Do Now: 1. Walk in silently.

Transcription

1 Do Now: 1. Walk in silently. Follow: ms_kellys_universe (yes you may get your phones out!) Due Next Class: New Vocab Cards Impulse Momentum Delta total count (28) U4.HW1 2. Grab a calculator and any papers 3 questions for today. 3. Graph your Unit 3 Mastery 4. Silently practice your vocab cards

2 U3. Retakes Retakes will be offered Wednesday 3:10 PM Thursday 4:10 PM Friday 4:10 PM You are your own human being. You may decide whether or not you want to take the retake based off your mastery and progress report. However, if at the end of the quarter you are failing and decided not to take the retake, there is nothing I can do for you. Retakes are for up to 100%.

3 SOI : Often times, as energy is used and transformed from one form to another we endure some loss that can be minimized to increase sustainability in our world.

4 By the end of today, IWBAT - Define momentum and impulse and apply the relationship between them to solve problems. Why it matters in LIFE: Part of being a functional human being is being able to understand what s happening in the world around you! Why it matters in THIS CLASS: Our Goal = 80% Mastering today s lesson (focused participation, asking questions, etc) is the first brick that will help us reach our goal for this unit, and eventually for the year

5 TEKS: 6(C) calculate the mechanical energy of, power generated within, impulse applied to, and momentum of a physical system; By the end of today, IWBAT Define momentum and impulse and apply the relationship between them to solve problems. Topic: Momentum & Impulse

6 WHAT IT MIGHT LOOK LIKE ON A TEST:

7 LET S START WITH EVERYDAY LANGUAGE What do you say when a sports team is on a roll? They have.. MOMENTUM! A team that has momentum is hard to stop.

8 MOMENTUM, p (units - kg*m/s) Momentum is mass in motion ; it is the product of the mass and velocity of an object. IT IS A VECTOR! p = m(v) p momentum (kg* m/s) m mass (kg) v velocity (m/s)

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10 EXAMPLE A 2250 kg pickup truck has a velocity of 25 m/s to the east. What is the momentum of the truck? Given: m = 2250 kg v = 25 m/s Unknown: p =? Equation: p = m(v) Substitute: p = (2250 kg)(25 m/s) Solve: p = 56,250 kg*m/s to the east Momentum is a vector quantity, so you must specify both its size and direction.

11 You Try! GP 1, 2, & 3

12 IMPULSE, J (units - N*s) A force applied over a period of time is called impulse. J = F( t) J Impulse (N*s) or (kg* m/s) F force (N) t time (s)

13 EXAMPLE Former welterweight champion Ricky The Hitman Hatton had his punches officially measured on a punching bag that was hooked up to an accelerometer and a force sensor. His punches on average lasted.25 s and had an impulse measured at 980 N*s. How much force did Ricky hit the punching bag with? Given: t =.25 s J = 980 kg*m/s Unknown: F =? Equation: J = F( t) Substitute: 980 kg*m/s = F(.25 s) Solve: F = 3920 N Equal to the apparent weight force of 880 pounds!

14 VOCAB CARDS LIGHTNING ROUND!

15 IMPULSE-MOMENTUM THEOREM Looking at Newton s 2 nd Law: F = m*a Remember, means change or final initial p = p f p i v = v f v i Therefore: J = F( t) = p = m v The impulse, J, that acts on an object is equal to the change in the object s momentum, p.

16 EXAMPLE A baseball player bunts (hits softly) a kg baseball thrown at 43.0 m/s. If the bat exerts an average force of 6500 N on the ball for s, what is the final speed of the ball? Given: m = kg v i = m/s F = 6500 N t = s Unknown: v f =? Equation: F( t) = p = (mv f mv i ) Substitute: (6500 N)( s) = 0.144kg(v m/s) Solve: v f = 12.1 m/s

17 YOU TRY! GP #5 A soccer ball has a momentum of 2.5 kg*m/s. You then apply and impulse of 10 N*s. What is the soccer ball s final momentum? Given: p i = 2.5 kg*m/s J = 10 N*s Unknown: p f =? Equation: J = p = (p f p i ) Substitute: 10 N*s= p f 2.5 kg*m/s Solve: p f = 12.5 kg*m/s

18 You Try! GP 4 So why do airbags & seatbelts save lives? WHAT IT MIGHT LOOK LIKE ON A TEST:

19 IMPULSE-MOMENTUM THEOREM A change in an object s momentum, if kept constant, gives the same impulse every time, however, the force exerted over time can be variable. In both cases, the impulse (change in momentum of each egg) received is the same. However, the average force exerted on each egg is very different. The pillow allows the egg to change its momentum over a longer period of time (time of impact lasts longer) than the other egg.

20 INDEPENDENT PRACTICE! Procedure for IP time: 1) Silent work time 2) Try and solve without notes first! Hierarchy of who to ask 1) Your brain 2) Your notes 3) Ms. Kelly (after you #embracethestruggle)

21 EXIT TICKET 60.0-kg person was in a vehicle that was traveling at 26.1 m/s (about 60 mph) at the moment it hit a concrete wall. The velocity of the person equals that of the car both before and after the crash, and the velocity changes in 0.20 s. a) What is the average force exerted on the person?

22 = ((0.0 kgm/s) (60.0 kg)(26.1 m/s))/0.20 s = N opposite to the direction of motion.

23 ON THE BACK OF YOUR E.T. What was one thing you did really well today? Where is one area where you can improve?