Newtons Third Law of Motion A situation to

A situation to ponder… CHECK YOUR NEIGHBOR Which is greater, the force on the

Newton’s Third Law of Motion A situation to ponder… When Chuck Norris does a

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR Two “people” of equal mass on

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR How hard must the hand be

Newton’s Third Law of Motion CHECK YOUR ANSWER What does the scale read? Copyright

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR You would have the largest mass

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR If all moving things (trucks, trains,

Guy vs Tree Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Guy vs Guy Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Guy vs Chuck Norris ∞ Copyright © 2008 Pearson Education, Inc. , publishing as

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR A ping pong ball launcher is

Calculate the acceleration of the cages 2500 N 0. 2 kg 100 Kg Mu

Calculate the tension in the ropes FT 1 FT 2 2500 N 0. 2

What makes an action-reaction pair? • • Act on diff objects (Steve the Horse

Action reaction • There is a yogi (in lotus pose) on his recycled yoga

Other action reaction • There are 4 boxes. They are being pushed on from

Answers • • • Slide 2 = C. both are the same – b/c

• • Slide 13= C – b/c 3 rd law Slide 14 =

Slides: 19

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Newton’s Third Law of Motion A situation to ponder… Consider a high-speed bus colliding head-on with an innocent bug. The force of impact splatters the unfortunate bug all over the windshield. Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

A situation to ponder… CHECK YOUR NEIGHBOR Which is greater, the force on the bug or the force on the bus? A. B. C. D. Bug. Bus. Both are the same. Cannot say. Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Newton’s Third Law of Motion A situation to ponder… When Chuck Norris does a pushup, he's pushing the Earth down. True False Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR Two “people” of equal mass on slippery ice push off from each other. Will both move at the same speed in opposite directions? A. B. C. D. Yes, but only if both they push equally. No, because one of them is Chuck Norris and the rules of physics do not apply to him. Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR How hard must the hand be pulling up in order for the scale to read 5 N? Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR You would have the largest mass of gold if it weighed 10 N on… A. B. C. Jupiter Mercury Pluto Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR If all moving things (trucks, trains, cars, cats, Chuck Norris, busses, rickshaws, bicycles ridden by circus bears) on the planet moved East, the day would get A. B. C. Slightly longer Slightly shorter all of the above Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Newton’s Third Law of Motion CHECK YOUR NEIGHBOR A ping pong ball launcher is fired. Compared to the force on the ball, the force is…. A. B. C. D. Greater on the ball Greater on the launcher The same on both Bummer he got fired. He will have to go on welfare. Good thing a democrat is in office. Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

What makes an action-reaction pair? • • Act on diff objects (Steve the Horse story) If A acts on B, then B acts on A Must be acting at the same time Forces depend on each other – Ex: pushing book up w hand = FN increases but weight doesn’t so they don’t depend on each other Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Action reaction • There is a yogi (in lotus pose) on his recycled yoga mat when a butterfly lands on his shoulder. • The butterfly feels the force of gravity pulling her down. What is the reaction force to that? A) The yogi’s shoulder pushing up B) The butterfly pulling up on the Earth C) Air pushing up on the butterfly D) The force of namaste touching everything in the universe Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

Other action reaction • There are 4 boxes. They are being pushed on from the left (red arrow). What is the reaction force to the pink arrow? 1 • • 2 3 A) F 3, 4 B) F 4, 3 C) F 3, 2 D) F 4, 3+2+1 Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley 4

Answers • • • Slide 2 = C. both are the same – b/c 2 nd law Slide 4 = false – 3 rd law says they both push/pull on each other Slide 5 = A. yes – They have equal mass so the same force will result in the same acceleration Slide 6 = 5 N Slide 7 = 5 N – • Slide 8 = C. Pluto – • The tree pulls back as hard as the guy pulls forward Slide 11 = 800 N – • If you walk to the east, you are pushing the earth towards the west which is the opposite of how it spins so you would slow down the spin and lengthen the day Slide 10 = 800 N – • If you can get a scale to read 10 N on a planet with such little gravity as Pluto, then you must have quite the hunk of gold! Slide 9 = A. longer – • 3 rd law says that you need equal and opposite forces. Also, if nothing were pulling backwards, the scale would read zero. So its just like the question on slide 6 If nothing was on 1 side of the rope, it would be slack and the scale would read 0 N. Since you can’t pull harder on one side of a rope than on the other side, each pulls w 800 N. Guy #2 is just like the tree in the pervious question Slide 12 = 800 N – You are only as strong as your weakest link. The guy is going to go flying towards Chuck Norris but the guy can only pull back with 800 N so the max tension in the rope is 800 N so that’s what the scale reads. Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley

• • Slide 13= C – b/c 3 rd law Slide 14 = a = Fa/mtotal = 2500 N / 7100. 2 kg = 0. 35 m/s 2 – Follow up: If you had to stand between 2 of the cages, which ones and why? Get less squished b/t mouse and chimp b/c all you would have to push would be the mouse. In other words, must of the F gets used up pushing the other 2 cages and not much would be left to push on you. – This is called the contact force. – What is the contact force between the chimp’s cage and the mouse’s cage? • Fc, m = mma = 0. 2 kg * 0. 35 m/s 2 = 0. 07 N – What is the contact force between the chimp’s cage and the elephant’s cage? • • Slide 15 = FT 1 = mma = 0. 2 kg * 0. 35 m/s 2 = 0. 07 N – • • • Fc, e = mm+Ca = 100. 2 kg * 0. 35 m/s 2 = 35. 07 N FT 2 = mm+ca = (100 kg + 0. 2 kg) * 0. 35 m/s 2 = 35. 07 N Slide 17 = B; not A because they don’t depend on each other Slide 18 = B b/c pink arrow shows box 3 acting on box 4 (F 3, 4) so the reaction to that is F 4, 3 Slide 19 = C & D Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Addison-Wesley