Terry, Jones and Hurford (1985)

This Welsh study (a collaboration between two heads of physics and researchers) aims to establish the intuitive ways secondary students explain equilibrium forces on an object. A simple scenario was analysed by 153 students ages 14-16 to establish what the student understood about the forces acting on an object resting on a table. 

Evidence-based suggestions

Use structured discussions to help children identify the correct forces on objects in equilibrium, such as recognising that a table exerts the necessary force on a resting box to prevent its acceleration.

Learners’ ideas

  • Students could not analyse simple situations involving multiple forces acting on an object at rest. 
  • Students thought the table didn't need to exert a force on the box when at rest on a desk.
  • Younger pupils could only identify one force acting on the box (gravity).
  • Some students think gravity acts from above an object (i.e. it is pushed down).
  • Students do not understand how an inanimate object can exert a force.
  • Students did not know where to place arrows on the force diagrams.

Further suggestions

  • For pupils to understand force and motion, they must first understand forces acting on an object to keep it at rest.
  • The relationship between a push (or pull) and the effect of the force on the object should be made clear.
  • Teaching strategies should emphasise the consequences of balanced and unbalanced forces acting on an object, using examples of objects in motion and at rest for both.
  • Teachers should avoid using the phrase "force of gravity" as this confuses students.

Study Structure


To identify teaching strategies that might enhance children's conceptual development in forces and equilibrium.

Evidence collection

Students were presented with a box-on-a-table scenario and were asked to describe and explain it in terms of the forces acting. They were also asked to draw diagrams of the forces and name them. The percentage of students that could explain the scenario was recorded.

Details of the sample

A convenience sample of 153 students (aged 14 – 16) was drawn from two secondary schools in north Wales in three different year groups (57 in year 9, 46 in year 10 and 55 in year 11).

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