Momentum

• All moving objects have momentum but if an object is not moving then its momentum is zero
• Momentum

  Mass multiplied by velocity
• The unit of momentum is kilograms meter per second
• Calculating momentum


  • Car with mass 1,000 kg and not moving: momentum = 0
  • Car with mass 1,000 kg and moving at 20 m/s: momentum = 20,000 kg m/s
• Conservation of momentum


  In a closed system, the total momentum before an event is equal to the total momentum after an event
• Example 1: Van colliding with stationary car


  1. Van has momentum before collision

  2. Van and car move together at lower velocity after collision

  3. Total momentum before = total momentum after
• Example 2: Cannon firing cannonball


  1. Cannon and cannonball have zero momentum before firing

  2. Cannonball has forward momentum after firing

  3. Cannon has backward momentum after firing

  4. Total momentum before = total momentum after = 0
• Momentum

  A property that all moving objects have
• Momentum

  Mass of an object multiplied by its velocity
• Momentum of objects

  • 4,500 kg dinosaur at 12 m/s = 54,000 kg·m/s
  • 1,200 kg car at 25 m/s = 30,000 kg·m/s
• Momentum

  • A vector quantity with both magnitude and direction
• Conservation of momentum principle

  In a closed system, the total momentum before an event is the same as the total momentum after the event
• Finding velocity after collision

  1. Find total momentum before collision

  2. Use conservation of momentum principle

  3. Rearrange momentum equation to find velocity
• Stationary object's momentum

  Zero
• Finding gun recoil velocity

  1. Find bullet momentum

  2. Set gun momentum + bullet momentum = 0

  3. Rearrange equation to find gun velocity
• Momentum equation

  p = mv