Do Now

1. HW:Prep for your QUEST next class! Do Now • Take back your quiz • I can guarantee you will see these questions again (midterm, Quest, etc.) • Go through your HW, notes (Do Now’s, Exits, POGILs, etc) and HIGHLIGHT where you can find the solutions to every one of your quiz questions (for the majority of them, it’s word for word) • As you are highlighting, MAKE CORRECTIONS. • Check in with me when you are stuck.

2. ID NAME DATE “Ch 7 Quiz” 1. Scale of 1 to 5 (1 being the least) how confident are you for next class’ Quest? EXPLAIN 2. Reflect after getting back your quiz: did you make silly errors? Did you focus in class? Did you put your full time and effort into your HW (BOTH the reading/ studying AND written?) Were you prepared? Etc…. Give me COMPLETE, HONEST feedback regarding your thoughts (not simply “yes” or “no” answers….full sentences!!!)

3. When is impulse larger? (heads down hands up) • When objects bounce • When objects don’t bounce • Doesn’t matter either way • Not sure!

4. 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

5. After it leaves the ground: Speed = v Momentum = mv Before it hits the ground: Speed = v Momentum = mv At the moment it hits the ground: Speed = 0 Momentum = 0 Impulse needed to accelerate the ball upwoard = mv Impulse needed to stop the ball = mv Total Impulse = 2mv Bouncing Think about a bouncing ball: Important point: It only takes an impulse of mv to stop the ball. It takes twicethe impulse (2mv) to make it bounce) Just like the medicine ball exercise!!!

6. 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.

7. The “physics” term for BOUNCE is REBOUND

13. HW – that was due last week • #11-13, p. 100 • Texts open if needed • PAY ATTENTION as we rapidly review! (need to conserve time with the snow day!)

14. 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!

15. 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!

16. 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!

17. HW – that was due last class • 11d) Visualize yourself on a skateboard. In which of the scenarios do you experience the largest impulse? • Catch • Throw • Catch and throw • Same in all Catch and throw – it’s like bouncing! More velocity change, so more momentum change, so more impulse!

18. 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!

19. HW – that was due last class • 13) Why is the Pelton wheel an improvement over a wheel with flat blades?

20. Question Why is falling on a floor with more give less dangerous than falling on a floor with less give? The floor with more give allows a greater time for the impulse that reduces the momentum of the fall. A greater time for changing momentum means less force.

21. Question What are two ways that crumple zones in cars minimize the effect of force in a collision? • Crumpling increases the time over which the momentum is changed, thus decreasing the force. • Crumpling means less likely to rebound, thus less impulse.

22. Question 2 cars are involved in a collision. Which would be more damaging - if the cars collide and bounce or collide and crumple? Collide and bounce. The momentum change is larger and therefore there is a greater impulse and greater force.

23. Free Write… • I am going to show you a series of scenarios, and tell you whether they are considered to be ‘elastic’ or ‘inelastic’ collisions • It is your job to write/draw the scenarios you see on your T chart • Then, comparing your columns, I want you to create a definition for “elastic collision” and “inelastic collision.”

24. Examples • Remember, WRITE/DRAW what you observe with enough detail to know what’s going on later when you look at these notes! • Newton’s Cradle – elastic • What happens if I release…1? 2? 3? 4? 1 &1? Etc. • Bouncy Ball – elastic • Glob of putty- inelastic • Notice what happens to the side of the putty that is dropped onto the desk… • Cars with Velcro facing- inelastic • Notice what happens if… one is at rest, and one is moving toward the other….or, both move toward each other… • Cars with magnets facing- elastic • Notice what happens if… one is at rest, and one is moving toward the other….or, both move toward each other… • Billiards (pool) – elastic • Car crash - inelastic

25. Create your definitions!

26. Volunteers to share your definitions?

27. Elastic Inelastic • Bounce • Not deformed after collision • Don’t Bounce • Stick • deformed after collision • Need a FORCE to get them back to normal

28. Key Point? and INELASTIC collisions Momentum is ALWAYS conserved, in both ELASTIC

29. What does CONSERVED mean? • Stays the same • Doesn’t change Total Momentum BEFORE collision = Total Momentum AFTER collision

30. Momentum is a conserved quantity in physics. This means that if you have an object or several objects in a system, interacting with each other, but not being influenced by any forces from outside of the system, then the totalmomentum of the system does not change over time. 11

31. Law Of Conservation Of Momentum In the absence of an external force, the momentum of a system remains unchanged. The momentum lost by an object in a closed system will be gained by other objects so that the total momentum will remain the same in the system. Closed System: No matter or energy is allowed to enter or leave the system.

32. The separate momenta of each object within the system may change. One object might change momentum, while another object changes momentum in an opposite manner, picking up the momentum that was lost by the first.

33. In hockey…Momentum is transferred from the stick to the puck. The momentum lost by the stick is equal to the momentum gained by the puck. The total amount of momentum stays the same. Or…Momentum is transferred from player to player. (The momentum lost by one player is equal to the momentum gained by the other. The total amount of momentum stays the same.)

34. EXAMPLE: Cars with velcro demo The first car has a certain amount of momentum (mv) Using numbers… (1 * 1) = 1 After collision, the MASS doubles….and the velocity halves… (2m * ½ v) Using numbers… (2 * ½ ) = 1 But still the same TOTAL momentum!

35. Total Momentum BEFORE collision = Total Momentum AFTER collision

36. We are going to try one together…

39. From now until the end of class… • Finish the BACK of the worksheet you just received • Check in with us when you are done (NOT reviewing as a class) • Meet in pairs or groups to REVIEW the HW that was due today • Check in with us regarding any questions