Student Conception: Friction and inertia

[admin]

Seed a discussion with a review of literature for misconceptions (Scott and Matt’s research)

[Matt Anthes-Washburn]

Student Conception: Friction and inertia
Students may confound friction with inertia.

Identifiers
Students may say that the force required to accelerate an object at rest is working against friction, not inertia.
(Atlas of Science Literacy (2001), American Association for the Advancement of Science, Project 2061. pp.62-63) (Jung et al., 1981; Brown & Clement, 1992)

Confounding Experiences
Pushing a massive object across a frictional surface makes it difficult to differentiate what force is required to accelerate an object and what force is required to overcome friction.  It is difficult to create a frictionless environment on earth.

Formative Assessment Question
Have students draw a free body diagram indicating the forces acting on the object.  Ask the students to calculate the force balance and determine what force would cause acceleration. 

Interventions
Pay particular attention to the case where the object moves with constant speed when a constant force is applied.  Students may need some help determining when they are pulling an object with constant speed.  They will also need to work through the example to understand why constant horizontal speed can be accurately correlated with constant force.  PTG #4 describes a cross-country skier in this situation. A constant force is applied to counter friction and no acceleration occurs.

[Ken Dugan]

The activity involves pulling different shoes across the desk or floor. perhaps giving the students similar materials to test to get a 'baseline' of data to make further comparisons would be . that way they could see that the Mu does not change unless the surfasces are changed.

[Janie Martin]

We wrapped a brick with different materials ( such as waxed paper, foil, felt etc) to compare the mu of different things but kept the mass constant.

[Janie Martin]

The activity involves pulling different shoes across the desk or floor. perhaps giving the students similar materials to test to get a 'baseline' of data to make further comparisons would be . that way they could see that the Mu does not change unless the surfasces are changed.

This is verry do-able because all you need are shoes and spring scales, good activity.

[Janie Martin]

ok heres something for you