I will continue to add captions. All should be added by 10:00PM, 9/23/18.
PhyFl18SS1.6.1 The resultant vector needs to be in a different color. A proper description of a vector requires magnitude, units,angle, quadrant.
PhyFl18SS1.6.2 All angles are measured from the horizontal (with some exceptions) If it is a map view, this is how you describe the quadrant that you are in.
PhyFl18SS1.6.3 A displacement vector (or any vector for that matter always starts at the begining and is a straight arrow to the end. The path that the object takes does not matter. ∆s in blue is a displacement vector. It only cares about the beginning position and the final position. The displacement vector of my life would start in Ponca City Hospital and probably end where I am teaching at NHS. It doesn’t care where I have visited and lived in my life. It only cares about where I was born and where I died. It would be a 124 milelong straight displacement vector.
PhyFl18SS1.6.4 A vector at an angle is the hypotenuse of a right triangle. So if you are going at 4 yds/sec at 45° N of E, you represent that with an arrow that has a length of 4 yds/sec (at whatever scale you assigned that velocity vector), but you are also going 2.8yds/sec east and 2.8 yards per second north. You are actually going all three velocities at once. Weird, huh? Either we do it this way with 2D motion or you learn how to plot everything in 3D (∆x,∆y, and ∆t).
PhyFl18SS1.6.5 We went out to the courtyard and did a couple of pinwheels. From this exercise, you should start to get a feel of circular world vs. linear world. We all went the same omega (angular velocity), but we went different 2D linear velocities.
PhyFl18SS1.6.6 Still on the courtyard pinwheels. If we say it took us 10 seconds, then we had an angular velocity of 2π/4 radians per 10 seconds (=π/20 radians per second)
PhyFl18SS1.6.7 So far we have talked about displacement and velocity being vectors (magnitude and direction) and time is a scalar (no direction). What about baby omega? Is it a vector or a scalar?
PhyFl18SS1.6.8 It turns out that omega (angular velocity) IS a vector. But what about it’s direction. Since the object is rotating (or at least going in circles) how do you represent this circular motion with a straight arrow? You gotta go third dimension bro. So you represent the omega with an arrow coming out of the page for counter clockwise rotation (CCW). You represent an arrow coming out of the page with a dot and a circle around it (sometimes just a dot)
PhyFl18SS1.6.9 You represent clockwise rotation (CW) with an arrow going INTO the page. An arrow into the page looks like the arrows tail feathers left an impression on the page (like an “x”). The arrow is along the axis of rotation.
PhyFl18SS1.6.10 Circular world vs. linear world. For wevery relationship (think equation) in linear world, there is a corresponding equation in circular world.
PhyFl18SS1.6.11 Definition of a radian. The question came up . . . “Why don’t radians have any units?” Because they are a ratio of the arc length of a circle (∆s) and the radius of that d
PhyFl18SS1.6.12 From the three base equations (on the left) we derived a very useful, very important equation in Physics which bridges linear world to circular world. You will have to know this derivation for TEST 1B. .
PhyFl18SS1.6.13 Here’s the good old what is the omega of the second, minute, and hour hand which you will find in every Physics textbook.
PhyFl18SS1.6.14 converting radians per second to rpm (revolutions per minute) Like what your tachometer measures on the dashboard of your car.
PhyFl18SS1.6.15 From that bridge equation we derived, here is another useful minibridge equation relating linear velocity to angular velocity.
PhyFl18SS1.6.16 I spun the wheelchair tire in front of the classroom and you timed it. We got 5.7 radians/sec. when multiplied by the radius of the tire we see that the outside of the tire is rotating at 1.6m/s
PhyFl18SS1.6.17 The period (Tp) is the time it takes an object to complete one revolution. Like the period of the earth is 24 hours or the period of the earth around the sun is 365 days. Period can also mean the time it takes a pendulum to come back to its original position. Period is the inverse of frequency.
PhyFl18SS1.6.18 Here we were looking at the period of the spinning wheel in front of the class.
PhyFl18SS1.6.19 Period talk.
PhyFl18SS1.6.20 The wheel spinning up front. Using the brige equation to determine its velocity.
PhyFl18SS1.6.21 Here we are trying to figure out how many miles per hour the spinning wheel would be going it it were attached to a bicycle.
PhyFl18SS1.6.22 The point I was trying to make with this discussion was that the moon is moving at 2300mph, but appears to us to be moving hardly at all. The reason for this is the very long radius. Since omega = v/r. Since r is soooo big, it wipes out the huge v. the omega is what we perceive as we stand below an object rotating above our head. A jet may be going at 600mph, but because its radius (from us) is, say, 50,000 ft, it doesn’t have a very big omega so it doesn’t seem like it is going that fast to us. There are probably those out there who would call its speed of 600mph “fake news” because they themselves do not understand circular motion kinematics.
PhyFl18SS1.6.23 so when the radius is large compared to the velocity, the object appears to be going slow to us down below. This sounds like a good essay question for Test 1B.
PhyFl18SS1.6.26 If you see “SH” on your test from ym grading it means you should have used a ruler. It stands for “shaky hands”
PhyFl18SS1.6.27 If you see this on your test from my grading it means that I followed your mistake so you missed less than you would have if I was a computer and was grading your test.
PhyFl18SS1.6.28 It is much better the search the Facebook group for what your are looking for than the scroll scroll scroll.
PhyFl18SS1.5.2 Here is a unit analysis you all did on the board. It turns out it takes light 1.28 seconds to reflect off the moon and hit the earth.
PhyFl18SS1.5.3 I paid off 1st hour 3 dozen donuts to keep me out of the limelight. I was worth it.
PhyFl18SS1.5.4 Here is the sample problem from 1.6
PhyFl18SS1.5.5 Newton’s is a suitcase. Meaning that it is combo unit that contains smaller units. Many times, you have to open these suitcases when you are doing unit analysis. Other examples of suitcases are Joules (kg.m.m / s. s) and Watts (kg . m . m / s . s. s) but we’ll worry about those later this year.
PhyFl18SS1.5.6 You can’t have double decker fractional units in Unit Analysis. units can be multiplied inside a cell, but they can’t divided inside a cell. I will explain this better in class.
PhyFl18SS1.5.7 Free Body Diagrams (FBDs) are used to show all the force vectors acting on an object. Here was the example we did in class of a car driving down a horizontal highway at a constant speed of 60mph.
PhyFl18SS1.5.8 On 1.6.3 the object was a volleyball moving through the air. So in that case there are only two main forces acting on the ball. The force of gravity and the air drag (Ra)
PhyFl18SS1.5.9 Here is most of the GSUA for 1.6.3 I ran out of room here, but you can see the whole thing on the Key to 1.6 on the Facebook Group.
PhyFl18SS1.5.10 In general here is what GSUA looks like. You do your labeled drawing, determine the correct equation and isolate the desired variable in the top row, then you are ready to lay out your givens (just as they are written in the problem. After you do that, you draw the squiggly line, then all that is left to do is multiply by a bunch of conversions which are really just clever forms of 1.
PhyFl18SS1.5.11 The famous pesky fly problem.
PhyFl18SS1.5.12 heres how one student solved it
PhyFl18SS1.5.1 Here is a clever solution involving a graph. I actually used this method to quickly solve the problem on the THT1A.
PhyFl18SS1.5.1 Another students work in solving the Pesky Fly. (1.7.2)
PhyFl18SS1.5.1 Here is the complicated drawing from 1.7.3 I just noticed that I never took a pic of the position vs. time graphs on the other board, but that is okay, because I have the key posted on the Facebook Group.
PhyFl18SS1.5.1 Remember, in better way to write, you are trying to substitute the given unit for a unit that will eliminate as much of the scientific notation as possible. It’s why I don’t say that it is 442,000 inches to the Warren Theater. That is true, but there is a Better Unit to use (miles in this case)
PhyFl18SS1.5.13 BWTW example
PhyFl18SS1.5.14 BWTW example
PhyFl18SS1.5.15 Sam Nobel Museum where the Astronomy talks are held.
PhyFl18SS1.5.16 This actually doubled the record of students voluntarily attending an Astronomy lecture.
PhyFl18SS1.5.17 even more students!
PhyFl18SS1.5.18 my sloppy notes from the talk on Galaxy formation
PhyFl18SS1.5.19 Well, there are at least 3 out of 4 Alberts at the Astronomy Talk.
PhyFl18SS1.5.20 Circular motion will end up being Black Kinematics
PhyFl18SS1.5.21 Pi is the ratio of the circumference of a circle to the diameter of the circle
PhyFl18SS1.5.22 Doesn’t matter how big the circle is, The ratio is ALWAYS pi (3.14 . . )
PhyFl18SS1.5.23 Us doing a pinwheel out in the hallway.
PhyFl18SS1.5.24 We started talking about baby omega.
PhyFl18SS1.5.25 We ended up doing a quick UA getting radians per secon into Revolutions per minute (rpm).
This is from Wed,Thurs,Fri. Remember, you can print out any of these screenshots and captions and tape them into your notebook when ever you want as long as it is done before Packet 1 Notebook check on October 2nd.
PhyFl18ss1.2.1 We started off Wednesday’s discussion trying to sit as still as possible. No matter how we tried, we couldn’t really be motionless because the room was moving, Oklahoma was moving! In order to be motionless we would have to stop the world from spinning on its axis. Knowing the circumference at the equator (approx 3900 miles) we can figure out how fast we are moving. The circumference of the Earth is approx 24,000 miles (to 2 siggies). So since it takes us 24 hours to go around once, we are moving at 1000 miles/hour at the equator. But what about Oklahoma? We don’t have as far to go. Connor did some work and figured out that we are moving at 850mph just sitting in your chair. So if I could stop the orld spinning on its axis, would that make you motionless?
PhyFl18ss1.2.2: No! Because the earth is orbiting the sun. So how fast is that? On average, the earth is 92,000,000 miles away from the sun. So let’s do the same thing we did with how fast we are moving on a spinning earth: See the Unit Analysis above (we’ll practice that method A LOT as the year goes on). When we run the numbers we find that the earth is blazing through the vacuum of space at 66,000 miles per hour!! WOW! That’s cray cray. So . . . if I can stop the earth moving through space, can I finally say that you are motionless sitting in your chair?
PhyFl18ss1.2.3 In 1718, Isaac Newton realized that that there was all this motion going on (earth spinning and orbiting) and he felt like there had to be an ultimate reference point. The earth and the other planets had to be sitting in something, right? There had to be a nonmoving medium for those light waves from the sun to travel through. (For example, sound waves need a medium (air, water, or solid) to travel through). So Newton logically concluded that there had to be this fabric of space that allowed light to travel and that fabric he called “The Luminous Aether” Since Newton was a true stable genius pretty much everyone agreed that this sounded pretty damn smart and the Aether (we spell it ether today) was there eventhough we couldn’t see it, feel it, or smell it. Finally, in 1887 Michaelson and Morely actually used a series of very expensive experiments involving an interferometer at Case Western University in Cleveland, Ohio. To find evidence of the Ether Wind. No matter how precise their instruments, they couldn’t find any evidence of the Eather Wind. We finally had to conclude that there IS NO ETHER. The Earth , Sun and Planets are just floating in . . . . in . . . pure nothingness. Today we know that there is really no such thing as nothingness, but that is a whole different discussion.
PhyFl18ss1.2.4 So even Galileo and Newton assumed that the sun was not moving. Well . . . turns out it moves at around 500,000 mile per hour on its journey around the Super Massive Black Hole at the center of the Milky Way Galaxy. A Galactic Year is how long it takes the sun to go around once. Since our solar system is around 4,500,000,000 years old that means we are somewhere in the neighborhood of 18 galactic years old. Still teenagers! When we were 17, there were dinosaurs walking around the Earth.
PhyFl18ss1.2.5: So if I could stop our solar system would that finally make us motionless? NOPE! Locally, the Milky Way is on a crash course with much bigger The Andromeda Galaxy. But . . . didn’t Edwin Hubble figure out that all Galaxies are spreading apart? True, but there are local exceptions to this general rule. One POSSIBLE explanation is that there is a clump of Dark Matter between the Milky Way and Andromeda that is attracting us together. We are coming together at a speed of 250,000 miles per hour. Yikes! See the Facebook group for the animation show coming attraction over the next 8 Billion years.
PhyFl18ss1.2.6 Fritz Zwicky proposed this idea of Dark Matter in 1933 (he was laughed at and mostly ignored). I wish he had called it the Dark Attractor, because it isn’t matter like we think about. Neil De Grass Tyson proposes calling Dark Gravity, but I don’t like that either because it doesn’t follow the rules of gravity. There is also Dark Energy out there (or right here in this room). It spends all its time trying to rip you limb from limb, it wants to rip your molecules apart, it want separate your atoms, it would love to separate the quarks that make up your protons. Dark Energy is a bad descriptor, because this doesn’t act like that energy you learned about in Chemistry (remember Joules?) I propose that we call Dark Energy The Dark Separator. People fear or love Slender Man. I guess the Dark Separator is the Slender Man of the Universe. No one’s relly seen it but we know he is there. Out there somewhere . . . waiting. If The Dark Separator wins the Universe will end in a “heat death”.
PhyFl18ss1.2.7 So if you could stop the Milky Way from moving, then you still have the problem that spacetime itself is expanding (daggone it Einstein and Hubble!) So we have to settle with this definition of motionless.
PhyFl18ss1.2.8 Back to the basics. Here is the graph of out four “journeys” on the West Lawn. And the corresponding 4 equations.
PhyFl18ss1.2.9: OUR FIRST EQUATION!! We call this the Red Equation.
PhyFl18ss1.2.10 These are the four Equations from the graph on Sheet 1.3. We left the numbers with 2 siggies.
PhyFl18ss1.2.11: So I guess we ought to talk about scalars and vectors. x, y, and z are just position points. They have no direction. All changes (capital delta (∆)) in position involve MOVING from point A to point B so they are called VECTORS.
PhyFl18ss1.2.12 Scalar vs. Vector
PhyFl18ss1.2.13: Delta (∆) represents change. So what if the change is very tiny. No, I mean VERY tiny. As the delta triangle gets smaller and smaller and smaller it eventually gets so smaller it becomes infinitely small at that point we call the change “lil d”
PhyFl18ss1.2.14 “lil d” means instantaneous change in position, in velocity, in acceleration, in temperature, in jerk, in time, in whatever you want.
PhyFl18ss1.2.15 Who was the first one to think of “lil d”? Actually two people in the 1700’s. Isaac Newton (English Genius) and Gottfried Wilhelm (von) Leibniz (German Genius).
PhyFl18ss1.2.16 This is from Sheet 1.3 The 4th function you were supposed to come up with the equation for. Remember, to find the slope, it is just the “rise” (which is negative ∆x in this case) over the”run (which is positive ∆t)
We’ve been doing a lot of introductory stuff, but we finally got going late in the hour on Monday. We went out to the West Lawn and uniformly walked from the sidewalk by the science lot to the sidewalk by Main Street (50 meters). We timed ourselves doing it. Then we uniformly jogged from the sidewalk by Main street to the sidewalk by the science lot. That was about it for Monday. We came back in, I handed out sheet 1.2 and we wrote down our times. The following Screenshots are from Tuesday (8/21/18) The discussions went many different ways in the five classes, but here is what each of the discussions had in common. In other words, here’s the part you are responsible for so far:
This is just a brief introduction to sig figs. We also call them siggies, significant figures, significant digits and just plain sigs.
The more significant figures there are, the more accurate your number, but the accuracy comes at a price.
Fractions can’t be used for measured numbers (or the manipulation of measured numbers). The reason is that you can’t show sig figs with fractions. For instance 22/7 is the fraction for pi which has an infinite number of digits. Obviously, no instrument is that accurate, so you have to “round and truncate” pi to show the proper number of sig figs. We’ll talk about sig figs more later. This is good enough for this first introduction.
Here is our plot of the first walk from the science lot sidewalk to the main Street sidewalk. It also includes our first Physics equation. THis happens to be from 3rd hour.
This is from 6th hour’s discussion. Notice the 2nd line is from the run BACK from Main Street (negative slope).
Here are the pics and screenshots with captions from last week:
PhySP18SS6.7.1: Add your pics to the wall!
PhySP18SS6.7.2: Ultimate fighting Tool used to solve a free fall problem. The mark of a great question is that it reduced down to other lesser equations (like the 3rd Blue)
PhySP18SS6.7.4: 6.15.12 Using UFT to solve a problem
PhySP18SS6.7.5: A very famous graph in Physics. E = K + U which means Total Mechanical Energy = Kinetic Energy plus Potential Energy. And . . . the Total Mechanical Energy (E) is conserved which means you can’t lose any or gain any in a closed system.
PhySP18SS6.7.6: The difference between dot products and cross products. Pretty much everything you do all day is a series of dot products and cross products. Anything involving changing energy is a dot product of two vectors and anytime there is any rotation it is a crossproduct. Heck, if there is light anywhere around you it is the combination of two dot products and two cross products.
PhySP18SS6.7.7: THe Natural Balance Point is pretty much what it sounds like it is. It is the point that gravity recognizes. As far as gravity is concerned ALL the mass of the object is at the NBP. The NBP has an equal mass distribution radially (called the moment of Inertia (I).
PhySP18SS6.7.8: Torque is the only type of cross product we use, but there are many more.
PhySP18SS6.7.9: 3D torque. Sometimes I forget how awesome torque is.
PhySP18SS6.7.10: Messing around with torque in general. This doesn’t go to a particular problem. We jsut made this one up. It is a static problem so it can’t move in any direction OR rotate.
PhySP18SS6.7.11: We made this one up too.
PhySP18SS6.7.12: yep, made it up
PhySP18SS6.7.13: This is from Sheet 6.16.1 Only 1st hour did this one.
PhySP18SS6.7.17: THT6B.12 the second one with Levi and Daniel and all that crazy organic manure.
PhySP18SS6.7.18: 6.16.5 which also helps you with THT6B.15
PhySP18SS6.7.21: THT6B.14 It’s fine if you just want to think of phi as the reference angle, but just so you know it is actually the obtuse angle that extends from the LOA all the way around to radial pointer vector. This has to be the case because Torque has to be negative for this situation since it is causing clockwise motion. All clockwise rotation is negative. So . . . since torque = |r| |F| sin (phi) phi must be in the 3rd or fourth quadrant for sin (phi) to be negative. If that didn’t make sense, don’t worry, it’s too late in the year to worry about it.
PhySP18SS6.7.24: The fishing pole one. 6.16.7
PhySP18SS6.7.25: The Matrix version of the cross product solution. This looks hard, but turns out to be laughably easy..
PhySP18SS6.7.26: 6.16.10 This is the reason WHY it becomes so easy. As long as you can get a column of your 3 x 3 matrix a column of zeros, your life is easy. This will be the case for your test next week.
PhySP18SS6.7.27: more torque stuff
PhySP18SS6.7.28: more torque stuff
PhySP18SS6.7.29: more torque stuff
PhySP18SS6.7.30: We used to have a torque building contest where you had to have to make a mobile which has at least four different torque and hang it from the ceiling. What happened to all those?