Momentum

• What is momentum?

  The product of mass and velocity
• Is momentum a scalar or vector quantity?

  Vector - Has both a magnitude and direction
• State an example of Momentum:

  • An elephant has no momentum when it is standing still.
  • When it begins to walk, it will have momentum in the same direction as it is travelling
  • The faster the elephant walks, the larger it's momentum will be
• State the equation of momentum

  Momentum = mass x velocity (measures in kg m/s)
• In a closed system:

  Total momentum before an event = Total momentum after the event
• What is a closed system?

  Something that is not affected by external forces (Conservation of Momentum)
• Momentum is conserved in...

  Collisions and explosions
• Why does a cannon recoil backwards when it is fired?

  • The cannon ball gains forward momentum and the cannon gains backward momentum
  • Before the cannon is fired, the total momentum of the cannon is zero because neither object is moving
  • The total momentum of the cannon and ball after being fired is also zero because the cannon and cannon ball moves in opposite directions
• State the method of investigating how force affects acceleration

  1. Position an air track on a bench with a bench pulley at one end and two light gates above the track. Cut and interrupt card to a known length (e.g 10 cm), and attach is to an air track glider
  2. Connect the glider to a hanging mass by a string the length of the air track passing over the bench pulley.
  3. Set the data logging software to calculate acceleration
  4. Add 5 x 20g slotted masses (0.98 N of force) to the end of the string
  5. Release the glider, then record the weight and acceleration
  6. Repeat steps 4 and 5 two more times, and calculate a mean value for the acceleration
  7. Repeat steps 4 to 6, removing one of the slotted masses each time
• How would you change the practical to investigate how mass affects acceleration?

  Use the same practical for force affecting acceleration, but use 100g of force for every run, adding increasing numbers of slotted masses to the glider

  Record the total mass of the glider and hanging masses combined
• Acceleration is...

  Inversely proportional to mass
• Acceleration is...

  Directly proportional to force