Year 11 Physics - Momentum Notes

Year 11 Physics - Momentum Notes

Class Schedule

  • 10:00am Start
  • 10:00-10:55am Teaching
  • 10:55-11:05am Morning Break
  • 11:05-12:30pm Teaching
  • 12:30-1:30pm Lunch
  • 1:30-2:15 Teaching
  • 2:15-2:20pm Afternoon Break
  • 2:20-3:00pm Teaching
  • 3:00pm Finish

Learning Objectives

  1. Define momentum and conservation of momentum.
  2. Use the equation:
    ext{momentum} = ext{mass} imes ext{velocity}
  3. Understand that in a closed system, the total momentum before an event equals the total momentum after the event.
  4. Describe, explain, and perform calculations of the momentum in an event.

Definition of Momentum

  • Momentum is defined as the product of mass and velocity: p = mv
    • Where:
    • p = momentum (kg m/s)
    • m = mass (kg)
    • v = velocity (m/s)

Conservation of Momentum

  • In a closed system, the total momentum before an event is equal to the total momentum after the event.
  • This principle applies to collisions and explosions.

Example Calculations

Worked Example 1
  • A car has a mass of 1200 kg and is travelling at 15 m/s.
    • Momentum:
      p = 1200 imes 15 = 18000 ext{ kg m/s}
Worked Example 2
  • A second car has a mass of 1000 kg and is stationary:
    • Momentum:
      p = 1000 imes 0 = 0 ext{ kg m/s}

Characteristics of Momentum

  • Vector Quantity: Momentum has both magnitude and direction.
  • An object in motion has a tendency to keep moving in its direction (inertia).
  • The greater the momentum, the harder it is to stop.

Effects of Change in Velocity and Direction

  • Momentum depends on the mass and direction of the object.
  • An increase in speed or a change in direction alters momentum.

Conservation of Momentum in Collisions

  • The total momentum before a collision equals the total momentum after the collision. This can be exemplified with practical experiments (like cart collisions in a lab).

Changes in Momentum

  • When a force acts on a moving object, it results in a change of momentum. The formula:
    F = m rac{ ext{change in momentum}}{ ext{time}}
Impact Duration and Force Relationship
  • Increasing impact time reduces impact force.
  • Forces are inversely proportional to crashing times.

Safety Features in Vehicles and Playgrounds

  • Safety features like airbags and seat belts increase impact time, which decreases the force experienced by passengers during collisions.
  • Playground surfaces are cushioned to extend the impact time when falling.

Worked Examples on Safety Features

  1. Collision of Cars:
    • Car 1: mass = 1000 kg, velocity before = 10 m/s
    • Car 2: mass = 1500 kg, velocity = 0 m/s
    • Momentum calculations before and after teach the importance of safety engineering.
  2. Cushioned Surfaces:
    • When a child falls on a cushioned surface, the time to come to rest is longer, minimizing force impact.

Summary of Key Equations

  1. Momentum:
    p = mv
  2. Conservation of Momentum:
    ext{Total momentum before} = ext{Total momentum after}
  3. Change in momentum formulation:
    F = m rac{ ext{change in velocity}}{time}
  4. Implications of momentum on safety: increased impact time leads to reduced force, crucial for vehicle design and safety systems.