Many students think conservation of momentum in collisions applies only when objects visibly move post-collision.

Forces and Motion


Students may struggle to apply the principle to situations where one object does not appear to move, such as a snowball colliding with a wall. 

Resources that Address This

  • Investigating momentum during collisions (11-16)

    A moving glider on a linear air track collides with a stationary glider, thus giving it some momentum. This data-logging experiment explores the relationship between the momentum of the initially moving glider and the momentum of both gliders after the collision. 

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  • Episode 220: Momentum and its conservation (16-19)

    This episode introduces the concept of momentum and its conservation - using a number of different examples.

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The following studies have documented this misconception:

  • Clement, J. () "Students' alternative conceptions in mechanics: a coherent system of preconceptions?" In H. Helm, and J. D. Novak (Eds.), Proceedings of the International Seminar: Misconceptions in Science and Mathematics. Cornell University, Ithaca, NY, 310-315.

    This study highlighted common ideas among students, including the idea that a force can be used up; a force inside a moving object is what keeps it going and if there is motion, there must be a force in the direction of motion. They suggest teachers develop metaphors which organise intuitions the student already has.

    Paper digest

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