PhySP18SS6.6.1: 1st hour after Horsepower Man/Woman

PhySP18SS6.6.2: 2nd hour

PhySP18SS6.6.3: 3rd hour

PhySP18SS6.6.4: 6th hour

PhySP18SS6.6.7: 7th hour

PhySP18SS6.6.5: Some of the top results

PhySP18SS6.6.6: Yemi was 2018 HorsePower Man (2.14 hp)

PhySP18SS6.6.8: Guin was the 2018 HorsePower Woman. I made her take the photo when she was trying to eat breakfast.

PhySP18SS6.6.9: On running stadium steps: We were only concerned with the work it took to beat gravity. We only took into consideration the ∆y. We assumed the ∆x work was negligible.

PhySP18SS6.6.12: From sheet 6.13: This was the bit on stack and mult. When you are dotting a force vector with a displacement vector and they are given in terms of I roooooof and J rooooof, all you have to do is stack them and multiply the i component of the froce by the i component of the displacement. that value will NOT have a direction since i dot i = 1 since i dot i = (1)(1)(cos0). The same holds true for j dot j. Therefore the direction gets dotted away and you end up with a scalar (the i components multiplied together added to the j components multiplied together.

PhySP18SS6.6.13: Another example

PhySP18SS6.6.14: From 6:13. Another way of looking at Work. The graphical way. As long as there is multiplication in the suitcase, there will be a graphical way of looking at the concept. When I say graphical think Calculus. Graphical solutions in this class turn into integral calculus solutions in the Physics classes that come later. Integrals are AWESOME! Such beauty. Such poetry in the Cosmos. The language of “God” my friend.

PhySP18SS6.6.15: Pretty simple, area = work done by the force through the distance.

PhySP18SS6.6.16: I added this repeat because I wanted you to see the big Thermodynamics picture. When the force does the work on this system 220 Joules worth of energy flow into the system. Remember doing work (positive or negative) on a system changes its Joules of energy.

PhySP18SS6.6.17: In this case we started off adding Mechanical energy to the system for the first 7 meters, then the outside force (s) started draining energy from the system. So you added 28Joules worth of energy, but drained out 110Joules. Therefore, you KNOW the system had to have kinetic energy (it must have been moving) to begin with. I say mechanical energy since we are in a Mechanics class. I suppose it could start off as gravitational energy (energy of position) or chemical energy (tied up in chemical bonds) or nuclear energy (tied up in nucleons), but there HAD to bo some kind of Potential or kinetic energy to begin with. You can’t take $110 out of a bank account that only has $28 in it. Or . . . you can’t pour 110 gallons of water out a tank that only has 28 gallons of water in it.

PhySP18SS6.6.18: More example of area and integral notation.

PhySP18SS6.6.19: . . .

PhySP18SS6.6.20: . . .

PhySP18SS6.6.21: . . .

PhySP18SS6.6.22: This is the book that Apollo 13 was based on. It was written by Jim Lovell (played by Tom Hanks in the movie). If we don’t get a chance to finish it, you should catch it on Netflix.

PhySP18SS6.6.23: Derivation of the Work – Kinetic Energy Theorem. This is the boring algebra version. The calculus version which you will learn next year in AP Physics is beautiful.

PhySP18SS6.6.24: The simplest kind of potential energy: Gravitational Potential. It is called energy of position because it depends on the weight of the object and how high above the “zpl” the object is.

PhySP18SS6.6.25: Problem 6.15.6 You need to stop using F = ma and start using W-K Theorem to solve Physics problems.

PhySP18SS6.6.26: 6.15.7 Same idea as last problem only this one is on an inclined plane.

PhySP18SS6.6.27: repeated because this one has #s.

PhySP18SS6.6.29: 6.15.8 (at least what leads up to it). This is from the demo we did in the hallway.

PhySP18SS6.6.30: Data from the hallway demo.

PhySP18SS6.6.31: More demo data

PhySP18SS6.6.32: We noticed that when you double the speed of the lego block, it takes the friction from the block floor contact 4 times as long to stop it!

PhySP18SS6.6.33: This data gave us a 2.5% error which is amazing even for college when you are dealing with the entropy of friction.

PhySP18SS6.6.34: So applying this idea to cars. That you Emilie du Chatelier. 120 years before her time. Stupid Newton.

PhySP18SS6.6.35: The big pendulum in the room introduces us to the UFT (Ultimate Fighting Machine)

PhySP18SS6.6.36: If you plot the x only position of the bob on a pendulum you will get a cosine wave. Notice I said cosine, not sine.

PhySP18SS6.6.37: Stable vs. Unstable Equilibrium. This is a big Thermodynamics concept. If you perturb a stable systems equilibrium it will naturally tend to go back to its ground state equilibrium. If you disturb a system in an Unstable Equilibrium it will ACCELERATE AWAY from it’s equilibrium position. If you disturb an system in Neutral Equilibrium it will neither go back to its original Equilibrium or accelerate away from its original equilibrium. It will just establish a new equilibrium. I guess you can catagorize people like this. I think I am a neutral Equilibrium guy. I change my way of looking at the world all the time, but I guess I am just about as cool with the new perspective as I was with my old one.

PhySP18SS6.6.38: The baby UFT. Learning this starts you on a journey that you will be on until either you have triumph or you go the way of Einstein, Heisenburg, Feynmann, and Hawking. It will haunt you until your deathbed last attempt to solve it. What a glorious life you will lead!

PhySP18SS6.6.39: The absolute basics of energy. Since the overall total mechanical energy is constant (E), whatever Joules you take away from kinetic energy, you must add to Potential Energy and vice-a-versa. See how simple the universe is?

PhySP18SS6.6.40: UFT in all its glory. Don’t worry, you won’t be expected to start using it until March of next year in AP Physics. It will become your lifeline in there.

PhySP18SS6.6.41: We did a thing on Edison vs. Tesla because of 6.15.9

PhySP18SS6.6.42: Edison was all about DC current which means these electrons are all moving in one direction.

PhySP18SS6.6.43: DC current is the kind of electricity that comes from the REDOX (Oxidation/Reduction) chemical reaction that takes place in your battery. It provides the push of copper’s valence elctrons through the circuit.

PhySP18SS6.6.44: DC (Edison) vs. AC (Tesla)

PhySP18SS6.6.45: The generation of Alternating Current (AC). Rotating a coil of wire in a Magnetic filed causes the electrons to move back and forth. That is ALL you need for electricity. Moving electrons . . . doesn’t matter what direction they go.

PhySP18SS6.6.46: So in this case (we did an animation in the presentation) the electrons are moving back and forth.

PhySP18SS6.6.48: We generated our own AC current in class.

PhySP18SS6.6.49: More details on how AC current is formed. This will be what you will become and expert at in E&M.

PhySP18SS6.6.51: The inner working of Tesla’s generator

PhySP18SS6.6.47: Where Tesla really excelled is his polyphase AC current. It was as reliable and steady as Edison’s DC current.

PhySP18SS6.6.52: Tesla broke with Edison and Westinghouse became his money man.

PhySP18SS6.6.53: Westinghouse and Tesla did some “back of the envelope” calculations at the base of Niagra falls and realized they could make a fortune

PhySP18SS6.6.54: 6.15.9 Here’s the math they did. And we get a new equation for Power out of it.

PhySP18SS6.6.55: How hydroelectric power is generated.

PhySP18SS6.6.56: You have to have a way to turn the coil of wire.

PhySP18SS6.6.57: THe gravitational potential energy behind the Niagra Falls plant.

PhySP18SS6.6.58: Hydroelectric power in a nutshell

PhySP18SS6.6.59: Worlds first

PhySP18SS6.6.60 Tesla’s Polyphase patent

PhySP18SS6.6.61: . . .

PhySP18SS6.6.62: Buffalo, New York became the world’s first city of electric light. NYC got jealous real fast

PhySP18SS6.6.63: Buffalo!!

PhySP18SS6.6.64: Westinghouse screwed over Tesla just like JP Morgan did. John Astor was coming the America to rescue Tesla financially.

PhySP18SS6.6.65: Unfortunately Astor was the number one passenger on JP Morgan’s Whitestar Line’s flagship Titanic.

PhySP18SS6.6.66: The controvery of the time was: Did JP Morgan set up Astor to die on the Titanic?

PhySP18SS6.6.67: Tesla was basically destroyed when Astor drowned.

AP Test Week #1 so we had to move a little slower.

PhySP18SS6.5.1: It took Tatum awhile. The icing looks like a nebula.

PhySP18SS6.5.2: F&F6.1

PhySP18SS6.5.3: F&F6.1

PhySP18SS6.5.4: F&F6.3

PhySP18SS6.5.5: F&F6.6

PhySP18SS6.5.6: We talked about the reversing of the Earth’s Magnetic Field

PhySP18SS6.5.7: We REALLY need our magnetic field to protect us from the Solar Wind.

PhySP18SS6.5.8: The problem is, what happens while the field flips?

PhySP18SS6.5.9: The way it is going to be (in your lifetime)

PhySP18SS6.5.10: “Work” leads to changes in Kinetic Energy.

PhySP18SS6.5.11 Work-Kinetic Energy Equation

PhySP18SS6.5.12 Dot products in general give you a number which represents how much the two vector arrow directions agree with each other.

PhySP18SS6.5.13: So work is a dot product between Force vector and displacement vector. The number tells you how much the kinetic energy of your system will increase or decrease.

PhySP18SS6.5.14: . . .

PhySP18SS6.5.15: Another big suitcase.

PhySP18SS6.5.18

PhySP18SS6.5.19

PhySP18SS6.5.21 Let the cosine ONLY tell you whether the force does positive work or negative work over the displacement. If the angle bewtten the Froce vector and the Displacement vector is in the 1st or 4th quadrant that force will do positive work and will increase the kinetic energy of the system. It the angle between force and displacement is in the 2nd or 3rd quadrant then the force will do negative work on the system and the system will lose kinetic energy and therefore slow down.

PhySP18SS6.5.22 That top equation is a good one to use for many different situations.

PhySP18SS6.5.23 I found this girl and her boyfriend hanging out on campus. I asked her if I could take her picture balancing on the tightrope. So, why do you think she holds her arms out to help her balance. (Hint: It has to do with moment of inertia (her mass distribution from her potential axis of rotation)

PhySP18SS6.5.24 The work the normal force from the chair does on me as I stand up on the chair at a constant rate. Overall there was NO work done on the system. The normal Force did positive work, but while I am rising with no acceleration, there was no overall work being done. The normal force does positive work and gravity (mg) does negative work. ∑W = 0 Nm.

PhySP18SS6.5.25 Dropping a tennis ball, gravity (mg) does positive work since cosine =0 and it speeds up the ball. Gravoty ios pouring energy into the system.

PhySP18SS6.5.26 Pulling the cart. No work by gravity (mg) because it is 90° to the displacement vector (∆x). THe force of pull does positive work (cosine 0 = 1) and the friction does negative work (cosine 180° = (-1)).

PhySP18SS6.5.27 Doesn’t matter which direction you push on the wall. As long as it doesn’t move, the work done by the push will be zero.

PhySP18SS6.5.28

PhySP18SS6.5.29

PhySP18SS6.5.30

PhySP18SS6.5.31

PhySP18SS6.5.32 Work done by the participating forces for an object being pulled at an angle up a hill) Notice gravity force (mg) is at an obtuse 2nd quadrant angle so cosine = (-1)

PhySP18SS6.5.33: An object moving DOWN an incline at a constant velocity.

PhySP18SS6.5.35 Sliding into base. The only force doing work is the force of sliding friction (fk)

PhySP18SS6.5.36 Flight attendant pulling on his/her flight bag.

PhySP18SS6.5.37

PhySP18SS6.5.38

PhySP18SS6.5.39 From Friday: Dot products of unit vectors.

PhySP18SS6.5.40 When dotting two vectors given in i j format it is real easy since F O I L turns into F L.

PhySP18SS6.5.41 Example of “Stack and Mult”

PhySP18SS6.5.42 The force acts THROUGH a distance in a dot product. So the work is a measure of how much energy the force added to or took away from the system. Stack & Mult is a really easy way to determining whether energy is flowing into a system or pouring out.

PhySP18SS6.5.43 . . .

PhySP18SS6.5.44 . . .

PhySP18SS6.5.45 . . .

PhySP18SS6.5.46 We’ll discuss more Monday

PhySP18SS6.5.47 We’ll discuss more Monday

PhySP18SS6.5.48 got some good candidates in the contest.

PhySP18SS6.5.49 We’ll discuss when we run stadium steps.

We really only had two days this week to go over new material since Wed – Fri was testing stuff.

PhySP18SS6.4.1 Clever Barrista

PhySP18SS6.4.2 Salvador!

PhySP18SS6.4.3 My favorite painting of Dali’s. This is a MASSIVE painting at the museum. It takes up the whole of a very tall wall. I stood and stared at it for an hour until Jamie pulled me away. She said something about helping her with the boys.

PhySP18SS6.4.5 With pulley systems we must melt the x axis around the pulley. Thanks Salvador!

PhySP18SS6.4.6 5 rules of pulleyland.

PhySP18SS6.4.7 You most simple, basic pulley problem.

PhySP18SS6.4.8 Simple Pulleys are just another way to change the direction of the effort force you must out in to lift an object or let an object fall gently to the earth. You know how inclined planes “dilute” gravity? Well, so do pulleys. They dilute gravity. Notice how this one cuts gravity by 75%.

PhySP18SS6.4.9 Here is a twist on the simple pulley problem. Now it is just the inertia (not the weight) of one of the boxes that is diluting gravity. In this case it is also the friction, but sometimes the surface is frictionless and it is JUST the inertial mass that is diluting gravity. Physics teachers love this problem because it gets at one of their favorite subjects — separating out gravitational mass and inertial mass).

PhySP18SS6.4.10 Ah . . . full blown Inclined Plane/Pulley Problem. We use the villatoro Short Cut for this kind of problem.

PhySP18SS6.4.11 Joel Villatoro was always trying to find shortcuts to working Physics problem.s. This one stuck.

PhySP18SS6.4.12 . . .

PhySP18SS6.4.13 . . .

PhySP18SS6.4.14 . . .

PhySP18SS6.4.15 Fastest way to solve it is with the VSC.

PhySP18SS6.4.16 THis is about as hard as the Inclined Plane-Pulley problems will get this year.

PhySP18SS6.3.1 Truss static problems are notoriously mean and nasty in Physics. Here is a short cut that comes in handy for “y shaped” connections.

PhySP18SS6.3.2 You can turn the force vectors into a scalene triangle using a little “parallel lines cut by a transversal” geometry to help you determine the angles. Once you have the angles and one force vector, you can determine what the other two forces are by employing the “Law of Sines”.

PhySP18SS6.3.3 Here is an extreme case of a y shaped truss problem. The tensions in the cables go to infinity as the angle gets really small.

PhySP18SS6.3.4 Inclined planes. You must tilt your axis to save you a lot of pain. Typical strategy for solving these: carefully draw FBD (tile axis), then ∑F= max, then one of the orange kinematic equations.

PhySP18SS6.3.5 Elevators are a favorite of Physicists because they go from Inertial Frames of Reference to noninertial frames of reference if you push the up the up or down button. By doing that you cause the system you are standing in to accelerate. When the system you are engaged in accelerates and you don’t know it’s accelerating, it is considered a non inertial frame of reference. Normal physics won’t work for you. For instance, when you hit the up button in an elevator you feel like you just gained 20 lbs (magic?, no just acceleration)

PhySP18SS6.3.6 Same thing as previous screen shot shown a slightly different way.

PhySP18SS6.3.7 Some numbers in the elevator equation.

PhySP18SS6.3.8 What is the cable breaks. Einstein had one of his happiest thoughts when he went through this thought experiment.

PhySP18SS6.3.9 The old alien trick. They can fool you that you are back on earth if they hook up a cable to your floating elevator in interstellar space and start dragging your frame of reference with an acceleration of 9.81m/s/s. You will think you are back on earth, open the door and . . . be introduced to the vacuum of space. sucka!

PhySP18SS6.3.10 Here is another example of a noninertial frame of reference. If the train car is accelerating Unbeknownst to you, you will think there is a ghost in there with you because that ball hanging from the ceiling will mysteriously hang at an angle.

PhySP18SS6.3.11 So Einstein said . . . Is it gravity or acceleration? THey are essential equivalent. This is one of the main principles of General Relativity

PhySP18SS6.3.12 Is she on earth or just accelerating in space.

PhySP18SS6.3.13 Did that ball drop because he is on Earth or because he is accelerating upward?

PhySP18SS6.3.14 . . .

PhySP18SS6.3.15 This also sort of makes you think about the bending of light. Turns out . . . it DOESN’T really bend. Either the space-time continuum is curves and light is just following the most “horizontal” path available or the reference frame is accelerating upward so light APPEARS to bend. So Newton’s 1st Law (law of inertia) still holds. The light in motion DOES stay in motion in a straight line. It can’t help it that stupid spacetime is bending into massive objects.

PhySP18SS6.3.16 . . .

PhySP18SS6.3.17 Inclined planes. Always tilt your axis and always show your right triangles. Did I ever tell you that a vector at an angle is the hypotenuse of a right triangle?

PhySP18SS6.3.18 same problem.

PhySP18SS6.3.19 A little more complicated. TWO angles.

PhySP18SS6.3.20 The Atomic Chemistry of Friction. On a picometer scale.

PhySP18SS6.3.21 Electrons are really little negative charged bbs like you learn in chemistry. That is a convenience model. Electrons are more like packets of wavelike energy which can only have quantized fundamental frequencies. High energy Electrons can be represented by a short and tight autocorrelated wavelet (top drawing) containing a lot of fundamental frequencies or a lower energy electron can be represented by a more spread out combination of lower fundamental frequencies. The point is, the electron’s location is hard to pin down (part of Heisenberg’s Uncertainty Principle) The more you know about the momentum of the electron, the less you know about the position and vice versa. So these electrons are represented by probability clouds (those shapes you learn in Chemistry). The point is, we don’t really know where any given eelectron is at any given time. Ok, keep that in mind.

PhySP18SS6.3.22 The orbitals of the electrons act like shields around the positive nest of protons in the nucleus. but those shields are not solid. Remember, these electrons are moving around in unpredictable ways so sometimes some of the positive force of the nucleus leaks out beyond the atomic surface of the outermost atoms of a surface.

PhySP18SS6.3.23 This “leakage of + charge” from the proton nest causes the outer electrons in the other surface to move up (because they are attracted to the positive force). They don’t jump the gap, but they do cause that area of the bottom surface to become partial negatively charged. This positive negative attraction is the source of all friction. We call these random temporary attractions between surfaces London Dispersion Forces (LDFs) They were discovered by a scientist with last name London in 1931.

PhySP18SS6.3.24 So why is water such a good lubricant (as you may have noticed if you hav e ever slipped on a slick tile floor)?

PhySP18SS6.3.25 The oxygen of the H2O holds onto the electrons to strong. There are not a lot of loose electrons in a set of water molecules, therefore not as much of a chance for LDFs

PhySP18SS6.3.26 Hydrogen “Bonds” are just about the strongest INTERMOLECULAR bonds there are. That’s why water dominates your body and the world.

PhySP18SS6.3.27 H-Bonds are Dipole-Dipole

PhySP18SS6.3.28 This a micrometer scale view. In a static situation the peaks of one surface settles down into the valleys of another surface. This makes the outer atoms of each surface close enough to each other for many LDFs to form (see Coulomb’s Law).

PhySP18SS6.3.29 So we call this static arrangement between surfaces peak to valley. Look at all those purple LDFs.

PhySP18SS6.3.30

PhySP18SS6.3.31

PhySP18SS6.3.32

PhySP18SS6.3.33 What is two surfaces were perfectly smooth? Then there wouldn’t be any friction right? WRONG!! The friction would skyrocket. Look at all those LDFs forming becasue the surfaces are soooo close to each other. Good luck breaking these two surfaces apart.

PhySP18SS6.3.34 by definition. Notice that the mu sub s and mu sub k are COEFFICIENTS (no units) because the Newtons over Newtons cancel.

PhySP18SS6.3.35 . . .

PhySP18SS6.3.36 Eventhough there are LDFs in both cases above we only show the friction force on the incline because you don’t show a force on a FBD if it has a particular direction. If I tilt a surfac e and the block does not move, the static friction opposes potential motion and now it has a particular direction. See, it needed a purpose to show up. Is that true for all of us? Sorry, getting a little worn out.

PhySP18SS6.3.37 Angle of Repose is the angle of an incline where whatever is sitting on the incline is “JUST ABOUT TO SLIP”.

PhySP18SS6.3.38 We did a theta rep (angle of repose) little 5 minute activity between rough steel and smooth steel and found the thea rep to be about 17°. Now, here’s the cool thing. From knowing that, we can find the coefficient of static friction between the two surfaces.

PhySP18SS6.3.39 some data

PhySP18SS6.3.40 so we need to get from this FBD to the formula at the bottom right.

PhySP18SS6.2.2 First decent angle problem. Notice that everytime you have a force at an angle it is the hypotenuse of a right triangle. You should color in any of those triangles. You won’t ever use the hypotenuse in your calculations (unless you are doing head-to-tail) You will just use the Fx and Fy legs.

PhySP18SS6.2.3 5b and 5c are simply orange equations

PhySP18SS6.2.4 This is from one of the false statements . Remember, Newton’s 3rd law tells you that the forces in a collision between two bodies are equal and opposite, but since F=ma and the masses are different, the accelerations HAVE to be different to keep the forces equal (and opposite).

PhySP18SS6.2.5 Dr. Strauss talked about this crazy notion of considering Energy as the same as mass and he said that that is how all the High Energy Physicists see mass. So, they change the famous E=mc^2 equation into E/c^2 = m; or just say E = mass as long as you change the units of mass from kilograms to Electronvolts. It is an energy unit, however you can use it as a mass unit too because of the famous Einstein relation E=m*c^2. If you are given a mass in eV, you just have to use that formula to get the corresponding mass in real mass units. Strictly speaking it’s a unit of energy. But using m=Ec2, you can convert energy into mass. Operating, we get 1eV/c2=1.78⋅10−36kg. (The c2 is usually ommited.)

PhySP18SS6.2.6 The number of oscillations of the inertial balance is inversely proportional to the mass that is set on the balance because it takes a lot of force to cause the mass on the balance to change directions. The cool thing about an inertial balance os that you would get the same results anywhere in the universe you took the balance as long as the gravitational attraction of the nearest big body was perpendicular to the balance. Since the movement is sideways, gravity play no role. That is why it is called an INERTIAL balance.

PhySP18SS6.2.7 From one of the false statements. When two steel balls of different masses hit each other and bounce off, the forces are equal and opposite, but the accelerations are definitely different since they are inversely related to their mass.

PhySP18SS6.2.8 Same deal as previous slide.

PhySP18SS6.2.9 THis is also from the false statements. Objects near the surface of the earth all have the same acceleration, not the same gravitational force (which we call their weight). See next:

PhySP18SS6.2.10 The Basketball has ten times the greavitational force (weight) oulling it down to earth as the tennis ball, BUT . . . it also has ten times the resistance to move. Therefore the two objects move at the same rate of acceleration in a vacuum.

PhySP18SS6.2.11 Since mass and acceleration are multiplied together to give force in Newton’s 2nd law, they are INVERSELY proportional.

PhySP18SS6.2.12 SO the equation of impulse basically just comes from Newton’s Original 2nd Law.

PhySP18SS6.2.13 Some impulse information

PhySP18SS6.2.14 One type of impulse problem

PhySP18SS6.2.15 . . .

PhySP18SS6.2.16 Impulse is also the area under a Force vs. Time graph.

PhySP18SS6.2.17 . . .

PhySP18SS6.2.18 nTheis is the Impulse graph for a typical symmetric elastic collision. We represent the curve as a triangle because we don’t do Calculus.

PhySP18SS6.2.19 Our approximations

PhySP18SS6.2.20 our approximations

PhySP18SS6.2.21our approximations

PhySP18SS6.2.22 A graphical Impulse problem

PhySP18SS6.2.23 finishing the previous screenshot.

PhySP18SS6.1.2 From the Buoyancy Presentation. We always represent the buoyancy vector as an UP arrow in FBDs.

PhySP18SS6.1.3 From the Buoyancy Presentation Hot air balloons rise because the hot air inside them is less dense than the surrounding “colder” air. The colder air is more dense, but that wouldn’t make the balloon rise. It rises because the air pressure gets higher the closer the air parcel is to the ground because there is more OVERBURDEN on that lower parcel of air than there is on a higher parcel of air. All these air molecules are in Brownian Motion so they slam into any object that is near them. This slamming causes a force. When you take that combined force of trillions of these air molecules over a particular area (like a square inch) you get air pressure. Air pressure in Oklahoma averages about 14.7 psi (lbs per square inch). So more air molecules hit the bottom of the balloon per unit area (causing higher pressure). THere is an increased number of air molecules that are pushing up on the BOTTOM of balloon. So buoyancy is the measure of the extra bit of upward force from these lower outside air molecules.

PhySP18SS6.1.4 From the Buoyancy Presentation. Notice those temps are in celcius. A typical outside temperature is 24°C.

PhySP18SS6.1.5 From the Buoyancy Presentation

PhySP18SS6.1.6 From the Buoyancy Presentation: Archimedes Principle. The mass of a floating object is equal to the of the water the objects displaces. This is a clever way to mass objects! Just figure out the volume of water displaced and multiply by the density of water.

PhySP18SS6.1.7 From the Buoyancy Presentation. Notice is is the amount of SUBMERGED volume, but only if the object is not sinking in the water.

PhySP18SS6.1.8 From the Buoyancy Presentation: So the maximum upward buoyant force that the water can put on this bottle is equal to the whatever the bottle would weigh if it was full of water.

PhySP18SS6.1.9 From the Buoyancy Presentation: From Wiki: The density of ice is 0.9167 g/cm3 at 0 °C, whereas water has a density of 0.9998 g/cm3 at the same temperature. Liquid water is densest, essentially 1.00 g/cm3, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the freezing point is reached. So about 10% of the Iceberg will stick up above the ocean, depending of the temperature and salinity of the ocean water.

PhySP18SS6.1.10 From the Buoyancy Presentation: Archimedes Principle for Mercury (Hg). Hg has a density of about 13.6 g/ml (if I am remembering my chemistry) so it doesn’t take much volume of displaced Hg to equal the mass of the object.

PhySP18SS6.1.11 From the Buoyancy Presentation: How a submarine works. (Know this)

PhySP18SS6.1.12 From the Buoyancy Presentation: More submarine stuff

PhySP18SS6.1.13 From the Buoyancy Presentation: How a fish rises or sinks in water.

PhySP18SS6.1.14 From the Buoyancy Presentation

PhySP18SS6.1.15 From the Buoyancy Presentation: Whales and Sharks adjust the volume of their oil filled livers to rise or sink in water.

PhySP18SS6.1.16 FBDs with angles! Remember to make ever force at an angle the hypotenuse of a right triangle.

PhySP18SS6.1.17 A tennis ball (or any kind of bouncy ball) getting ready to bounce back up after being thrown down. You can do the FBD either way, but I prefer the one on the right. Simpler.

PhySP18SS6.1.18 Ah, our first truly decent Head-To-Tail FBD. We do it Head to Tail so that we can get the lengths right. Then you can redraw it in the traditional FBD diagram where all forces emanate from the center of mass of the object.

PhySP18SS6.1.19 Newton’s 3rd law derived. (Know this)

PhySP18SS6.1.20 Newton’s 3rd Law written out.

PhySP18SS6.1.21 The stopper as it leaves the cannon. When you draw a systewm of bodies you have to indicate the Newton’s 3rd Law pairs.

PhySP18SS6.1.22 Is this an example of Newton’s 3rd Law? Why or why not?

PhySP18SS6.1.23 . . .

PhySP18SS6.1.24 A graphical illustration of Newton’s third law.

PhySP18SS6.1.26 Dr. STRAUSS!! Dr. STRAUSS!!

PhySP18SS6.1.27 Dr. Strauss gave an excellent talk on the LHC. When you start working there, send me a postcard.

PhySP18SS6.1.28 When you use electron Volts for your unit of mass, Einstein’s Equation goes from E = mc^2 to E=m which is so much easier to work with. Plus it reinforces the point that Energy is the same as Mass.

PhySP18SS6.1.29 Fermions (like Protons and Neutrons) are made up of quarks. Always 3 quarks.

PhySP18SS6.1.30 Dr. Strauss told me that they may have found a pentaquark in the LHC. Shhh . . . Nobel Prizes may be coming)

PhySP18SS6.1.31: Newton’s 3rd Law for a fly vs. a Semi truck. The opposing forces are the same, but the masses a vastly different resulting in a huge negative acceleration for the fly. The semi wouldn’t notice their tiny change in velocity.

PhySP18SS6.1.32 Newton’s 3rd Law applied to a sky diver. Felix Bumgarner jumped from about 120,000 ft. so the only force on him as he jumped was the gravitational attraction from the earth. Therefore, he must have pulled the earth up to him. Newton said the EVERY FORCE in the universe has a canceling Newton’s 3rd Law force. Every force comes with its own death. I’m so depressed now.

PhySP18SS6.1.33 So little Felix is not enough to cause the Earth to move much, but what if EVERY man, woman and child jumped out of an airplane (stay with me here, it’s a thought experiment). Would that be enough to move the world? We did the math (back of an envelope) and came to the conclusion that . . . no.

PhySP18SS6.1.34 numbers from another class

PhySP18SS6.1.35 A VERY IMPORTANT PHYSICS PROBLEM. The old 3 Box problem. You will see modifications and complications of this problem your entire Physics career. Look closely at how it was done. I think I have a help video of this on the website.

PhySP18SS6.1.36 A typical FBD / F = ma problem

PhySP18SS6.1.37 a slightly more complicated FBD / ∑F=ma problem

PhySP18SS6.1.38 A little more complicated with Eskima Snow

PhySP18SS6.1.39 It means the world to us teachers that you have our back.

PhySP18SS5.4.1 Time Stamp: Walkout Wednesday. Hope it doesn’t mess up the Test 5B too much.

PhySP18SS5.4.2 Time Stamp. Got to watch Big John in a lead role in the excellent Les Mis at the Sooner Theater.

PhySP18SS5.4.3 Typical day in my advisory. Cooper leads the boys in Folk Songs. They are getting really good with their harmonies.

PhySP18SS5.4.4 There is a whole big explanation of this in the Facebook Group. Search “Inertial” and “Gravitational” probably a good idea to print out that bit from the group and put it in your notebook. Might come in handy in college or the final.

PhySP18SS5.4.5 . . .

PhySP18SS5.4.6 . . .

PhySP18SS5.4.7 Some call this sort of thing a crutch. I call it just another tool for working through a fairly simple physics problem. Sometimes its the simple ones that get you.

PhySP18SS5.4.8 5.10.10a. You see that (as Arnold said), the rocket thrust has to overcome the the force caused by gravitational mass of the rocket (which we call its weight) and the inertial mass (resistance to velocity change) of the rocket represented by the “ma” part of F=ma.

PhySP18SS5.4.9 another slightly different version of 5.10.10a

PhySP18SS5.4.10 This problem is on the THT5B

PhySP18SS5.4.11 yes it IS legal for the d/dt to switch partners. That lil d is a sneaky little stinker.

PhySP18SS5.4.12 Simplified version of the Thrust Equation.

PhySP18SS5.4.13 kg/sec is a weird unit to me, but I guess it makes sense. It is how much mass is being spit out the back of a rocket per second. Usually we keep these units in kg/sec, but it could be any mass over any time.

PhySP18SS5.4.14 messing with the units,

PhySP18SS5.4.15 an example to show you the importance of realizing that the escape velocity (ve) is RELATIVE to the rocket, NOT relaive to the woman watch this whole thing from a reference point.

PhySP18SS5.4.16 All of these are example of Newton’s 2nd Law.

PhySP18SS5.4.17 Mr. Babb’s take on the development of the Thrust Equation from a rocket’s point of view. part 1

PhySP18SS5.4.18 Part 2: A little bit of mass spits out the back of the rocket (dm)

PhySP18SS5.4.19 Part 3: Here he uses Conservation of linear momentum to derive the Thrust Equation. BRILLIANT! Now I wish I had done it this way. So much cooler. I only wish he had replaced the ∆ in the the fourth line on with “lil d” to make all this instantaneous.

PhySP18SS5.4.20 Part 4: So we get the Thrust equation. I wrote about this in the Physics Facebook Group. Notice that there is a second part to the thrust equation. You will need to know this part when you work for Elon Musk at SpaceX. I envy you. He wouldn’t take me. I’m too old and I’m damaged goods. ; )

PhySP18SS5.4.21 All those mean the same thing

PhySP18SS5.4.22 How to attack 5.10.12

PhySP18SS5.4.23 Pretty straight forward 5.9.2

PhySP18SS5.4.24 How to work THT5.13

PhySP18SS5.4.25 Notice all the @s. most of those are on the equation sheets now. This is not true for every car of course. We just have to reach an agreement in the 807.

PhySP18SS5.4.26 Air drag.

PhySP18SS5.4.27 Mean old Robert Brown. Biologist whose mistake changed the world in 1820. He looked through a microscope and thought that the pollen grains were alive because they were randomly moving around. Turns out they figured out later that the pollen grains were not alive (no vis viva). They were simply being bounced around by the water molecules that surrounded them. Turns out the water molecules are ALWAYS moving and bouncing into each other in this chaotic manner. We call it, you guessed it . . . Brownian Motion.

PhySP18SS5.4.29 An illustration of Brownian Motion. High Entropy. meaning that I can not predict where the molecules will be a few seconds after this picture is taken. There is equal chance that they could be anywhere in a three dimensional sphere. This is, by definition, maximum entropy and therefore , the textbook version of Brownian Motion.

PhySP18SS5.4.28 So what does this have to do with the force of lift on a fast moving car? Okay, I’ll give you the simplified non mathematical version of this. This really requires a lot of statistics and Calculus. So I will give you the Reader’s Digest version: All this brownian motion of air molecules (O2 and N2 molecules) cause a standard air pressure (Force per unit area) of 14.7 psi (lbs per square in). This air pressure is at sea level on earth. It tells you that the air molecules have reached maximum entropy and they are bouncing all over the place in all different directions causing little tiny force vectors in all directions.

PhySP18SS5.4.30 Okay . . . so now when there is a breeze (either caused by wind blowing past an object or the object moving through “calm” air, more of the air molecules are flowing in one direction (this is called LAMINAR FLOW). When you are in a laminar flow situation, more air molecules (you can also, of course, do this with water molecules) are flowing in the same direction and the amount of Brownian Motion is reduced. There are less air molecules (or water molecules) to bounce off the sides of a tube they are in so the amount of molecules hitting the side are reduced and therefore the pressure (F/A) is reduced.

PhySP18SS5.4.31 . . .more visuals . .

PhySP18SS5.4.32 . . . more visual info about Laminar flow vs. Brownian motion.

PhySP18SS5.4.33 . . . so what does this have to do with the force of lift on a fast moving car? the faster the laminar flow there is over the top of car (becasue the air molecules have further to go) the less Brownian Motion there is on the top of the car and therefore, the less pressure. basically how an airplane wing works which is great for the airplane, but not good for a car.

PhySP18SS5.4.34 This can be demonstrated with a Venturi Tube.

PhySP18SS5.4.35 it is called the venture effect.

PhySP18SS5.4.36 an example of a venturi tube. Wish I still had mine.

PhySP18SS5.4.37 the same concept is used in perfume bottles.

PhySP18SS5.4.38 The venturi effect is used to increase the speed of escape gases in an F-15 or whatever jet this is.

PhySP18SS5.4.39 We demonstrated it with the old paper hanging from the bottom lip trick.

PhySP18SS5.4.40 Spoilers and Air Dams are how cars deal with lift.

PhySP18SS5.4.41 Cigarette Boats have a real problem with lift.

PhySP18SS5.4.42 So do dragsters

PhySP18SS5.4.43 Modifying the FBD for a car accelerating up to 120mph with the snapshot taken at 80mph

PhySP18SS5.4.44 the same car in neutral slowing down with the snap shot taken at 80mph.

PhySP18SS5.4.45 now slamming on the brakes skidding to a stop with the snapshot taken at 20mph.

PhySP18SS5.4.46 A rocket in the earths lower atmosphere traveling at 75° ALH. Notice there are three forces and a ∑F (because the rocket is Thrusting and accelerating in the DOM.

PhySP18SS5.4.47 An example of the Thrust force being a greater angle than the DOM. It HAS to be because it has to compensate for the weight of the rocket (the downward mg vector)

PhySP18SS5.4.48 another example

PhySP18SS5.4.49 From the Thursday night talk about Neutron stars being used to help us detect gravity waves.

PhySP18SS5.4.50 Most of the crew that went to the talk.