Science (2015) Grade(s): 09-12 - Physical Science

SC15.PS.9

Use mathematical equations (e.g., $(m_1 v_1 + m_2 v_2) _{before} = (m_1 v_1 + m_2 v_2) _{after}$) and diagrams to explain that the total momentum of a system of objects is conserved when there is no net external force on the system.

Unpacked Content

Scientific and Engineering Practices

Using Mathematics and Computational Thinking

Crosscutting Concepts

Energy and Matter

Knowledge

Students know:
  • An object's momentum is a relationship between its mass and velocity.
  • Students know that total momentum of a system of objects is conserved in a collision when no net external forces act on the system.
  • Students know that total mechanical energy of a system of objects is conserved in a one-dimensional elastic collision when no net external forces act on the system.

Skills

Students are able to:
  • Define the system of the two interacting objects mathematically.
  • Define the system of the two interacting objects with diagrams. Infer how momentum is a relationship between mass and velocity of an object, ρ=mv.
  • Identify and describe mathematically the momentum of each object in the system as the product of its mass and its velocity.
  • Use diagrams to model, predict and describe the physical interaction (in an elastic collision) of the two objects in terms of the change in the momentum of each object as a result of the interaction.
  • Use mathematical representations to model, predict and describe the physical interaction (in an elastic collision) of the two objects in terms of the change in the momentum of each object as a result of the interaction.
  • Use mathematical representations to model, predict and describe the physical interaction (in an elastic collision) of the two objects in terms of the change in the mechanical energy of each object as a result of the interaction.

Understanding

Students understand that:
  • If a system interacts with objects outside itself, the total momentum of the system can change; however, any such change is balanced by changes in the momentum of objects outside the system.

Vocabulary

  • Momentum
  • Mass
  • Velocity
  • Elastic collisions
  • Inelastic collisions
  • Conservation of momentum
  • Conservation of mechanical energy
  • External force
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