Lec17

# Lec17 - Physics 2A Lecture 17 "If you can find a path with...

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Physics 2A Lecture 17 "If you can find a path with no obstacles, it probably doesn't lead anywhere.” --Frank A. Clark

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Newton’s Laws COM Since the center of mass is now calculable, we can use this to describe the motion of complicated objects. We will treat complicated objects as point particles with all of the forces acting at the location of the center of mass. F gravity Newton’s 2nd Law can be written as: r F = M r a COM where M = total mass. Σ F are external forces to the system. a COM is the acceleration of the center of mass.
Linear Momentum COM Recall from earlier in the quarter, we deﬁned linear momentum, p, as a vector that measures your motion: The units of momentum are: [kg m/s] As we mentioned before, the correct form of Newton’s Second Law is: If the mass is constant: r p = m r v r F = d r p dt r F = d r p dt = d m r v ( ) dt = m d r v dt = m r a

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Momentum If we have a system of particles or a complicated body: So, essentially, if there is no net external force present upon a system; then its momentum will remain constant. r p com = M r v com where M is the mass of the total system and v com is the velocity of the center of mass. We can extend Newton’s Second Law to complicated systems via: r F ext = d r p com dt
Momentum Mathematically we say: This is the law of conservation of momentum.

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## This note was uploaded on 07/25/2009 for the course PHYS 2A taught by Professor Hicks during the Winter '07 term at UCSD.

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Lec17 - Physics 2A Lecture 17 "If you can find a path with...

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