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Let’s review…

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 ….

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Let’s review…

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  1. 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…

  2. CHANGE in momentum is caused by an IMPULSE • Impulse is a Force exerted for a period of time… it is the PRODUCT of forcex time • Since Impulse equals CHANGE in momentum…. IMPULSE = mΔv = Δp IMPULSE=force x time J =F. t orImp =F. t J =Δp orImp =Δp F. t=Δp orF. t= mΔv

  3. 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= mΔv N. s= kg m s kg m. s= kg m s2s kg m. s= kg m s2s

  4. Based on last class’ pogil…. • Go back to your Do Now • 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:

  5. Comparing throwing at the sheet vs. The hypothetical wall (assume I throw the egg with the same initial velocity) • WALL SHEET • Same 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 = Ft • In 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!

  6. In other words Imp m Δv Δp

  7. Take out your HW that was due last class - POGIL : Part 4 – Momentum Math • Should have finished for HW… any questions? • 800 kg m/s • 360 kg m/s • If you got 360,000, *check your units!!!* Use DA to convert 5000g  5 kg first! • Zero!!! It is AT REST (if it was not at rest, you would need to use DA to change pounds  kg) • 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!

  8. Rank these cars based on momentum before they hit the brakes: • Remember…. m v = p Look at Car A… m = 1000 kg v = 20 m/s Solve for “p” usingmv= p mv = (1000kg)(20 m/s) mv = 20,000 kg m s 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

  9. Rank these cars based on THE IMPULSE needed to stop them • Remember…. Ft = m Δv Look at Car A… m = 1000 kg Δv = v2 – v1 Δv = 0 – 20 m/s Δv = - 20 m/s mΔv = (1000kg)(-20 m/s) mΔv = -20,000 kg m s In other words… -20,000 N s - 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 Most NEGATIVE Most POSITIVE

  10. Rank these cars based on THE FORCE needed to stop them • Remember…. Ft = m Δv Look at Car A… mΔv = Ft -20,000 kg m = Ft s Slight problem…. We don’t know the stopping time! Without ‘t’ we can’t solve for F! Not enough info to solve! Most NEGATIVE Most POSITIVE

  11. Take out your HW THAT WAS DUE TODAYPOGIL : Last page

  12. FOLLOW THROUGH in sports Pulling slingshot back all the way Bending knees when jumping Bungee jumping with elastic Running on asphalt Airbags! Moving hand back when catching Head 1st into brick wall Bungee jumping with rope Run on concrete Moving INTO a punch Karate chop Locked knees when jumping

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

  14. Force x time= Impulse = Change in Momentum = mass x change in vel. -40

  15. 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.

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

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