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. Put the correct answer here including the letter designation. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Which is greater, the force on the bug or the force on the bus? A situation to ponder… CHECK YOUR NEIGHBOR Which is greater, the force on the bug or the force on the bus? A. Bug. Bus. Both are the same. Cannot say. C. Both are the same. 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 Put the correct answer here including the letter designation. 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. Yes. Yes, but only if both they push equally. No. No, because one of them is Chuck Norris and the rules of physics do not apply to him. A. Yes. 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? A. Yes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley

What does the scale read? Newton’s Third Law of Motion CHECK YOUR ANSWER What does the scale read? A. Yes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley

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

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 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….   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. A. Yes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Calculate the acceleration of the cages 0.2kg 100 Kg 7000 Kg Mu = 0 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Calculate the tension in the ropes FT2 FT1 2500 N 0.2kg 100 Kg 7000 Kg Mu = 0 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? A) F3,4 B) F4,3 C) F3,2 D) F4,3+2+1 1 2 3 4 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Answers Slide 2 = C. both are the same b/c 2nd law Slide 4 = false 3rd 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 3rd 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 Slide 8 = C. Pluto 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 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 = 800N The tree pulls back as hard as the guy pulls forward Slide 11 = 800 N 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 14 = a = Fa/mtotal = 2500N / 7100.2kg = 0.35 m/s2 Slide 13= C b/c 3rd law Slide 14 = a = Fa/mtotal = 2500N / 7100.2kg = 0.35 m/s2 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/s2 = 0.07 N What is the contact force between the chimp’s cage and the elephant’s cage? Fc,e = mm+Ca = 100.2 kg * 0.35 m/s2 = 35.07 N Slide 15 = FT1 = mma = 0.2 kg * 0.35 m/s2 = 0.07 N FT2 = mm+ca = (100 kg + 0.2 kg) * 0.35 m/s2 = 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 (F3,4) so the reaction to that is F4,3 Slide 19 = C & D Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley