Lec11_Sum_f - Summary Lecture 11 Conservative forces: the...

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1 Lecture 11 Linear Momentum Conservation of Linear Momentum Impulse Physics 111, Summer 2011, June 30, Lecture 11 Summary Nonconservative forces : the work done depends on the pass taken (e.g. friction force). Conservative forces : the work done does not depend on the pass taken but only on the initial and final positions (e.g. gravitational force). Law of conservation of energy: The total energy of an isolated system is constant (conserved): Mechanical energy is the sum of potential and kinetic energies. If only conservative forces are acting, the total mechanic energy is conserved: 1 1 2 2 PE KE PE KE + = + const E E = = 1 2 const E total = t i f d t h t t l h i 2 Average power in terms of force and average speed : v F P = Power is work done over used time; the unit of power is watt (W = J/s): t W t work P = = Nonconservative forces reduce the total mechanic energy. Physics 111, Summer 2011, June 30, Lecture 11 We will define a quantity called “linear momentum” which incorporates the ideas of mass and velocity . Linear Momentum Linear momentum is the product of the mass and the velocity of an object: elocity ass omentum near = v - an object at rest has zero linear momentum; - a heavy object moving quickly has a large linear momentum; - a light object has smaller linear momentum that a heavy object moving at the same speed. velocity mass momentum linear × mv p = Like velocity, linear momentum is a vector quantity. The unit of linear momentum: (kg)(m/s)= kg·m/s v m p = r 3 Physics 111, Summer 2011, June 30, Lecture 11 Linear Momentum A car with a mass of 1200 kg has a speed of 60 miles/hour. Find the linear momentum of the car. 1. Conversion of miles/hour to m/s: s m h s mi m h mi hour miles / 83 . 26 3600 1610 60 60 = = Linear momentum of the car: 4 mv p = s m kg s m kg p 196 32 ) / 83 . 26 )( 1200 ( = = 2. Linear momentum of the car: Physics 111, Summer 2011, June 30, Lecture 11
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2 Linear Momentum and Newton’s Second Law 2 nd Newton’s law for any object: a m F r r = t v a Δ Δ = r r Definition of acceleration: Definition of linear momentum: r r = t v m t v
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Lec11_Sum_f - Summary Lecture 11 Conservative forces: the...

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