Many students think conservation of momentum in collisions applies only when objects visibly move postcollision.
Misconception
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 (1116)
A moving glider on a linear air track collides with a stationary glider, thus giving it some momentum. This datalogging 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 (1619)
This episode introduces the concept of momentum and its conservation  using a number of different examples.
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References
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, 310315.
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.
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