# Some students confuse friction and the normal reaction

Forces and Motion

Misconception

They likely do this as both arise from an interaction between an object and the surface it is sitting on.

More generally, students may confuse Newton's first and third laws because they do not recognise that the forces in an interaction pair always act on different objects, and confuse the balanced forces on a stationary object (such as a box sitting on the floor) with the equal forces of an interaction pair.

### Diagnostic Resources

• Friction

This resource gives an accessible explanation of friction.

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• Friction between solid surfaces (11-16)

Part 3 of this resource explores the idea of normal force.

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• Episode 214: Work done by a force (16-19)

Activity 214-1 explores work done in raising a weight using a ramp. The explanation included=s both friction and normal force.

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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, 310-315.

This study highlighted common ideas among students, including the ideas 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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