Week Before Spring Break
Week Before Spring Break Physics 120-01
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This 3 page Class Notes was uploaded by Alexandra Graham on Sunday March 22, 2015. The Class Notes belongs to Physics 120-01 at University of Massachusetts taught by Guy Blaylock in Spring2015. Since its upload, it has received 92 views. For similar materials see Big Bang to Black Hole in Physics 2 at University of Massachusetts.
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Date Created: 03/22/15
Physics Notes March 913 39 Would it hurt to fall into a black hole As you fall into a BH you are squeezed and stretched by tidal forces Tidal forces are what rst made Einstein consider curved spacetime As an object falls towards a spherical mass it feels forces in its frame that squeeze it side ways and stretch it length wise Theoretically there39s another way for how spacetime can take form A wormhole Great diagrams in slides Spacetime that curves in and then back out again Mathematically allowable but no one knows if physically possible 0 You couldn39t send a signal through it since even a light beam can39t make it through a wormhole before it closes itself off It is theoretically possible though Math says you can hold spacetime open with a negative energy material Then you39ve got a shortcut through spacetime Now two important effects The Geodetic Effect If you carry a stick around a closed path in at space taking care to point it always in the same direction the stick will return to starting point with no change in direction In curved space a stick can arrive at the starting point having rotated during the trip Frame Dragging Mass and energy tell spacetime how to curve spacetime tells massenergy how to move They39re connected If mass and energy are accelerating then spacetime gets dragged with it A nearby object would also be pulled along and rotated This is an incredibly tiny affect we can barely measure it 311 Review Geodetic effect stick changes direction if you move in a curved space Frame dragging spacetime near a spinning mass is dragged along with the motion of the mass and objects in that spacetime will also spin The Awesome Experiment That Proves These 2 Things GRAVITY PROBE B 0 Leonard Schiff Stanford physicist who came up with idea Took over 50 years to build and analyze o 1960 devised 2004 launched 2011 results nally published Tests geodetic effect and frame dragging Here39s the deal 1 As a gyroscope orbits the earth it will rotate due to geodesic effect 2 As long as it is near the earth in orbit or not it will rotate due to frame dragging The problems How to make a perfect gyroscope How do you get rid of the effects of Earth39s magnetic eld How would one keep it all at the temperature of liquid helium The Gyroscope More clearly explained in slides but basically created a SQUID superconducting quantum interference device coated a perfect sphere in niobium a superconducting aka allows electrons to move completely freely material 313 Remember frame dragging if massenergy are accelerating then space time is dragged along with it Gravity Probe B Cont39d For all this to work you have to put the perfect gyroscope in a verv riaid verv stable structure What they did housing made of fused quartz using optical lensing A Lesson on Friction to understand Optical Lensing Friction increases as you try to push a book across a table but as soon as you get it moving it feels like the opposing friction has lessened It39s harder to get something moving than to keep it moving 0 Static Friction force of friction when the book is not sliding there is no motion 0 Kinetic Friction force of friction when it is sliding there is motion But why is this 0 Going from static friction to kinetic friction requires breaking atomic bonds Kinetic friction is lesser because the movement prevents atoms from attracting each other So stuff is constantly bonding whv don39t two surfaces fuse tooether Even smooth surfaces are actually rough on a microscopic scale There are bumps and nooks and crannies so when you get small enough you see that really two surfaces hardly touch at all But sometimes they do Which leads us to EXTREME FRICTION Super super super super super smooth surfaces on an atomic scale This is achievable with crystals Cut crystal materials along a lattice plane to get perfectly at surfaces then stick them together GUESS WHAT THEY FUSE Guess what else You can do this with fused quartz Which is exactly what they did to make the housing unit for the perfect gyroscope in Gravity Probe B But yet another problem How do you get rid of the Earth39s magnetic eld You ve got a magnetized gyroscope it39ll move in a magnetic eld You put it in a superconducting insulator Electrons can move in a superconductor with no impedance so naturally cancels magnetic elds 0 They hilariously put it inside a lead balloon So they39re pretty much ready now except how to support the gyroscope and get it into space with no torque or friction Orbit is free fall so that s ne but getting it there they had to steer the spacecraft around the gyroscope Lawlz FINALLY Launched in 3904 with a launch window of ONE SECOND 1 sec but made it it orbited for a year and then they analyzed everything and published it all in 3911 IT CONFIRMED BOTH EFFECTS HOLLA
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