Review #1
Physics 102.002September 17, 2007Prof. Michael Gold
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Motion
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Newton’s Laws
Newton (I) II: inertial mass, force,
Newton III: interaction between two objects,
force of 1 on 2
is equal and opposite to
force of 2 on 1
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Newtonian Gravity
Universal Law:
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Kepler’s Laws
3. Period and semi-major axis
2. Motion along ellipse “equal areasin equal times” (conservation ofangular momentum)
1. Planets move in elliptical orbitswith sun at one focus
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Kinetic Energy and Work
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Momentum
Equivalent to Newton III
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Mechanical EnergyPotential Energy defined for conservative force:
Examples: Gravity, (ideal) spring
Counter Example: friction
Near earth’s surface
For (ideal) spring (k measures springstrength
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Conservation of MechanicalEnergy
If only conservative forcesare present,
E = T + UIs conserved. Sum of kineticand potential energy doesnot change.
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Angular Momentum
Moment of inertia I defined as
Sum of mass x (distance to rotation axis)2
Angular momentum is product of moment ofinertia and angular speed
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Rotational Kinetic Energy
Note similarity between linear andangular momentum, kinetic energy
Mass => moment of inertia
Speed => angular speed
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Work Example: part ICentripetal force does no workbecause force is perpendicular todisplacement
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Work example part IIWhile spiraling in velocity isnot perpendicular to force
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Algebra
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Simple Harmonic Motion
For spring or simple pendulum,Force prop-to displacementU = 1/2 (const) (displacement)2
Sketch ofU (parabola)
E
displacement
Turningpoints