Introduction to Momentum

What is Momentum?

• Described as "mass in motion."
• Calculated as the product of mass and velocity:
  • Formula: ( p = m \times v )
  • Mass in kilograms (kg)
  • Velocity in meters per second (m/s)
  • Unit: kg m/s
• Momentum is a vector (direction matters).

Change in Momentum

• Occurs when there is a change in velocity:
  • Speed up, slow down, or change direction.
• If velocity changes, momentum changes.
  • Change in momentum is represented as:
    • ( \Delta p = m(v_f - v_i) )
    • Final momentum minus initial momentum.

Calculations and Examples

• Example 1: 5 kg block moving left at 2 m/s:
  • Momentum = 10 kg m/s (left)
  • Important to include direction.
• Example 2: Car traveling east:
  • Mass = 600 kg, initial velocity = 20 m/s, final velocity = 24 m/s.
  • Change in momentum = 2400 kg m/s (east).
• Example 3: 3 kg block on frictionless path:
  • Initial velocity = 1.5 m/s, final velocity = 1 m/s.
  • Change in momentum = -1.5 kg m/s (opposite direction).
• Example 4: 100g tennis ball hits wall:
  • Convert mass to kg: 100g = 0.1 kg.
  • Initial velocity = 10 m/s (toward wall), final velocity = 8 m/s (away from wall).
  • Change in momentum = -1.8 kg m/s (away from wall).

Key Points

• Direction: Always state direction in vectors.
• Sign Convention: Define positive and negative directions; consistency is crucial.
• Formula Use: Write formulas as given on the formula sheet in exams.
• Convert units where necessary (e.g., grams to kilograms).

Practical Applications

• Understanding momentum and change in momentum is critical for studying impulse and impulse momentum in future sections.