Without you touching me. I cant push on you without you pushing on me. I cant nudge you without you nudging me. I cant interact with you without you interacting with me. And this brings up the law of physics, gang, and whats the name of it . Newtons what . Third law. Newtons third law. The law of action and reaction. I can demonstrate that like this. Im bending my fingers up the most i possibly can. Thats the most i can bend my fingers up. I cant bend them any higher. But if i push them, ah, i can. Lets supposed i push on the podium. Ah, now my fingers are being bent up. Whats bending my fingers up . The podium. Podium. Yeah. Thats the most i can bend them. Would you push my fingers, please . Now my fingers are bent just like before, okay . Whats happening to my fingers, gang . Theyre being pushed on. Isnt that right . Theyre being pushed on, thats why you see them bent up like that right. How bout when i touch the wall over here . Was the wall pushing on my fingers too . A lot of people dont see that. Nonphysics types dont see that but physics type see, hey, man, hes pushing on the wall. And whats the wall doing to him. Pushing back. Watch how i lean. Im leaning on the wall, huh . Okay. Now, everybody say, hey, the dudes pushing against the wall, okay . I call this the wall, okay. Everybody sees the dude pushing against the wall. Physics types see that too. And physics types see Something Else. And what else do physics types see . Check your neighbor, see if youre seating next to a physics type. [student chatter] so whats happening, gang . When i push on the wall, whats the wall do . Pushing on you. Hey, you know something, i cant push against that wall without the wall pushing on me. And this further defines an idea weve been talking about all this time. And thats the idea of force. When you impress a force on something, you tend to accelerate that something, that force were gonna further define. A force is an interaction between one thing and another, always, all the time. A force is an interaction between, in this case, my hand on the wall, if this is a wall. And whats thethatd be the action force, hand on wall, whats the reaction again . Wall on hand. You cant push on something without being pushed back. It cant be done. Heres a couple of blocks. These blocks right now dont interact with one another. But now im gonna attach them with an elastic band. So the big block, when i stretch it, will pull on the little block, okay . Now, which block is pulling . Is the big block pulling on the little block . Or is the little block pulling on the big block . What do you suppose . Check your neighbor. Now watch the blocks. Im gonna let the blocks go and sure enough. Did you see them both move . Thats strange. The more massive block didnt move as much as the little block. I wonder why. Maybe the pulls were different. Maybe the big block is pulling harder on the little block because it didnt move very much. Why dont we make the mass of the little block even more . And what ill do is ill put something ill put some clay on it, okay . Make it more massive, okay . Now, will the little block pull harder . Now, you see they both move about the same. If they did moved about the same, what could you say about the forces that acted in each . Equal. And what can you say about the masses of each . The same. Yeah. Now when i make them unequal masses and i pull, which pulled harder, big one on the little one or the little on the big one . Thats the question for you to think about and check that with your neighbor right now. How many say, they might be different masses, but you know what, theyre both pulling on each other the same . Show of hands. My people, my people, all right, all right. Well, lets test that. Could you do something for me, please . Could you hold this rope . Were gonna have a tug of war here. Okay, helens gonna pull the rope that way and im gonna pull it this way. Now, whos bigger, me or helen . Helen. [laughter] okay, okay, now we pull. Okay, now whos pulling harder . Am i pulling her harder or she pulling me harder . The same. How we pulling, gang . Check the neighbor on that one. What do you suppose . Is she pulling me harder or im pulling her harder . Huh . Equal. Whos pulling harder . Is that so . You used to say im pulling harder because you see the rope moving this way. Thats what you used to say. Remember the old days, when you didnt have that spark called what, begin with a f. Physics. Physics, all right . And now youre getting that spark, right . And now youre starting to see the world a little differently. Lets try this with a couple of scale. Attach this right on here. Okay, now you pull that side and we can measure the force, gang, yeah . And ill pull over here. Now you look to see who pulls harder, me on helen or helen on me . And here we go. How do the readings look, gang . Huh . Which one is harder . How about there . How about there . And what are they, gang . Ss, same same. I cant pull on you any harder than you pull on me, okay . And when i touch you whos touching you . Am i touching her or she touching me . Shes touching my hand, i felt it. From my point of view shes touching me. From her point of view im touching her. Whos touching who . Were touching each other. Thank you, helen. My thumb, my forefinger, theyre pulling on each other. Which is pulling harder, the thumb on the finger or the finger on the thumb . Check your neighbor. Same same. Now i got another question for you, gang. A question maybe you couldnt answer a year ago and a question today you can answer. And you check this when you go home. Check the folks at home and ask the folks this, hey, is the earth pulling on the moon . They say, yeah, its kinda pulling the moon around in orbit, okay. Say, but if you lived on the moon, would you say that the moon is pulling on the earth . Now that moon is kinda small compared to earth, only 1 6 the mass. And what would your parents say, is the moon pulling on the earth . Yeah. What would they say . Lets suppose they say, yes, i think so. Now you say, hey, which pulls with the greatest force, the moon, i mean, the earth pulling on the moon or the moon pulling on the earth . Remember when you werent so sure about a question like that. What if id asked you guys that question a month ago . What would you have said . Now, thats a big earth, honey. Thats a little dinky moon. That gravity of that earth thing pulling that moon right down, right . Oh, maybe the moon pulling a little bit back but how hard back . Check your neighbor now. Which pulls harder . You learning the stuff . Huh, is it kinda fittin, huh . The moon and the earth are pulling on each other in one interaction. And that one interaction, earth pull on moon, moon pull on the you cant have one without the other. Theyre both counterparts of the same interaction, do you see that . We can out that down as a rule. If body a pulls on body b, call that action. And the reaction is body b pulls on body a. Its that simple. Lets put that up here. If action is a pulls on b, a could be the earth. The earth pulls on the moon. How can that be . Unless. Okay . And we call that the reaction. Reaction is justflip switch em around. B pulls on a. Its that simple. You got it . I wanna move across the floor. What i do is i push back on the floor. I push back on the floor with feet. Im pushing the floor this way. If im on a skateboard, just see it move that way, huh. I push back on the floor. What pushes on me . Floor. The floor. If i push back on the floor, honey, the other part of the interaction is the floor push thats why i move. Youre in a Swimming Pool. Youre here. You wanna get there. What do you do . What do you do to the water . You push the water back. When you push the water back, how can you do that without the water pushing you forward . So you push the water back. The water push you forward and [whistles] away you go. You wanna learn how to swim fast . Push as much water back with as much speed as you can. And the more water you push back, the more you push on the water, the more the water gonna push on. You. You. That makes you move. You see a car going down the street, huh . Now, all you see, you see. [imitates traffic] see the cars going down the road. Give some respect to the road because whats happening . The wheels are turning, huh . The wheels are turning. Are the wheels pushing against the road . And which way are they pushing against the road right here . This way, right . So the wheels are pushing the road that way. Thats the road. Now, what does the road do to the wheels . The wheelthe road pushes the wheels this way, and the wheels are connected to the. Car. Car. And so the car then. Moves. Moves. Thats right. Try this with your friends. Youre out there looking at cars go by in the road, right . You say to your friends, whoa, man, look at that road pushing those cars along. True or false . True. True or false . The road pushes the cars along. Come on, hey, you believe that . How many say, sounds right to me. Show your hands. How many says, no way, man. I can understand that wheels pushing on the road, but it stops there. That road dont do any pushing cause the road aint alive. You got to be alive to push. Is that true . Huh . When i was pulling this scale over here, you saw this thing read some readings and you saw helens hand on the other side. Lets suppose, for helens hand, i put it on a hook on the wall, and now i pull it. Couldnt i get the same reading . Whats holding it . The wall is dead. How can a dead wall hold the dead wall not only holds it, it pulls it just as if a hand were there. You cant tell the difference. If youre doing a tugofwar, youd plan a tugofwar with a whole lot of a people. Get a wholethese people here, you guys all pull a rope, huh . And you guys pull the other side, yeah . And you pull it both, both pulling, huh . And whats the tension, say, there if these people here pull with a hundred . What are they and it stays still. What are these guys gonna be holding it with . Hundred. Whats the reading on a scale . A hundred. A hundred. Now, what i do is to take a break and i take a curtain. I put a curtain here and i cut a hole through it, and i put the rope through it. I say, okay. Were gonna do it again, gang. Were gonna do it again, gang. Hey, were gonna play a trick. You guys sit down. I take the rope and i put it on a hook on a wall. Hooked it on there, right . And i say, okay, pull like before. These guys over here, they pulled it just like before, theyre pulling with a hundred, right . Whats the scale reading say here . 100. 200. Yeah, some people say 200. What do we say . 100. 100 . Okay . Okay. A hundred. Whats whats going on the other side . The wall is pulling. Thats right. The walls pulling. Its just as hard as the rope pulling on the wall. Walls pulling . Yeah. This stuffis this stuff hard . This stuff is kinda neat, aint it, huh . You cant have a force without a counterpart. You cant have something pulling on something with, huh, honey, aint that nice . So the wall pulls just as much as a human being. Same same. Question . Whats the tension . The tension would be the force that tends to stretch it. Okay. See, and that tension would be the same all throughout the rope. Even if the rope moves like this, see . Theres still be more. It turns out in a tugofwar, the person to win in a tugofwar is not the one that pulls hardest on a rope because the rope will be pulled on both sides equally all the time. Its the one whos pushes harder against the ground. The one who pushes against the ground harder, see, cause the rope just stand off. The ropes cant cancel out. So if i pushed against the ground the harder, then she pushes against the ground, then ill pull her, and ill win the tugofwar. So with that how can you play a tugofwar on ice with slippery, slippery feet . You pull on the rope and what would you guys do . You pulled towards each other. So no one would go the other way. Do you see do you guys see that . See . See . You ride in your bike. You dont have a 10speed. You cant afford a 10speed, and you got a onespeed. And youre going up a road, and the road is like this. Now, you gonna pump, you gonna go up the road. What do you guys do . Do you how many people sit on a seat and try to pump going up you dont do that. You stand up, dont you . And when you stand up, dont you pull up on the handlebars when you pushed down. Why do you do that . Why . You all do that. You pull up on the handlebar and you push down the pedal. And you go, pulling up, youre all the time pulling up on those handle what are you pulling up on the handlebar for . Why . When you pull up on the handlebar. Youre not pushing against. Against what . Against the bike. Against the pedal and that makes you move better. Aint that neat . [laughter] yeah. Its like this too. I remember, when i was a teenager, man, i was really, really skinny. All my friends weighed more than 100 pounds. All my friends weighed more 100. I was in the 90s and was tall as i am now, like a toothpick, man. And i remember this is scouts honor i remember i used to go into the drugstore and id drink milkshakes. Id do everything i could, you know . And everybody, how come youre not gaining weight . God, im trying like okay, i couldnt do it. And i would go into the drugstore and i would get on a scale and make sure none of my friends are around and put the penny in. [whistles] oh, 94. Will the day ever come . Will the day ever come, okay . Well, one time, im over a friends house. And my friend had a bathroom scale in the bathroom. And i was in the bathroom and looked to make sure that no one look cause im always afraid someone will come by and say, hey, hewitt, you dont even weigh 100. Hey, everybody, you know what, hewitt here dont weigh 100 yet. I was afraid of that, you know . Okay. Anyway, one day, im at a friends house, in the bathroom, hes got a scale. And look, theres no one coming. I step up on a scale, there it was, 94, right . And a friend walks in. And i grab the sink. I grab the sink, okay . I grab the sink and i pull up on the sink. When i pull up on the sink. The scale. Finish it up, finish it up, come on. Come on. Come on. What happens . The sink pushed down on me. Im 103 digits. Im there, okay . Some people get the opposite problem, okay . They weigh too much. Theyre little bit maybe selfconscious about their weight. They walk in. Theres a sink. The sinks still there, yeah . They walked in, oh, there it is, 300. If only they weighed like only 290, right . But 300, and they feel selfconscious. Whats wrong with 300 . Theres 300pound types. Theres 99pound types. Its okay. Its big its one world, aint it . But still, you get a little hung up cause you wanna be like the norm, right . Now, youre a 300poundtype, you walk in and your friends come in, and theyre just gonna look and see the 300, theres the sink. Tell your neighbor what you would do. [laughter] when you push down on a sink, honey. Finish it up. Sink push up. Sink push up on you, make you lighter against the scale, you get a lower reading, okay . You can step and like, look, i weigh zero, okay . [laughs] newtons third law. Newtons third law is not so easy for a lot of people. In fact, back at city college when we used to hire teachers, we would have students come in and so let the teachers perform and do a 10minute gig on the blackboard. And wed always have a student ask the following question cause we wanted to ask a question, which sounded very easy but wasnt. Like if you ask the teacher like, whats the wavelength of theline with a Hydrogen Transition . He could say, oh, i see, its a trick. And he say, oh, i dont know the answer to that, but ill look it up and ill tell you next time, cause thats a kind of question you know were not supposed to know the answer to, right . But we wanted to ask the prospective instructors a question for which they thought they ought to know the answer, like an easy question. And we found a very, very easy question that not many people could answer. And the reason they couldnt answer is cause they didnt have the framework that you guys have right now. And its this first of all, we didnt word the question very nicely. Wed have the students say, hey, when i take an object and i drop it, it falls. Theres a force on it, right . The instructor say, yes, that force is called gravity. Whats the reaction to that force, teach . Anyone want a job at city college . Lets see if theres anyone in this class who can answer that question. Here it is, again, i let go of the clay. Is force acting on it . You saw evidence of that force cause you saw it accelerate. Heres your question if theres a force acting on that, whats the Reaction Force . Hey. Talk it up. Anyone sitting next to someone aint saying anything today . If so, put your hand up and go like this, this person aint talking to me today, honey. Is that right . Is that right . Oh, come on. Okay. Hey, whats the answer . Does anyone happen to know the answer . Whats the reaction to the force of gravity acting pulling down on this . Someone wanna try it . Lee . The ball is pulling the earth up. Right on. Lee, you got a job at city college. You get through here and get your diploma, okay . Thats right. Lets suppose id asked a question like this. When i drop this, the earth pulls downward on the clay. If i phrase it like that, the earth pulls downward on the clay. If you would ask that to a teacher type, the teacher type would say, ah, earth pulls downward on clay, the reaction is the. Check and see if your neighbor knows. Come on, come on. You see, you guys could answer the question this time because the question was phrased properly. Its how a question is phrased that depends a lot on what kind of answer youre gonna get. Thats like the monks who are smoking in the monastery. Theyre not supposed to smoke in the monastery, especially in the prayer room, okay . And so one monk sends a letter to the high bishop and says, is it okay to smoke while were praying . And the high bishop could only say what . No, you cant smoke while youre praying, thats a sacrilege. No smoking. And the other monk sends a letter and says, is it okay to pray while im smoking . Yes, you can pray anytime. Okay . You see what im saying . How you phrase the question depends a lot on what kind of answer youre gonna get, okay . So, again, if i say, the earth pulls down on this, whats this pulling come, come, da, da. And as lee stated the clay is pulling up on the earth. But you see, just asking the question, theres a force on this. Whats the Reaction Force . The question is not phrased so well. Do you see the difference . Oftentimes, when you cant answer questions, its because the questions themselves arent clear. When the question is clear and you kind of know your stuff, then you can kind of pick it up and answer it, yeah . You know when i drop this, its quite evident the force is acting in this because the acceleration is noticeable to us all. Is there really a force pulling upward on the earth . I tell you what, im gonna do it again. Do not check your neighbor. Im gonna ask you to be very, very quiet. Notice that the chair is pushing up on you right now. Can you feel the chair pushing up and youre pushing down, and its evensteven, so were all at rest . But nevertheless, the chair is pushing up, right . Im gonna drop this and see if you dont feel all of a sudden the chair, foop rush up against you a little bit. Try it. How many felt it . [laughter] you didnt feel it. You know why you didnt feel it . Because the mass of this thing is tiny, tiny. Look, heres the idea. Heres the force that pulls this down, huh . And heres the force that pulls the earth up. But how about the accelerations of both . The acceleration of this is simply that force divided by its mass, and that turned out to be 10 meters per second per second. We talked about this before. But how about the force that acts on the earth . The mass of the earth is like this. And when you take that force acting on a humungous mass, you get an acceleration like this. See it . [laughter] its like negligible. And see, you dont sense it. But if the earth was smaller and this more massive in fact, what if this was as massive as a whole world and we held it like this and we dropped it. How far will it go, gang . Will it go all the way down there . Halfway. Itll go halfway. Right. Because if this was a mass of the whole world, then this would come down just as much as the earth would come up and it meets halfway. Aint that neat . Aint that neat . So you can take ideas and stretch them, stretch them, stretch them and they become fascinating. I take a rifle. I fire a rifle. Bam any force act on the bullet . Oh, yeah, honey. You know darn well a force act on the bullet, cause fooom that bullet accelerates humungous acceleration. So you know theres a force in the bullet. Any force kicking back on the gun . Let me ask you a question. Can there be a force on the can the gun exert a force on the bullet without the bullet exerting a force back in the gun . Can it . No. No. Theres an interaction between the gun and the bullet. So gun pushes on bullet, bullet pushes on. Gun. Thats the recoil. You fire a rifle, boom. It comes back and hits your shoulder with a force. How big is that force compared to the force that pushes in the bullet . The same. Same. What would you guys have said about a month ago . Oh, theres only a little dinky force from the gun, honey, a humungous force in the bullet. Aint that right . But you dont say that anymore. You know why you dont say that anymore . Physics. cause you got physics, right. Because you learned in physics. You learned the stuff. You learned it, huh . Youre learning the physics, yeah . The forces are equal and opposite. But you know what . The effects arent. The effects of the force are different, but the forces are the same. You know what this means now . Critical thinking. You have to distinguish between a thing and its effect. Dumb people cant do that and they get in trouble. We can or cant . Were gonna be seeing, okay . Lets look at this. And you fire a rifle. Heres the bullet. Whoosh bullet races out. And the bullet has a force acting on it, but that gun kicks back. How much force . Same. Really the same . Yeah. The same. The same force acting back. Now, the acceleration of the bullet, a lot or a little . The answer begins with an l. A lot. A lot because heres the mass of the bullet. Heres the mass of the rifle. So heres the acceleration of the bullet. Foom but heres the acceleration of the rifle. So the rifle only goes back to here in the same time the bullet goes from here to here. That bullet is accelerating like bunkers, right, inside the barrel. Now, when it gets outside, isilaccelerating . No. No. Now [whistles] it coasts. Weve talked about this before. Its accelerating down thats why it drops before it got right back. But while its inside, the forces are the same but the masses are different, that means that the effects are gonna be different. Wh do you meanhe eect . How much it moves. You see . So that they think it only moves a little bit. The little thing moves a lot and they got the same force. Thats the two blocks that i pulled before. I pulled the massive block and the light block. And they pulled toward each other, but the light block moved a lot. Some people say, oh, theres more force on the light one. And you guys say. Uhuh. Same force, less mass, more acceleration. Now, youre gonna tie all those ideas together force, mass, acceleration. How many people do you know that are good at thinking about three ideas at one time . You hear people say that physics is a tough subject. You know why . Because you gotta think of multiple ideas at once, well, maybe not at once. But you gotta consider multiple ideas when youre asked the question. And whenever i ask you any question about acceleration, theres two ideas youre gonna consider, two. You know what youre friends out in the street gonna consider. How hard is push and pull . But you guys are gonna consider not only how hard is push or pull, but what else . Mass. How much mass you get there. How much mass is being pushed or pulled. And when you consider that also, now you got it together, and thats newtons second law. Okay. And this force here is part of some interaction. Heres the other part. Newtons third law. Yay. Newtons first law, the idea of mass to begin with, huh . Things have mass. They have a tendency to remain at rest. That rifle has a lot more tendency to remain at rest than a little slug of bullet, okay . So the masses are different but the forces are the same. Thats todays lesson. And the accelerations are different, thats last times lesson. You see how all those ideas connect. Its the connection of ideas. So youre traveling in the wrong country at the wrong time and its totalitarian. And theywhat they do is they capture you and they say, hey, we got you, honey, up against the wall. And they put you up against the wall. They handcuff you. You look at the wall. You see all these bullet holes on the wall. You say, oh, no. And they put you up against the wall. And some guy comes out with a great big highpowered rifle, and hes got these little eagles over here and hes got a cap with eagles. You know, eagles are strength or something, okay . And hes polishing his rifle up. Hes just gonna aim at you and do you in. And you kind of look at him and you kind of give him some obscenities, okay . And he says, oh, wait a minute. He says, were not barbarians here. Ill at least give you one last wish. And you say, one last wish . He say, yeah, one last wish. Heres what you might wish. You could say, okay, im guilty of whatever it is, even more than you say. And what i want you to i want you to im not trying to be a wimp out of it. Im not gonna wimp my way out. I want you to shoot me, okay . But i dont want you to shoot me with that little dinky bullet. I want you to shoot me with a humungous bullet, more humungous than the rifle from which its fired. And you, i want you to pull the trigger. Whats gonna happen . [laughter] who is better off, the target or the shooter . Whats gonna happen to that guy when he fires whomphe gonna walk around the rest of his life like this. One of his eagles gone, right . Rockets. First day i was here talking to you guys, i said, how does a rocket move . Remember, we all get in the Swimming Pool together . And we get in the pool, and i push against the edge of the pool, and i rocketed across the pool, right . And i said, is that how a rocket works . And you guys said, yup. Sure is, hewitt, sure is. And i said, nope, it aint. And he says, oh, whats going on . Lets talk about that now. How does a rocket move . What makes a rocket go to the moon . Does it push against the launching pad so hard that it bounces up and just keeps going, going, going, going . Like throwing a ball against super ball against the ground and have it bounce to the moon . Is that how a rocket works . What pushes on a rocket, gang . The gas or something. Its like this gun. That gun is being pushed the opposite to the direction the bullets going, yeah . If i took that gun and i held it down like this and i fired it, would the gun kick up . And after it fires one bullet, i fired another one, would it kick twice . Lets suppose i have a machine gun, honey. And i put that machine gun on like a piece of piano wire. See the piano wire stretched tight here . See . See its nice and tight. Okay. Twang. Now i put that machine gun on a couple of screw eyes, okay . And i take the machine gun, and i pull the trigger. Brrbrrbrr what could happen to the machine gun . Can you guys see it climbing up . Its gonna recoil away from the bullets it fires. The gun pushes the bullet down. The bullet pushes the gun up. Now, a rocket fires bullets, too. Made out of lead . No, molecules of gas. Fires them fast or slow . Fast. With a lot of force or a little force . A lot of force. So those gas particles are fired up. Theyre pushed out, right . So the rocket pushes the gas down. You guys can finish it up. Now you know how a rocket get to the moon. See, people used to think that the rocket pushes against the air. In fact, the father of rocketry, robert goddard, said back in the twenties, hey, gang, the time is coming when the human race will get to the moon with rockets. Not airplanes, rockets. And he was belittled, and he was humiliated by the press. And one press person says, dr. Goddard obviously doesnt know his science. Because if he studies books, hell find out that between here and the moon is a vacuum, and theres no air for the rocket to push against. So a rocket could never travel in a vacuum. And thats what they said. What do you guys think about that . Can a rocket travel in a vacuum . Yes. You know a rocket can travel in a vacuum, cause this is what . This is almost the year 2000. So its the times. But back then, you know, 80 years ago, 70, 80 years ago, people didnt know about these things so much. It wasnt part of the general consciousness. In fact, goddard did this for the press. He did the following experiment. He put a pistol inside a vacuum chamber, and he pulled the vacuum. Chchchchug so theres no air in there. Dropped a little feather, fall just as fast as anything else. A vacuum in there. Then what he did is he had a little mechanism whereby he could pull a little trigger outside, little stick would come out and pull the trigger of the gun. And he showed that when the bullet went down, the gun went. And he says, thats how a rocket works. The bullet doesnt need any air to push against to make the gun go back up. Its straight, straight newtonian physics. Rocket pushes down on gas, gas pushes up on rocket. There you are, and you can go all to the moon if all the way to the moon if you keep pushing. A little story goes with that. You know, human beings went to the moon, 1969. Before 1969, they were talking about going to the moon. My brother had a dear friend, perry hunter, sort of like a scientifictype guy. And perry hunter and my brother used to get in arguments about this whole apollo mission, as to whether or not humans could get to the moon. And i remember, one time, overhearing an argument between my brother dave and perry hunter. And perry hunter was claiming, no way, no way a human being is gonna get in a rocket and get to the moon and come back. No way. Its all press. Its all a farce. Its all hollywood. They cant do that. And my brother says, perry, how do you know they cant do that . And perry said, because im a marksman. And i know what it is to take a riffle and get 200 yards away from a target, and boom, hit that target dead on. I know what that is. And when you talk about going 240,000 miles away, i dont care what kind of high tech they got, theyre not gonna aim that rocket properly. Theyre gonna miss. Perry didnt understand at all how it happens. Gang, they dont aim a rocket to the moon and fire and hope they aimed it right and it hits. Thats not the way it happens. How does a rocket go to the moon . They could never do that without highspeed computers. They fire the rocket in the general direction of the moon. Whooosh now, as the rockets going out, the rocket sights on the stars, sights on the moon, sights around and answers the following question where am i . The rocket can ask that question and answer it. Then the rocket says, whats the best way from here to the moon from where i am, not where i was . From where i am, whats the best path . That path is calculated. Little rocket pushes out on that particular course. Then it go whooosh a little while later, boom. Rocketwhere am i . Okay . Whats the best possible way to get to the moon given where i am . Then, plots a whole new path. It isnt like this one path and if it gets off the course, it tries to get back on. It doesnt do that. It plots a new path all the time. Keep getting closer and closer, closer, plot new paths and follow those new paths, whoop, boom, bullseye. Thats how they do it. So if youre ever, in life, going from one place to another, you say, i wanna go to here. You get off the path. You dont have to get back on the path. What do you do . You say, hey, whats the path, the best path from where i am, not where i was back then when i was 16 or 17 or 18 or whatever like that. So you go by steps. You plot a new path all the time. You take a piece of paper. The piece of paper, you say to the heavyweight champion of the world, hey, champ, do me something, i give you a Million Dollars. Hell say what . Hit this piece of paper with 50 pounds of force. Is he gonna collect the Million Dollar . Get the heavyweight champ of the world to throw his best right hand. Hit that paper. Hit that paper with 50 pounds of force, get a Million Dollars. Can he do it . Can he . Can it be done . No. You cant hit that paper with 50 pounds of force. You know why . You cant get that kind of interaction with that little dinky piece of paper. You cant get it. This paper is not capable of giving you a 50pound interaction. You cant hit this paper any harder than the paper hit back on you. So you cant do it. Thats what gandhi was talking about. You cant be pushed any harder than you push back. Cant do it. Now, take the paper and hold it against the wall. Boom. Can you get 50 pounds on the paper . Oh, yeah, youll get 50 pounds on the paper, okay . Because what youre doing, youre pushing it against the wall now. And the wall can push back with you 50 and squash the paper50, huh . But just on itself, you cant do. Aint that neat . So what are we illustrating here . That you cant exert a force on Something Else unless that force exerts the same amount back on you. Aint that neat . Newtons third law, gang. Yay, you got it . Heres a horse pulling a cart. And on the cart is a farmer over here. Okay. Farmers yelling at the horse, and this carts all loaded up with bags of bananas or something the farmer is gonna bring to town, okay . And now, what the farmer says to the horse is, horse, pull the cart. I wanna go to town. And the horse says, wait a minute. No sense me pulling on the cart. Because if i pull on the cart, the carts gonna pull on me. And if i pull hard, the cart will pull back hard. And however hard the force i exert over here, there be an equal opposite force pulling back this way. The forces will cancel out, so we might as well just stay here. The farmer said, no. Pull, pull, pull. I guarantee, if you pull, well go to town. And the horse said, but i dont see it. Every action, theres a reaction. How are we gonna get to town . How does the system move, gang . Its true that for every action, theres an opposite and equal reaction. Why dont they cancel out and nothing happens . Think about that. Itll make for a good weekend, all right . Okay, physics. Physics. [music]