Student Conception: Cause of falling

[Matt Anthes-Washburn]

Student Conception: Cause of falling
Students do not associate falling objects with a causation force. ((Driver, R. et al., (1994) Making Sense of Science; research into children’s ideas. Routledge, London  pp. 165), Stead and Osborne, Ruggiero et al.)

Identifiers
Students will say that objects just fall.  They will not identify a force that causes the object to fall.

Confounding Experiences
Objects falling to Earth is a human experience from birth. Since there is no visible cause for this phenomenon, it is assumed or taken for granted that objects will fall and no justification is necessary. 

Formative Assessment Question
Ask students to draw a free-body diagram including all of the forces acting on an object in free-fall.  Students can choose a launched projectile, a person jumping, an object falling, etc.  They should all look the same.

Interventions
Remind students of previous analyses using F=ma to describe objects moving from rest.  Also insist that students consider inertia and describe how that applies to an object at rest that suddenly falls.
Questions #11 and 12 in the Physics To Go questions address F=ma and identifying the force that is responsible for causing acceleration. This will help to bridge students from identifying an obvious force creating acceleration and identifying gravity as causing the same reaction.

References
Stead, K. and Osborne, R. (1980) Gravity, LISP Working Paper 20, Science Education Research Unit, University of Waikato, Hamilton, New Zealand.
Ruggiero, S., Cartielli, A., Dupre, F., Vicentini-Missoni, M. (1985) ‘Weight, gravity and air pressure: mental representations by Italian middle-school pupils’, European Journal of Science Education 7(2): 181-94.