Conservation of Momentum Derivation and Rocket Demonstration
Conservation of Momentum Derivation and Rocket Demonstration

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Momentum & energy

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Momentum P = mv Momentum is mass in motion Vector quantity Dimensions?

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Force & Momentum Force is the derivative of momentum as a function of time. F = ∆P/∆t = m∆v/∆t Of course ∆v/∆t is accel.

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Momentum Conservation The momentum of a system is always conserved. Complication – P is a vector qty. – which means we will have vector considerations when working w/ P conservation. P o = P f Like relative velocity we have to create the exact formula based on the specific circumstance.

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Scenarios for P conservation Explosion P o = P 1 + P 2 +…. + P n ; exact formula depends on # of pcs. before & after. Collisions –> Explosion P 1o + P 2o = P 1f + P 2f ; exact formula depends on # of pcs. before & after Collision –> Coalescence P 1o + P 2o = P f ; typically here only 2 pcs. collide, see problem #13, p.238

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Energy Exist in 7 forms – crimsen –> cr(h)msen Can be transferred – always involves same form of energy. Can be transformed – involves more than 1 form. Scalar quantity Energy is defined as the ability to do work. Discuss implications.

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Mechanical Energy 2 forms 1) kinetic, 2) potential E k = 1/2mv 2 E p = mgh

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Work W = Fd W = ∆E k W = ∆E p Work like E is a scalar quantity?? Fig. 10-2, p. 258

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Energy Conservation The energy of a system is always conserved. Complication – 7 forms of energy & 2 forms of mech. E. Elastic collision – mech. E conserved Inelastic collision – mech. E is not conserved. Falling body – E po = E kf Exact form of E conservation eq. Is circumstance dependent.

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P & E conservation Occurring to every system @ the same time. Complicated b/c P is vector & E is scalar & b/c energy exist in 7 forms.

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