Learners’ ideas

Students have common patterns of reasoning, which are often resistant to change.

• If there is motion, there must be a force in the direction of motion; this is widespread and highly resistant to change.
• The upward force on an object can continuously weaken/diminish and be overcome by the weight
• There is a force inside a moving object keeping it going and causing it to have some speed, which can get used up. "The force can fade away as the object moves along."
• Contact forces come only from active sources of power. For example, friction is not a force for most students, because you cannot see where it is coming from: there is nothing moving to produce it. Instead, friction is seen as a directionless resistance to movement. A table cannot produce a normal force upwards on an object resting on it, because the table is not seen as an active source of power. Rather students may view the table as a 'barrier'.
• A stronger force will completely dominate a weaker force.
• Rest is perceived as fundamentally different from motion. This lends support to the impetus theory, which makes a fundamental distinction between motion and rest. Impetus forces are assigned only to moving objects, whereas in Newtonian physics, rest is seen as one point in a continuum of possible positive or negative motion in a particular frame of reference.
• There is an impact force of momentum. For example, a student may say that when you catch a baseball you can feel the force coming out into your hand. This supports the idea that there is a force in the object as it comes toward your hand. 
• There is no concept of acceleration or it has been confused with the concept of speed. This makes it impossible for the student to conceive of force being connected to acceleration.

Further suggestions

• Ask students to articulate preconceptions so that they can be discussed; arrange laboratory experiences in conflict with preconceptions; and ask students to translate between graphs, tables, equations and verbal descriptions in a consistent manner.
• Develop metaphors which organise intuitions the student already has. In this approach, to explain the deceleration of an object experiencing friction, the student must reject the dying away model and learn to use a metaphor like viewing the situation as an external frictional force which erodes the velocity.