Science-G9-W1

• Momentum


  The product of an object's mass and velocity
• Conservation of momentum


  • In the absence of an external force, the momentum of the system remains unchanged
• Conservation of momentum


  1. Total initial momentum = Total final momentum

  2. m1v1(initial) + m2v2(initial) = m1v1(final) + m2v2(final)
• Situations where conservation of momentum applies

  • Car crash
  • Two ice skaters pushing each other
  • Rocket launching
  • Billiard games
• An external force is required to change the momentum of a body, but action and reaction forces acting within do not affect any change in the momentum of the body
• If no external force acts on a body, its momentum will not change
• Momentum conservation


  The total momentum before a collision is equal to the total momentum after a collision
• The momentum gained by one object in a collision is of equal magnitude but opposite direction to the momentum gained by the other object
• Solving conservation of momentum problems

  1. Write the equation for conservation of momentum

  2. Substitute the given values

  3. Solve for the unknown
• Sample problems on conservation of momentum

  • Collision of two trucks
  • Collision of two identical balls
  • Two ice skaters pushing off
• The velocity of the blue ball after collision is 0.5 m/s
• The momentum of the boy-girl system is conserved
• There is no change in the momentum of the system before and after the push off
• The mass of the girl is 46 kilograms
• Lighter skateboarder


  65 kg
• Heavier skateboarder


  85 kg
• Lighter skateboarder velocity


  3.2 m/s
• The momentum of an isolated system is always conserved no matter what kind of force is acting inside the system
• If the velocity of a single particle is zero, its momentum must be zero
• Rockets work on the principle of conservation of momentum
• The total momentum before a collision is equal to the total momentum after a collision
• Mass and velocity affect the momentum of the body
• Ball 1


  Mass 25 g, Velocity 30 cm/s southward
• Ball 2


  Mass 10 g, Velocity 15 cm/s southward
• Ball 1 after collision


  Velocity 22 cm/s southward