to “cut” from Paint only the problem you want.• You may use your HW to help you; and then turn it in!

– Subscripts in google slides = control comma

Slide 9 & 13 = Questions #1 & 2

on the test

Wed Dec 4 (computer lab)

1. Do 2-D problem #1 together QUICKLY

• Hand out collision pictures• Get out a blank piece of paper, ruler &

calculator• Turn to 2-D instructions in HW packet

2. Work on ppts slides 11 & 12 • whole thing due Friday, printed out • see email about how to finish & how to

print

3. Asst: 2-D asst part 1 (collisions 2-4)

**You MAY also want to work on 5-6 and/or #7, which is extra credit!!!! ALL due Friday.

Lecture NotesHow to solve a 2-D problem!

• See separate Powerpoint for those step-by-step directions!

• The skectehs of the “answers” are also in that ppt (last slide)– Or the very last slide in this ppt too

Thurs Dec 5(last day in computer lab)

1. Turn in anything?2. Review some concepts quickly if haven’t yet

• See slides and/or email and/or webpage about …• Impact Time• Bouncing vs Sticking• Recoil Effect • ppt - help with some questions.ppt – you can look at

this yourself on the webpage!

3. Finish ppts; due printde Friday in class• double-check you have all slides 1-15 done• add slides 14 &15 pics from shaerd google doc• add some pictures• Print out the ppt as “4 slides per page / landscape”

(see email for details)

4. Asst: (A) 2-D collisions 5-6 plus xc7 if you want; (B) finish & print Google slides

Conserved, etc (slide 11)

• “Constant” means that each individual object never changes

• “Conserved” means the TOTAL before & TOTAL after are the same (one object can give some to stuff to another object)

• The impulse-change-in-momentum theorem says J = F t = p.– Thus if F = 0, then J = 0, and p = 0 too, which means the total

momentum does not change. – But, in order for F to be = 0 (and thus pinitial TOTAL= pfinal TOTAL) then the

system must be “closed” and “isolated”• Closed: (just like if I close the door) nothing enters or leaves the

system• Isolated: no EXTERNAL forces on the system (like friction!)

– All of the problems in Asst 4 must have been closed & isolated or we couldn’t have used pinitial TOTAL= pfinal TOTAL!

Slide 11, Question #6

on the testNote: it is NOT OK to just copy this slide! You must do what the handout says, and use

your OWN examples!!!

Recoil Effect #22, etcWho cares if there’s “nothing to push against”?

• By Newton’s third law: • if spacecraft pushes gasses out

backwards, gasses push spacecraft forwards.

• By conservation of momentum: • Total initial momentum equals

zero; • then, total final momentum MUST

equal zero also; • So, if momentum of gasses one

way = 10,000 kg·m/s; • then momentum of spacecraft

other way = 10000 kg·m/s • for a final total of 0 kg·m/s!!

• 8 PTS ON THE TEST, MUST EXPLAIN RECOIL BOTH WAYS TO GET ALL THE POINTS!!!!

Slide 12, Question #7

on the test

Don’t be surprised by the loud noise!

Note: it is NOT OK to just copy this slide! You must do what the handout says, and use

your OWN examples!!!

Cat is example of Recoil Effect too!

**How does the cat conserve momentum? pIT = 0, so pFT must = 0 too ….!?!?

This video reminded me of the cat example with a little twist: http://www.youtube.com/watch?v=O9XtK6R1QAk

Fri Dec 6(back in classroom)

1. “Catch” eggs ???2. Talk about & collect …

• Printed Google Slides• 2D stuff

• Staple your papers all together, with the pictures handout stapled to the bottom; • If you did the extra credit – write me a note VERY CLEARLY on the top of the first

data sheet!• Concepts (don’t take the handouts home; it’s a class set, and we can post them on

the webpage!)• Guided Notes ???? (you’ll get them back Tuesday, when we go over Angular

Momentum)

3. Bill Nye: Momentum (if time start it)

4. Asst: Review worksheet • YES! You may write on it! • Both sides due Mon!! • Note: you’ll be working on the experiment write-up Tues & Wed

evening; the test is on Thursday

Guided Notes Review(then collect)

9) … But when it comes time to USE the Impulse-Momentum theorem, we will expand it out into all its parts: J = F · t = p = pF – pI = mvF – mvI = m(vF – vI) = mv (***write this on a notecard and start memorizing it ASAP!!!

10) Note that the units of impulse are Newton-seconds (from the formula J = F · t) and that the units of momentum are kilogram*meter/second (from the formula p = m · v).

11)…Because F · t = p, we know how to save lives. If we want to reduce the force on an object, we will make the contact time as long as possible. That’s why we have air bags in cars.

18)…In order for momentum to be conserved, there are 2 conditions that are mandatory. The system has to be both closed and isolated. (Question #6 on the test! Know each defn!)

24) – 25) MEMORIZE THOSE SENTENCES!30) & 31) note we will only do conservation in 2 dimensions with

vectors, not with equations (question #10 of the test)32) – 39) We will go over these next week when we talk about Angular

Momentum (Tuesday), which is question #9 on the test

Mon Dec 9

1. Conservation of Momentum experiment• When finished all items in middle of table• On top of photogate box = labpro & cable,

3x5 cards, spring scale and tape

2. Asst: hand-write: Title, Introduction, Purpose, Materials (see correct page in HW packet)

Tomorrow back in math computer lab to analyze data!

UNIT TEST IS THURSDAY!

Tues Dec 10(computer lab)

1. Go over Angular Momentum (fill in worksheet as we go over it)

2. Discuss Experiment write-up quickly3. Get excel-data template from “Out” folder &

type in data, fill down (email home)4. Go over Review worksheet (in red pen) &

turn in5. Asst: work on hand-written write-up –

Procedure & R&C (leaving a blank for actual results to be filled in later)

Angular Momentum (There are at least 20 points worth of stuff listed here; you only need 7!)

1. Angular momentum does NOTNOT mean things at angles; it means things going in CIRCLES or rotating.

2. For things moving in straight lines … J = F · t = p, which becomes the following for things moving in

circles: Jrotational = · t = L

1. This math statement says that (a) Jrotational, a rotational/angular/circular impulse is caused by (b) · t, a torque

delivered over time, which (c) L, causes the object’s angular momentum to change.

2. Torque is defined to be a rotational/angular/circular force. (open a door, spin the wheelie-chair)

3. Torque has the symbol, , pronounced “tau” and has the units [N·m].

4. Torque can be found by: = r · F , where r stands for the radius of the object, like a door handle’s distance

from the door’s hinges. (It’s more effective to push out on the edge, than close to the hinges!)

5. L stands for the change in angular momentum; angular momentum of an object or system changes if there

is a torque on the object (which happens if the system is NOTNOT closed and/or isolated in a rotational/angular/

circular sense).

6. Just plain ole’ L, or angular momentum, can be found in 3 ways: L = r · p or L = r · mv (where r stands for

the radius of the object,). The units are [kg·m2/s]. Also: L = I · , or “angular mass” · “angular velocity”.

• If the system is closed and isolated in a rotational/angular/circular sense, then since = 0, L = 0 also.

Thus angular momentum is conserved, L initial TOTAL = L final TOTAL, or LI T = L F T,

• Examples: the cat (“angular recoil”), rotating ice-skater & planets around suns (L = I · conserved)

Experiment = Recoil Effect• Any questions on what goes in the Intro?

– See email sent yesterday for more details than handout has

• The point of the experiment was to prove the Conservation of Momentum, specifically the recoil effect:– Total initial momentum equals zero; – then, total final momentum MUST equal zero also; – So, if momentum of cart A = + 10 kg·m/s; – then momentum of cart B other way = 10 kg·m/s – for a final total of 0 kg·m/s!!

• Let’s see if it works ….

Conservation of Momentum data(Go to Shared/Out folder to find this template!)

Wed Dec 11 (copy down both days!)***Did you email your data home yesterday? Need to print out from

Excel & attach to hand-written Experiment write-up1. Hand back papers; Guided notes sheet for tomorrow’s HW 2. Finish going over Review worksheet (in red pen) 3. Go over test structure

• See next 2-3 slides4. More review for test…

• Look at a student’s ppt, AND/OR …• Look at old powerpoint to show.ppt, AND/OR …• Take a look at sample quiz

5. Asst (a): STUDY - Guided Notes, your own PowerPoint slides, Concepts***, Review wksht, Assts 3 & 4 problems (memorize 2 formulas), quiz questions on last slide of Agendas …

Asst (b): Do another 2-D problemAsst (c) finish write-up … Were your cart’s momenta conserved???

Thurs – Dec 121) Test (need protractor & ruler)2) Asst: Guided Notes on work, power, and energy pp: 256-265,

pp 284-301

Review Sheet

• Get out a RED PEN – so we can finish going over the Review sheet (fill-in, mc ??)

• Newton’s Cradle … more examples– 4 from one side?– 1 from each side at same time?– 2 from each side at same time?– 1 from one side + 2 from other?– What about 2 from one + 3 from other?

Momentum Test Structure:• Question 1: a series of Impulse-Momentum problems from

asst 3 (did you note the important ones?)

• Question 2: a series of Conservation of Momentum problems from asst 4 (did you note the important ones?)

• Questions 3-8: Conceptual problems – See the GUIDED NOTES, CONCEPTUAL PROBLEMS

KEY, the REVIEW WKSHT, your own PPT’s!– Newton’s 3 laws & what they become in momentum– general impulse & momentum concepts– impact time short vs long (J = F t , with J constant)

– bouncing/sticking in collisions (KNOW v & p bigger for bounce!!!)

– conservation of momentum concepts; difference between constant and conserved (defn of); where does the momentum go / how is it transferred?

– recoil effect stuff (know how to describe it BOTH ways)

• Question 9: Angular Momentum (see notes sheet)

• Question 10: a 2-d problem for you to doBring a ruler & protractor!

How to solve a 2-D problem!Last question (#10) on the test

• Measure distances & angles

• Calculate velocity & momentum

• Draw start point for momentum vectors

• Draw Ainitial PLUS Binitial

• Go BACK TO START

• Draw Afinal PLUS Bfinal

• Does pinitial TOTAL = pfinal TOTAL ?????

The question before that (#9) says “Tell me anything you know about Angular Momentum.” (6 pts + XC possibilities)

CONCEPTS you should know (but they were all on your ppt – have you printed that out yet? – and we’ve gone over all of them already!):

• If you look at a falling ball, it speeds up, so it is gaining momentum, so its momentum is not conserved.– It speeds up because there is an external force acting on it: gravity.– That means it is not an isolated system.– (Momentum can only be conserved if the system is both closed and isolated.)– OK, so, what is causing the external force?– Well the earth, of course.– OK, define your system to be ball + earth.– As you know from the last unit, if the ball falls down,. the earth moves up (equal and opposite forces).– Similarly, if the ball has downward momentum, then the earth has upward momentum, so that TOTAL the momentum is

CONSERVED if you are looking at both the ball and the earth TOGETHER.• CONSTANT means that thing A's and thing B's velocity and momentum never change.• CONSERVED means thing A can give momentum to thing B (or vice versa) so that the TOTAL momentum is always

the same.– CONSTANT means nothing changes in the system.– ie: thing A has the same velocity/momentum always, thing B has the same velocity/momentum always.– CONSERVED means the TOTAL of thing A and thing B remains the same, but thing A can give momentum to thing B, or vice-

versa.• If the system is BOTH isolated AND closed (know the definitions of those for test) then the impulse equals zero.

– Since J = ft = delta p, if J = o then delta p must ALSO equal zero.– If delta p equals zero for a system, then momentum is CONSERVED.

• You must be able to describe the RECOIL EFFECT in BOTH of the following ways:– By Newton’s third law, if spacecraft pushes gasses out backwards, gasses push spacecraft forwards. (3 points)– By conservation of momentum, say… Total initial momentum equals zero; momentum of gasses one way + spacecraft other way

(which are equal and opposite) equal zero too. (5 points)– Now, the above explanation was for a space craft going forwards when the gasses go back out backwards. On the test you will

have your choice of ANY recoil example to use: a hose, a gun, anything.

How much time is left?(Collaboration Day)

Only 5 minutes, take the very small practice quiz on the next slide! (Grade it at home tonight)

More time?• Look at old powerpoint to show.ppt, AND/OR • Put students’ names in a box (if you want to) &

pull a name at random to view their ppt

Homework: (a) STUDY - Guided Notes, your own ppt, Concepts,

Review wksht, Assts 3 & 4 problems, quiz questions on last slide of Agendas!

(b) finish HAND-WRITTEN write-up … Were your cart’s momenta conserved???****Did you email your data home yesterday, so you can print it out from Excel (not Word, that’s for AP) & attach it to your write-up?

5-minute self quiz (key next slide)

1. Write out EACH of Newton’s 3 laws (in order), and what they become in our Momentum unit.

2. If a thrust of 35 Newtons is used to change the velocity of a 72000-kg craft by 0.63 m/s. How long should the thrusters be applied?

3. A 0.115-kg hockey puck moving 35.0 m/s strikes an octopus sitting on the ice. The octopus has a mass of 0.265 kg. Find their velocity as they slide off together.

Do one where th

ey

do NOT stick

together at e

nd,

but at b

eginning

instead?

1) You should be able to see that on your own ppt that you

printed out 6 slides per page & put in your Physics binder!!

2) m = 72000 kgF = 35 Nv = 0.63 m/st = ?F · t = m v 35*t = 72000*0.63Solve for t ….3) p I total = p F total

0.115*35 + 0.265*0 = (0.115 + 0.265)*vF

Solve for vF ….

NOTE: Momentum is a LOWER CASE p !!!

2D answers

Yeah!

Boo

Yeah!

Boo

Yeah!

Boo

XC

Yeah!

Let’s discuss #7’s two strobe pictures…