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BYU - PHY S 100 - Class Notes - Week 5

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BYU - PHY S 100 - Class Notes - Week 5

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background image Chapter 8: Conservation Laws *Conserved quantity: quantity that remains constant during a process*  
Conservation of Mass
In most cases, the weight of the "reactants" (what you start with) equals the  weight of the products (what you end with), even with different heat and time 
Mass can change its form or transfer from one place to another This law used in chemical processes like the Carbon Cycle to track the masses of
molecules in the air, in plants, and in
Conservation of Fundamental Particles Similar to conservation of mass--number of atoms remains the same in  chemical processes (same number of atoms of each element at the beginning 
and the end)
Fundamental particles discovered
Leptons: electrons (can't be broken down) and electron-like particles  i. Electrons, muons, tauons, three types of neutrinos + anti- particles for each of those ii. Conservation of lepton number: leptons can change into other  leptons, but the total number of leptons is constant 2 Quarks: make up protons and neutrons i. Quarks cannot be separated from proton/neutron BUT can be  transformed to create a proton or neutron 1. 3 quarks = proton    3 quarks = neutron ii Total number of quarks does not change iii Conservation of atomic mass number:  total number of protons and 
neutrons stays the same
*Illustration: Hold up four fingers from each hand. The ones are your 
right hand (RH) are your protons. The ones on your left are your 
neutrons. Notice each finger is made up of three segments; three 
quarks make up a proton/neutron. Four protons and four neutrons--
twelve quarks on each side. Now lower your pinkie on your left. Add 
your thumb on your right. The quarks from your left pinkie changed 
and made an extra proton. Now you have three neutrons and five 
protons. Atomic mass number is the same before and after the 
change: 8. 
Before: 4 + 4 = 8 
After: 3 + 5 = 8 
background image   Conservation of Charge Positive and negative charges are not created, but simply redistributed Electrons move easily between objects o Example: sliding across carpet in rubber shoes The rubber on your shoes is taking electrons from the carpet  (you are now negatively-charged--extra electrons--and the carpet is 
now positively charged--fewer electrons)
Electrons are transferred, but the total charge (protons + neutrons +  electrons) is the SAME   Conservation of Linear Momentum Linear momentum: mass of an object times its velocity (m * v) o Amount of motion in a straight line If the object is shattered into shards, we can multiply the mass of each  fragment to its velocity, then added up to the other shards' momentum (it will 
be equal to total mass * velocity)
o 4 * 5 = 20     1*5 + 1*5 + 1*5 + 1*5 = 20    2*2.5 + 4*1.25 + 1*5 +  1*5 = 20  Used to determine speed and direction of two objects after collision (like car  crashes) The momentum of an object before change (like collision) is the same as the  momentum of fragments of the object   Conservation of Linear Momentum at High Speeds *Spaceship analogy on pg. 100--conservation of momentum isn't applying here like 
it should!*
Emmy Noether (1182-1935) demonstrated that conservation of momentum  also follows position symmetry o Position symmetry (Chapter 1): if the law applies on earth, then it  applies across the universe Mass increases at high speeds; same momentum, but because of an  increasing mass, more force is required to accelerate that object o Momentum = Increasing mass * decreasing velocity --> same  momentum before and after   Conservation of Angular Momentum Angular momentum: the amount of rotational motion in an object o Keeps you on the bike when you pedal faster! Angular momentum = mass * speed * radius o If you tighten the circle (decrease the radius), the speed must increase  as well so the angular momentum is the same  Without any outside forces, object will keep its angular momentum o Bike stays upright far easier when in motion than at rest   Conservation of Energy

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School: Brigham Young University
Department: OTHER
Course: Physical Science
Professor: Patricia Ackroyd
Term: Spring 2017
Tags: Physics and conservation
Name: Chapter 8 Notes Week 5
Description: Conservations Laws
Uploaded: 10/13/2017
3 Pages 29 Views 23 Unlocks
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