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.