Many pupils who do recognise that forces arise in pairs think that the two forces in a pair may differ in size.

Forces and Motion


For instance, pupils may think that a larger object exerts a bigger force on a smaller object than vice versa.

Resources to Address This

  • Describing interactions (14-16)

    Source - SPT/ Fm04TA04

    This resource provides a discussion framework for analysing interactions between objects.

    View Resource
  • Forces exerted by distorted solids (5-11)

    Source - SPT/ Mf03PN02

    Compression and tension forces that create a balanced situation.

    View Resource


The following studies have documented this misconception:

  • Gunstone, R. F. and White, R. T. () Understanding of Gravity. Science Education, 65 (3),


    This study presented a sample of first year physics undergraduates at Monash University, Australia, with eight physical situations. The students were asked to make predictions as to what would happen if a certain action was taken. The action was then taken, and the subjects were asked to explain any discrepancies between their prediction and the result.
    Review sheet

  • Brown, D. and Clement, J. () "Classroom Teaching Experiments in Mechanics" in R. Duit, F. Goldberg, & H. Niedderer (Eds.), Research in physics learning - theoretical issues and empirical studies. San Diego State University, San Diego, CA.


    Review sheet

IOP DOMAINS Physics CPD programme

Electricity CPD videos

Our new set of videos gives teachers and coaches of physics a preview of the training we offer ahead of this term's live support sessions.

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