Basic Physics Lecture 15

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Basic Physics Lecture 15
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Acceleration Weight Effects unit Sewing Force Order and disorder (physics) Energy level Field-effect transistor Generation Mask Turning Control rod Cardinal direction Forging Rotation Clock face Homogeneous isotropic turbulence Movimento di Studi per l'Architettura home office Sidecar Ground station Cocktail party effect FACTS (newspaper) Direct current Game Gentleman Computer animation Series and parallel circuits Friction Mass Satellite Rotation Level staff Week
Girl (band) Capital ship Acceleration Analog signal Scouting Minute Thermodynamic equilibrium Multiplizität Particle Spant Automatic Block Signaling Electron energy loss spectroscopy Arc lamp Anti-lock braking system Sunday Year Cocktail party effect FACTS (newspaper) Focus (optics) Monday Direct current Rolling (metalworking) Fahrgeschwindigkeit Cartridge (firearms) Mass Rotation Book design Level staff Noise figure Switch Spinning (textiles) Ruler Hot working Cosmic distance ladder Clock Schubvektorsteuerung Electric arc Force Access network Cardboard (paper product) Apparent magnitude Society of Manufacturing Engineers Ship class Alcohol proof Wednesday Spare part Video Nanotechnology Hose coupling Antiparticle Material Mail (armour) Telephone Array data structure Typesetting home office Catadioptric system Winter Naval architecture Electronic component Force Carl August Liner Tuesday Map Hydraulic accumulator Drehmasse Finger protocol Angle of attack Sizing Computer animation Standard cell Relative dating Water vapor Synthesizer Extra-vehicular activity Week Atmosphere of Earth
Paper Cosmic distance ladder Hot working Weight Noise (electronics) Blow torch Day Measurement Force Order and disorder (physics) Cardboard (paper product) Field-effect transistor Apparent magnitude Control rod Schraubenschlüssel Alcohol proof Rutschung Spare part Negation Antiparticle Mail (armour) Electron energy loss spectroscopy Renewable energy Homogeneous isotropic turbulence Paper Ballpoint pen Gemstone Force Year Finger protocol Angle of attack Direct current Spin (physics) Computer animation Standard cell Autumn Ammeter Mass Plane (tool) Trade wind Noise figure Near field communication Atmosphere of Earth Spinning (textiles)
Cosmic distance ladder Sizing Computer animation Thermodynamic equilibrium
Angle of attack Cosmic distance ladder Hot working Computer animation Weight Cartridge (firearms) Rutschung Electronic component Year Force
Cosmic distance ladder Woodturning Combined cycle Short circuit Force Energy level Finger protocol Angle of attack Apparent magnitude Computer animation Hour Mass Book design
Ruler Acceleration Weight Day Minute Microscopy Thermodynamic equilibrium Apparent magnitude Angle of attack Computer animation Cartridge (firearms) Fahrgeschwindigkeit Hour Institut für Raumfahrtsysteme Friction Rotation Relative dating
I think we're gonna get started on the 1st thing I want do is make a quick comment on 1 of the homer problems is the 1st time I received multiple
E-mails about 1 and the question is drawing the free body diagram for the masses are in a situation where we had 1 hanging over the and Napoli and another 1 and in the homework problems this surface was frictionless and MSA was bigger than mass B I forget they did exact numbers are just our ratio of many people miss the following fact They would get The free body diagram for mass and a correct they would draw attention they would draw away and they would draw normal force they get that right And then they Procedure draw free body diagram for mass and they would draw away And they would draw attention and they would try get those 2 about equal I'd failed a little bit there but then they would get a rock with a dry that looked like that's what is wrong with Bakker and drying Besides fact or crooked the can draw straight what's wrong with that dry Mazze is accelerating that both masses are accelerating how do we know that now a member of your back but but Massei is bigger than mask Why does not matter what free body diagram here makes it absolutely Obvious that mass a hostage accelerating Well what this free body diagram makes it completely clear just by looking at the free body diagram that mass a half to be accelerating That there's just as those of force in Directions And there's not anywhere to cancel it so there is a net force and of I have a net force I have Acceleration always and his wife don't usually don't nearly or something more massive so not to move right you have to use that people that nite It is how the world behaves now divide added friction over here so I should say Ed accelerates as attached to be restraining being has to accelerate so the tension has to be less than the way And that's the key piece there now suppose I friction What is the chief feature that a worry about this problem to determine if they NASA's accelerator There's a key physical number that could be very poor in that I need to know these things going accelerator not what number must New West the maximum of the friction can be as less that is Equal to the maximum U.S. times as that of the U.S. is always less than 1 Right That Force of friction will actually be that the weight of mass said and the weight of man as being is pulling on everything so depending how much of a fracture the says And how much bigger This is that it still might accelerate so the that MA for instance is twice and b but Mu say something like . 1 this will still accelerate because the of force but net Force will still be positive yes Factory Susan U.S. here sorry but yet got But Basically that has to do with the fact that I can't generate Larger forces then the weight dude effect on you you back when I say always less so I had to be a little careful because of course there's there's a gray area from where it is considered normal going over to gluing staff right went to boast that you can think of it as forging greater than 1 and so you can imagine some super stupor sticky services where you have a bigger US Army UK but at that point you would attend the started think of it as the things being stuck together But So I was very glad I got those questions echo that really points to I I think 1 of the big misconception run into when things are going over corners on ramps and connected to each other that it's not just the way you have to ask What are the real forces and what direction point Any other questions on that That this week worried of forces we had the normal force friction said wait Tensions and art Where At our Polls there were going ask the question Crime rate Aceh question does where are they Act matter so back to clicker questions to start a software on A now I forgot that In this lecture hall I can access the door were easily that you can see so that is my level demo device here which we think it was a door Here is the hands of the door right and the question is to make it run late or opener close the door Do I push on the end of the door do I pushed a perpendicular are far away from the hinged order I open the door Right I'm etc. weird sideways or write open the door hinges wears attacked the what do I pushed word on the door Like the edge of the door of Thing is that lapses in Milladore do I pushed perpendicular to way I wanna rotated or ignored in the hands and I push on the hit I pushed open door Organized me but there was between into the edge of the door vs. on the face of the door because apparently some of you are having trouble opening doors that 30 per cent of you right now which is not good Take it my doorways hair and open this way this is the face of the door This is the ads of the door I met the person going through the door 5 for our 3 2 1 OK maybe ever seen for sidecar the really old right back there were that the kid is pushing a liberal says poll by those view would be I'm curious how you get in and out of doors not to be insulting here up but If I come up to a door And for satellite best yet at the edited or of Beethoven very well right here at the push or use the door handle right which is on the face of the door and you pull employers on the face of the door we do not close parallel to the thing were trying to rotate the reason for this question is to highlight that if I want to make somethin rug I'll have to worry about Where the forces of flying And the direction the forces applying notice Forces like this are not making his rotate of course like this So the direction and where I applied matters like a of his rod and I push right here Not really getting any rotation When tag So now let me ask you another question Away from the door away from the games in the face of the door now let me draw an object for you
Think of it as I guess that On light So Solana Pfurtscheller surface and the 1st thing I'm gonna as I'm going hit it right at the end there So answer this question of I hit readily and waiters know about clockwise is like that if you've forgotten and counterclockwise is That because I know your use just digital But Around the clock You're iPods and phone so you don't know what clockwise and counterclockwise I know I know that's insulting since all them are analog right you can get We have analog humor back to analog clocks but which wetland happens a Clockwise Bit rotated counterclockwise city and accelerate the object to the right of the right I do you would be both a and C negating the only he would be both a and B But sorry B and vision both be in city that was a type of sorry about that Right Number of Ford's list surface to sit in their life around outer space now is not the end of it where But but but 5 more seconds 4 3 8 2 white Most people are having a rotate And moved or Mallette answer the question again so close I hit Right in the middle OK it does look right in the middle I'll try Get a little bit closer to the middle Where I hit it right in the middle Now what is it deal but to be quicker 10 seconds 13 away this from the runway 9 8 7 6 5 4 3 2 white Excellent Perfect so Pretty much everyone got that right but it right in the middle snuck rotate device that at the end and I meant to bring bring a bigger ruler What will try this year bouncer my finger they'll bounce and figures If I had it It goes up and spit so whatever I hit it will force the matter where I had it what's still moved it still accelerates And the reason for this is very important as we go going the next section we have to realize that all forces do 2 things 1 they And there If they are applied to the center of mass M might talk about a 2nd And cause an acceleration Other setter maps resort we mean by treaty As a point particle and that is what F total It was And a really does for us is really the acceleration of the center of mass so any object weak and that's why we're doing little boxes all last week any object acts like it's all gathered together at center of mass no matter where I apply the force that center of mass move The same way I saw that was actor staff And if I had in the center of I had at the end of the road the exact same right because of the same initial velocity the same acceleration Now Guess So that we're going to have to there in this class we actually do not worry about calculating that we had more time we would also have a the center of mass for everything we have be uniform objects that are perfectly symmetric At the center of mass will be the center of the object so all of your examples that you will be asked to do this week in this section on the exams will have that nice property if you're someone who has not yet taken cats and planned to that may be something you have to look up on your own study that I'm I'm sorry we just don't have time in the 10 weeks to cover It's fairly straightforward mathematically to do not to art but it's not something we do in the class so you just need to know that this is the center of the object and everything we did last week was this part of forces What we're doing now is adding the other feature For an extended object something with But for says Also caused rotation about an axis And the way we talk about this redefining new object called the torque which I have a symbol capital T for the Greek letter talent And it's really the toward that causes rotational acceleration now at this point we could then to all Chapter I can't rotational acceleration with Engler Motion and anger spinning and all the kinematics and all the forces that we do with linear motion a dead when I couldn't do that there really isn't time in 10 weeks to do that but part were going to do is a special case where the net short is 0 so there is no rotational acceleration of an abject is And rotational Rask not rotating and there's no network it stays not rotating And that's the best case through the book is not as Hard of the special case of no net for But to be able to do this That's showcased we do need to know that I calculate toward and that's organ a focus on today and then Wednesday and Friday will do a lot of examples of what we call a static equilibrium and that is The homework and they were dying with What will be on the next winter selected midterm will cover all the chapters on forces that you did the last 2 weeks plus this week Sowerby 3 weeks of material on the mid-term now 1 thing a lot for our This mid-term because the way of the timing throws things off just a little bit this homework assignment is due Sunday following assignments not due until Wednesday on or not Tuesday sorry Tuesday and then the quiz for this week you hopefully was due on Wednesday so the examine the timing of staff due shifted slightly from the regular what they've been which is usually Sunday and Monday so pay close attention to the due dates on the Web page you don't wanna get off luckily of anything they're moving later not Earlier so Worst-case scenario you do the homework early user doesn't get you in trouble any questions on where we're going what we're doing So again Where is it That's all of these forces That are gonna be generating the tort there will be studying and
Where does that come from a basic role as that Short 8 woes are crossed S So we introduced a new type of multiplication vector cross product again red is R cross F coming you have done the cross product before OK if you everybody again then across my razor hand array of water around some of their hand up and become their friend stuff to have lots of friends of you raise your hand vests on this right now this is Radical and 3 B so it's a good idea learn it now And 3 it with magnetic field which architecture right now it turns out it'll be actually kind of intuitive physical was 1 of places where you can usually user intuition to debt Very far and there are 3 pieces to the cross product peace wine and accumulate charts is you need to play an access The Both rotation so you end Sunday says There is an obvious 1 for you in this case mister Is the only going to rotate around here are dead In this case This is made to rotate around here but there will be some objects where You'll see you're kind of afraid of that What it rotates around You'll have to make that choice so you get to do that The next thing is we are you needed this Then thronged the axes to remove force that That is a stretch of religious placements a straight line distance of the floor saying is you need an angle between bar And the forest and this is where the cross product really comes and the across product is telling you that the angle matters And 1 way we write this As the magnitude of the cross product or about the direction and the 2nd is the magnitude of our times the magnitude of at times the size of the angle between them now what is a sign of 0 degrees There so this is all I The distance to my taxes And my bosses like danced or my is like there's some pulling on it or pushing on that Angolan 0 Or 180 depending on how you define your angles and the site 0 assigned 1 8 0 so pulling or pushing in the same direction of our makes it not rotate there's no toward an attack my equation Disney that so if you're trying to remember this sign cosine Inter Western can help you here Who is designed to get the correct answer When you push or pull long axis what is most effective way to make this thing rotate what Angola for Savannah poised The what angle Do I want to use my force to get the best rotation Monday but was a assigned Mindy want So that's maximum Much work be as at 90 degrees Any questions on that Now there's a couple other use what Use always think about it a rare demos in a moment but I wanted just drawn here so here's an all our years efforts so mangled now that I look at this and I put the 2 At the same point that's how I know what the angle theta between them is right I generally draw the forest where acting so far away is But I really want know the angle between them I need to move them like I could move actors So they're both starting at the same origin and when you do that You realize that the only part of the force The only component of the forest making anything rotate is what we call the cabana perpendicular only this Part of the force that is causing the rotation the parallel component can cause any rotation and if you look at that diagram right we see that f perpendicular it is just as signed later and so are For the magnitude of that we can writers Are at perpendicular Aloha heard make sure but just as you salt Is the idea of a perpendicular are to line of the force So we can also equivalent right as Are perpendicular times there are times were that is actually easier than picturing F perpendicular but most problems after printed Aziz Europe picture and the reason this can be very useful as I said The mail more clear As writing here is the angle between on some you're not really do That angle for some reason you might know Angolan the problem notice now as perpendicular His death throes signed them back angle But it's still at perpendicular so you can Eva His geometry Define this anger which is just 90 minus the Or you can use the fact that you need to use as perpendicular You've got multiple choice here Again that's 1 of the confusing things is really 1 idea But it's got multiple ways of doing it so you can take your favorite Or be aware of all of them any questions on this fund geometry before we now do little exercise Excellent now we need defined the direction of the torque and force them because everybody which him a right him his may sound silly comedy currently riding with your right hand That is what you're gonna do in the past Going to use the right and roll You're going to be writing you're right then will have a pending There all what that uses him is that you're right hand Now you will play Japan down your user right and a you'll do the right rule or you will get it wrong exactly so let's go over what the right him rule the ideas the following a year of my are there my Taxes that I wanted to rotation about Down in that direction which might force which way as the bargain rotate the gonna rotate Clockwise or counterclockwise clockwise if I wish Up with the force which Where it rotated counterclockwise now we have a convention in physics this is almost always positive this is negative because we have what we call it is our standard right hand coordinate system X Y and Z is out of the board the way we get this as we liner fingers of our right hand with acts and now you're hand right and pleasure Hialeahhialeah double-jointed can only grow 1 way Write it The other so you can either go like this in girl bannerlike like this incur a lot to like to wear them to point out of the border into the board variety and foreign your fingers after girl from X to Your found shows you which way is positive which way it Room got back so my look out here So 1st of all positive is direction your fun points when your fingers curled From X 2 Y now for the cross product you put your fingers along are a new parole
Torrid s so Oh let's go to a quicker questioned I'm gonna draw a particular force So organ of vivid about a here's are axes this is all are they And let's make that force F That is the short end you or Out of the board So to direct their start coming toward you were away from you mean is on this wears year done that way Jagr Etienne's Derby like a lot of this during the test the Rome fall please don't put the person next to you when you're doing the drug problem But Jagr 5 more seconds So far Three-day to white And how that most people went out of the board excellent notice what we have to do at 1 thing to do Is it helps review slide the force and pictured in your mind and your because then is Uta figure out what you're springing into My fingers R and R and young men curling and is this way You're not allowed to curl more than 180 degrees day so you get theirs and spread all around that I got does not allow The other thing you could do It is in this was a body that was the 4th which way would rotate erupted at your fingers will curled the directive that rotate from that force and then your somewhat tell you where you're into or out of the board Nablus to another 1 Of let's do that force is back your out of the boredom Alleghany India 10 seconds on this 1 but it did Endure real quick bend your out of the board The Our below Yarborough warm-up before coming to the exam to be out 5 Fall are today What excellent excellent 90 per cent of us correct we have it's covered up now Are at that Notice if I go like that as I I kept curling that and so vascular your way to do it What do y mull Suppose efforts like that Then tour out of the board Seconds 5 seconds FOR 3 Why Deutch Excellent and That is a slightly trade you 1 because notice I did accounts Force to the are there but I really draw that This looks like that as 3 is going in that direction orders in that direction so I curl that way R cross F and I come out of the board again if you think of hitting something reminded By that reminded me that rotates that way And that's what that forces Eddie questions on that so that's the Dirac said Oh yes sorry yes Exactly so But is always perpendicular to the plane the object is rotated that stylist defined in the reason being that was very useful we don't do like really do the static does obvious why you need report Europe but imagine object spinning with directed that spinning But Down years within this way But there is moving that way down here is that in this way So in Over it's been that way so in the plane but doesn't have a well-defined direction But The right general gives us want it we all agree and clockwise and counterclockwise in and out of the board well-defined now we have to agree on using a right hand to determine in and out of the board so you to make 1 decision but would you agreed on that that is well-defined so best And how Best Way To did the direction is too dry years actors a divot is plus or minus so dry Uzi axes and you either your Plaza near positives in Megan negative but have board is pretty standard and you the papers pretty standard clockwise and counterclockwise is reasonably standard Raul reading the piece of paper were looking at the lecture hall of course it's not because I stand here and it this way which way a growing I'm not going counterclockwise for you guys I believe Boeing counterclockwise for you but for me it's going clockwise because went to different sites Luckily It's very rare that I pick up piece paper and turn around greater the back so if you say clockwise counterclockwise it's pretty unambiguous war but would the same piece of paper money warning offer Where real 3 D space A mail The final piece toward Gets confusing is selecting the axis as a mad The had a rod out in space I will apply of force like that I walk at 3 distinct points a B and C & supposes rod is 5 meters long and be is right in the middle I get free completely different answers The torque whether I looked at the Talk About . 8 because remember doing at perpendicular so there be some angle theta here and at perpendicular re-signed data and are now is my 5 meters slated to 5 meters Times have signed data of I do it about me now I'm only 2 and a half meters away so much work is 2 and a half meters times signed it and finally of good about C R is what 0 and so I would get 0 and EU hits by the way are nearly meters at the 4 4 centimeters and tore doesn't yet An abbreviation But there is no meters was employed to renew energy tax energy is also a forest land the distance with It is a new and Demeter but we call it a jewel and torque and energy are very different things and so we don't actually wanted makes those units and I think that's 1 of the reasons of toward didn't get it done you know we call it nor New meter so it's clear that you're dealing with a talk with energy will call a jewel so it's clear that you're dealing with an energy but now We now see 2 way 2 dead 0 toward we can either have Equal 0 Or maybe equal 0 or 180 of course the true real wages have no force that the 3rd way but have no force I can't heavily toward noise I have 0 net force and still having net For That is possible because my forces might be a different are so the magnitude of the force might cancel but the poor might not canceled Where do you see that what we would sit right here but I would apply of course at the end of this spin
How do I know there's 0 net force on my rod when I do that The center mass doesn't accelerate anywhere right at the center of mass I told you for something uniform like this the right of the center it never goes anywhere remember when Habre when I hit my friend right when I hit my plan and it went flying up When I hear this And it doesn't go anywhere to spend 0 net But not 0 network and that's because 1 forces acting here But are equal Iraq in factors to forces there's the weight down and the forests from this object of the part Statue and then there's this force here So these 3 courses in canceled a 0 net Force upper down but this 1 R cross and is the only 1 that provides a torch This is our 8 0 0 How I So that would you got For talks Now let's look at some of these in more detail so we're having your familiar was erratic ranch Like 3 of your excellent So this is holding not right now because it's a nice ratchet wrench is earlier I could move it up but it didn't come back down unless they twist but not here Because it moves when directed a dancer got a really nice Teflon ball so there's a uniform torque applied by this With that Overcome to make it rotate and so I could use Masses to generate forces down due to their way of The here And a dozen will write if was to compute the best
The So what we have is this bar here there is of course From the center There's actually because this center has some finite size and those of course over here the there is a port Here as well that's keeping it from rotating now I applied mass down in the center here over distance have The rod and notice the torque is still canceling its not starting to accelerate this is what we would call static equilibrium Now if I hang in the past here that accelerated
But starts to to rotate and what I did Notice that injuries will force any right of course is still the same saying Mass ideas are bigger right
So if I come over a year And I have now of course over just this force I'm now using Al some comparing the Torquay equal to Ella times FW versus the Being held climbs FW and of course T 2 is bigger than T Y and it starts to ban Now this is a case where the idea
But Perpendicular It makes a lot more sense the force Perpendicular because the forces always straight down considerably from weight and now but put up high enough Do you see it doesn't slide down right now that torque is not great enough because I'm an angle You can even think of it as this component of the forest is the only component of rotate or forces now acting over a shorter distance right actor perpendicular distance not before we call this the lever arm as a leverage that you're dead is married to make this work OK so let's go ahead and draw that in our picture
Right so that was playing the Mehsud different places but I can also B up at an angle hang my forced down and now this is effective are perpendicular and my tour about that point is are perpendicular Times at and this is less than the magnitude of art Now of course if I make the 1st beggar It will down so whether that I locked it in place It was literally just that I had a bigger angle eliminate the angle even bigger But The masses will support it Oh I guess not show good thing I moved Our but that 1 is an hour we destroy military duets Let's make it really definite So now I really really short Lever arm faces this long enough And I'll stay up there That's what now but of course
I can do is I can going close and ask forget how many masses support for again is my real a short level on shorter distance and told into Don't At solving 380 And it's supposed to well Turn with 4 Barely not It well turn with 4 members of the project so But there is a combination All 3 Book Total cost exactly where the forces acting the angle between the 4th and not need all 3 of them so This
That is really a great visual for that Any questions on that aspect of it The us So we don't actually Notice the rule is the following it this is our The angle between half an hour is always the angle you get from going less than 180 sees his way to do it because I'm here Right that's rotating it this way If I'm here Which is the negative fade That's rotated the other way I notice that minus sign that gives you the correct answer in your RF signed data right is assigned a negative data is negative the sign a positive data so you will get correctly that its negative now for most calculators but this is the Sabres with renewable most calculators these days but never used to be that smart but I put that angle also get the negative End the show so you do wanna be careful when plugging you're angle values into your calculator you correctly getting the positive and negative and that's why I always recommend checking signed a START 8 SIGN bite Using your right hand rule and not just relying on your calculator for that date because at IRS signed it is really the magnitude of the tort that the safest way to do it now before you decide plus lover laced up 2 minutes Where we going that everything we're going to be doing now for the next 2 days is about a special case of static Equilibrium static Means not moving so velocity 0 equilibrium means not changing so 8 0 0 hours We can't have not equal to 0 and 8 0 that would just be equilibrium Oregon be doing static equilibrium and at the same time no rotation or rotational acceleration Everything's gonna be about Senator Beagle 2 0 on the net and the net For equal to 0 and that's why we needed to be able a calculate for Baffert context which were going to use it soared as did today the examples
Analyzes review friction tents and all of that