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7.1 Momentum and Force Linear momentum of an object: Apply Newton’s 2 nd Law of Motion

7.1 Momentum and Force Linear momentum of an object: Apply Newton’s 2 nd Law of Motion. 7.2 Conservation of Momentum From Newton’s 3 rd Law: Δ p A = Δ p B m A v A + m B v B = m A v´ A + m B v´ B. 7.2 Conservation of Momentum (M+ Δ m)v = M(v+ Δ v) + Δ m(v-v e )

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7.1 Momentum and Force Linear momentum of an object: Apply Newton’s 2 nd Law of Motion

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  1. 7.1 Momentum and Force • Linear momentum of an object: • Apply Newton’s 2nd Law of Motion APHY201

  2. 7.2 Conservation of Momentum • From Newton’s 3rd Law: ΔpA = ΔpB mAvA + mBvB = mAv´A + mBv´B APHY201

  3. 7.2 Conservation of Momentum (M+Δm)v = M(v+Δv) + Δm(v-ve) M Δv = Δm(ve) Since Δm = - ΔM M Δv = -veΔM ve APHY201

  4. 7.3 Collisions and Impulse • Impulse = change in momentum • F and Δt combinations APHY201

  5. 7.3 Collisions and Impulse • Threshold for bone fracture ~ 90,000 N ~ 20,000 lb • Whole-body impact limit < 2 x 105 N/m2 (28 lb/in2) • Rapid acceleration can damage spinal cord without fracture • Airbags and seatbelts increase Δt and reduce F • Crumple zones – absorbing the initial KE APHY201

  6. 7.4 Conservation of Energy and Momentum in Collisions • For elastic: KEi = KEf • For inelastic: KEi = KEf + Eother APHY201

  7. In class: Questions 1, 2 and Problem 4 • Other problems ↓ 6. Let “A” represent the halfback, and “B” represent the tackling cornerback. APHY201

  8. 16. (a) The impulse given to the nail is the opposite of the impulse given to the hammer. This is the change in momentum. Call the direction of the initial velocity of the hammer the positive direction. (b) The average force is the impulse divided by the time of contact. APHY201

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