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HW Due Place both in In Box (POGIL page 2…… and the worksheet) HW Worksheet – given out at end of class Quest Jan 23 (B day) ***There is a REALLY GOOD review PowerPoint on my website…*** Do 1.Take one and complete BOTH Now SIDES. May work with peers. A bug and the windshield of a fast moving car collide. Tell whether the following statements are true or false, and EXPLAIN your reasoning: a. The forces of impact on the bug and on the car are the same size. 1. 2. 3. 4. True False Not enough info Not quite sure TRUE! FORCES COME IN PAIRS! A bug and the windshield of a fast moving car collide. Tell whether the following statements are true or false, and EXPLAIN your reasoning: b. The impulses on the bug and on the car are the same size. 1. 2. 3. 4. True False Not enough info Not quite sure TRUE! SAME FORCE, SAME CONTACT TIME A bug and the windshield of a fast moving car collide. Tell whether the following statements are true or false, and EXPLAIN your reasoning: c. The changes in speed of the bug and on the car are the same size. 1. 2. 3. 4. True False Not enough info Not quite sure FALSE! COMMON SENSE…DO YOU NOTICE THE CAR SLOW DOWN? DOES THE BUG NOTICE A CHANGE? A bug and the windshield of a fast moving car collide. Tell whether the following statements are true or false, and EXPLAIN your reasoning: d. The changes in momentum of the bug and on the car are the same size. TRUE! 1. 2. 3. 4. True False Not enough info Not quite sure m Δv = m Δv’ Not to mention, Impulse = change in momentum, and we already determined they have the same impulse… Bug Ft m Windshield Ft Δv m Δv •Same Impulse •Same change in momentum •Diff. masses and velocity changes! Does a larger force always produce a larger impulse on an object than a smaller force? Explain. No – not always!! 1. 2. 3. 4. t Yes F = Ft No (1 N) (100s) = (10 N)(5s) Not enough info 100 Ns = 50 Ns Not quite sure YES/NO:____ EXPLANATION: A fully dressed student with a backpack is at rest in the middle of a pond on perfectly frictionless ice and must go to shore. Can this be accomplished? Use KEY TERMS to explain: 1. 2. 3. 4. Yes No Not enough info Not quite sure Yes – throw the backpack! Force = Force, Impulse = Impulse HW – that was due today (workseet) • Worksheet • Texts open if needed • 3 minutes to review with peers in the FRONT of the classroom – Gossiping/ being off task will result in you going back to your seat and will guarantee the teacher will call on you. • Then, we are rapidly popcorning! QUESTIONS ABOUT… • 24 or 26? • A bicycle has a momentum of 24 kg•m/s. What momentum would the bicycle have if it had … • a.… twice the mass and was moving at the same speed? TWICE as much! mv=p . 4 6 = 24 So…. 8 . 6 = 48 • A bicycle has a momentum of 24 kg•m/s. What momentum would the bicycle have if it had … • b.… the same mass and was moving with twice the speed? TWICE as much! mv=p . 4 6 = 24 So…. 4. 12= 48 • A bicycle has a momentum of 24 kg•m/s. What momentum would the bicycle have if it had … • c.… one-half the mass and was moving with twice the speed? Same! mv=p . 4 6 = 24 So…. 2 . 12 = 24 • A bicycle has a momentum of 24 kg•m/s. What momentum would the bicycle have if it had … • d.… the same mass and was moving with one-half the speed? HALF as much! mv=p . 4 6 = 24 So…. 4. 3= 12 • A bicycle has a momentum of 24 kg•m/s. What momentum would the bicycle have if it had … • e.… three times the mass and was moving with one-half the speed? 1.5 times as much! mv=p . 4 6 = 24 So…. 12 . 3 = 36 • A bicycle has a momentum of 24 kg•m/s. What momentum would the bicycle have if it had … • f.… three times the mass and was moving with twice the speed? 6 times as much! mv=p . 4 6 = 24 So…. 12 . 12 = 144 Recap • Last class, we talked about impulse changing momentum. • This class (and the next 2 classes), we are going to talk about what happens if that impulse occurs during 2 scenarios: – When bouncing occurs – When a collision occurs POGIL from last class – 10 minutes • Take out your notes from last class and go to the demo section. (Nerf Guns, Ping Pong Balls, Toppling) • You will be shown the Nerf Gun and Toppling Demos, and you will get to try the Ping Pong Demos. • BEFORE THAT…. I want you to consider the following question (write & answer in your notes) – Would a head-on collision between two cars be more damaging to the occupants if the cars stuck together or if the cars rebounded (bounced) upon collision? (Assume the time of the collision is the same.) Would a head-on collision between two cars be more damaging to the occupants if the cars stuck together or if the cars rebounded (bounced) upon collision? (Assume the time of the collision is the same.) 1. When the cars stick 2. When the cars bounce 3. Doesn’t matter either way 4. Not sure! POGIL from last class • Cross out pages 3 – 4 … look like this: unless you want to challenge yourself to try what the Geo kids are doing…then, feel free to try them at home and check! POGIL from last class – 10 minutes 1. You will be shown the Nerf Gun and Toppling Demos, and you will get to try the Ping Pong Demos. 2. Then, working in the FRONT of the classroom, you MUST answer all questions A through F 3. Please review your HW on the POGIL (page 2) – • Ensure that EVERYONE understands not only WHAT the solutions are, but WHY they are what they are…you should be able to transfer your thought process to other questions regarding similar concepts. ***NOT SURE/ QUESTIONS? ASK A TEACHER!!!*** 1. Finish part G – Conclusion. 10 minutes to complete! When is impulse larger? (heads down hands up) 1. When objects bounce 2. When objects don’t bounce 3. Doesn’t matter either way 4. Not sure! Bouncing • Impulses are greater when bouncing takes place • Ft = ∆(mv) • Falling flower pot hits your head – Momentum stops • Falling flower pot hits your head and bounces off – Momentum is reversed. • **Impulse to stop < impulse to “throw it back again”** – 2(∆mv) – Karate chop – Pelton wheel Bouncing Think about a bouncing ball: Before it hits the ground: Speed = v Momentum = mv At the moment it hits the ground: Speed = 0 Momentum = 0 Impulse needed to stop the ball = mv After it leaves the ground: Speed = v Momentum = mv Impulse needed to accelerate the ball upwoard = mv Total Impulse = 2mv Important point: It only takes an impulse of mv to stop the ball. It takes twice the impulse (2mv) to make it bounce) Just like the medicine ball exercise!!! If the time of impact is long, the force will be milder. If the time is very short, the force is powerful. When things bounce off an object after hitting them, it is even more deadly in force magnitude. A rebound is a special type of collision involving: A rebound is a special type of collision involving: a direction change which results in a velocity change. A rebound is a special type of collision involving: a direction change which results in a velocity change. Observe that the greater the rebound effect, the greater the… A rebound is a special type of collision involving: a direction change which results in a velocity change. Observe that the greater the rebound effect, the greater the… acceleration, momentum change, and impulse. A rebound is a special type of collision involving: a direction change which results in a velocity change. Observe that the greater the rebound effect, the greater the… acceleration, momentum change, and impulse. The result of the direction change is a large velocity change. HW – that was due last class • #11-13, p. 100 • Texts open if needed • 3 minutes to review with peers in the FRONT of the classroom – Gossiping/ being off task will result in you going back to your seat and will guarantee the teacher will call on you. • Then, we are rapidly popcorning! HW – that was due last class • #11-13, p. 100 • Texts open if needed – we are rapidly popcorning! • 11a) Visualize yourself on a skateboard. When you throw a ball, do you experience an impulse? Yes – push the ball, and ball pushes you (force) for an amount of time…force x time = impulse! HW – that was due last class • 11b) Visualize yourself on a skateboard. When you catch a ball, do you experience an impulse? Yes – push the ball, and ball pushes you (force) for an amount of time…force x time = impulse! HW – that was due last class • 11c) Visualize yourself on a skateboard. When you catch a ball, and then throw it back, do you experience an impulse? Yes – push the ball, and ball pushes you (force) for an amount of time…force x time = impulse! HW – that was due last class • 11d) Visualize yourself on a skateboard. In which of the scenarios do you experience the largest impulse? Catch and throw – it’s 1. Catch like bouncing! More 2. Throw velocity change, so 3. Catch an throw more momentum change, so more 4. Same in all impulse! HW – that was due last class • 12) Why is more impulse delivered when bouncing occurs? More velocity change, so more momentum change, so more impulse! Go to your test seats… • • • • Normal quiz procedures apply Open notes, not open books No calc needed… cell phones OUT and SILENT When done, quiz in basket upside down and you may continue working on your HW – (make your hypotheses and try them) • Open notes quest on Ch. 7 on Jan. 23 HW – that was due last class • 13) Why is the Pelton wheel an improvement over a wheel with flat blades? Go to your test seats… • • • • Normal quiz procedures apply Open notes, not open books No calc needed… cell phones OUT and SILENT When done, quiz in basket upside down and take a copy of your: 1. “Momentum Conceptual review” (HW) • Start working on this – it is HW!!! 2. And “Midterm Information” • Read the “Midterm Information” sheet tonight – we will answer any questions about it next class