AP Physics 1 Review: Impulse and Momentum

Key Concepts

• Impulse

  • Acts on an object to change its momentum.
  • Related to the force and the time that force acts on an object.

• Momentum

  • A conserved quantity in a closed system.
  • Measures mass in motion, denoted by p.
  • Equation: ( p = mv ) (momentum = mass x velocity).
  • It's a vector quantity, same direction as velocity.

Momentum and Impulse

• To change velocity, a net force must act on the object.
• Newton's Second Law rearranged for momentum: ( \Delta p = F_{net} \times \Delta t )
  • ( \Delta p ): Change in momentum
  • ( F_{net} ): Net force
  • ( \Delta t ): Time interval
• Impulse-Momentum Theorem: Change in momentum = Impulse.
  • Applicable when a single large force acts on an object.

Action-Reaction Pairs

• Impulses also form action-reaction pairs.
  • Example: Tennis racket and ball, bumper cars.

Conservation of Momentum

• In a closed system, total momentum remains constant.
  • Applicable in collisions and explosions.
• Equation: ( m_1v_1 + m_2v_2 = m_1v_1' + m_2v_2' )
  • Apply separately in x and y directions if two-dimensional.

Force-Time Graphs

• Area under graph represents impulse.
  • Rectangle: Constant force, ( F \times t )
  • Triangle: Varies, area still represents impulse.
• Safety applications: Airbags increase time, reducing force.

Examples

• Ping Pong Ball Example

  • Different surfaces affect the bounce and impulse.
  • Larger change in momentum when the ball bounces than when it stops.

• Toy Car and Truck Collision

  • Conservation of momentum used to solve for post-collision velocities.
  • Elastic vs Inelastic Collisions:
    • Elastic: Kinetic energy is conserved.
    • Inelastic: Objects stick together.

• Carlos, Angela, and Bowling Ball Example

  • Illustrates conservation of momentum and impulse.
  • Carlos moves faster due to less mass compared to Angela and the ball.

Key Takeaways

• Visualize momentum changes with motion diagrams before and after events.
• Impulse and change in momentum are interchangeable; use appropriately.
• The impulse-momentum theorem is for a single object, while conservation of momentum is for closed systems.
• Remember momentum is a vector; consider direction and signs.

Conclusion

• Be confident in your understanding of momentum and impulse for AP Physics 1.
• Good luck on your exams!