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# chapter4 - Chapter 4 Forces and Mass Classical Mechanics...

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Chapter 4 Chapter 4 Forces and Mass

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Classical Mechanics Classical Mechanics does not apply for very tiny objects (< atomic sizes) objects moving near the speed of light
Newton’s First Law Newton’s First Law If the net force  F exerted on an object is zero the  object continues in its original state of motion. That  is, if  F = 0, an object at rest remains at rest and an  object moving with some velocity continues with the  same velocity. Contrast with Aristotle!

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Forces Forces Usually a push or pull Vector Either contact or field force
Contact and Field Forces Contact and Field Forces

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Fundamental (Field) Forces Fundamental (Field) Forces Types Strong nuclear force Electromagnetic force Weak nuclear force Gravity
Strong Nuclear Force Strong Nuclear Force QCD (Quantum chromodynamics) confines quarks by exchaning gluons Nuclear force: binds protons and neutrons by exchanging pions

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Electromagnetic Forces Electromagnetic Forces  Opposites attract, like-signs repel  Electric forces bind electrons in atoms  Magnetic forces arise from moving charges
Weak Nuclear Force Weak Nuclear Force Involves exchange of heavy W or Z particle Responsible for decay of neutrons

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Gravity Gravity Attractive force between any two bodies Proportional to both masses Inversely proportional to square of distance F = G m 1 m 2 r 2
Inertia (Newton’s First Law) Inertia (Newton’s First Law) Tendency of an object to continue in its original  motion

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Mass Mass A measure of the resistance of an object to changes in  its motion due to a force Scalar SI units are kg
Newton’s Second Law Newton’s Second Law Acceleration is proportional to net force and inversely  proportional to mass. r F е = m r a

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Units of Force Units of Force SI unit is Newton (N) US Customary unit is pound (lb) 1 N = 0.225 lb F = ma 1 N = 1 kg Ч m s 2
Weight Weight Weight is magnitude of gravitational force  w = mg w = G M earth m r 2 g = GM earth R earth 2 weight mass

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Weight vs. Mass Weight vs. Mass Mass is inherent property Weight depends on location
Newton’s Third Law Newton’s Third Law Single isolated force cannot exist For every action there is an equal and opposite  reaction Force on “1” due to “2” r F 12 =- r F 21

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Newton’s Third Law cont.
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chapter4 - Chapter 4 Forces and Mass Classical Mechanics...

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