Research: Gunstone, Mulhall & McKittrick (2007) Net force is a valuable construct that has no separate existence of its own, unlike the real forces acting on the object, i.e. The net force is the combined effect (the sum) of the real forces acting on the object. Research: Gunstone, Mulhall & McKittrick (2007) Scientific view Students often struggle to grasp the concept of net force, and often think it is an extra force in addition to the actual forces on an object. Research: Champagne, Klopfer & Anderson (1980), Gunstone & Watts (1985), Gunstone, Mulhall & McKittrick (2007), Osborne & Freyberg (1985) This may be partly a terminology problem: what students label as a force in these situations is similar to what scientists call ‘momentum’. Some students also strongly believe that this force is being used up if the object is slowing down. These ideas are also discussed in the focus ideaĪ common view that persists at this level is that a moving object must have a force acting on them in the direction of their motion. These rules appear to work when students ignore friction and air resistance friction and air resistance are generally not seen by students as involving forces. Students often have a set of ‘intuitive rules’ that seem to explain everyday examples of motion (see the teaching ideas on forces and motion at the lower levels). Research: Champagne, Klopfer & Anderson (1980), Trowbridge & McDermott (1981), Loughran, Berry & Mulhall (2006) Students seldom identify a car turning a corner at constant speed as accelerating because their common understanding requires the object to be changing speed for it to be accelerating.Įven senior students regularly confuse ‘acceleration’ and ‘speed’ for example they may think that if speed is increasing then acceleration is also increasing.

However, it is much more difficult to determine if an object already moving is changing its speed unless the change is dramatic. Students are familiar with objects accelerating from rest or braking, for example a car speeding up or to a lesser extent slowing down at the traffic lights. Accelerated motion is also a difficult concept for students because it occurs when an object changes It is very difficult to tell with the naked eye if an object is accelerating (for example, a ball flying through the air) and so students do not tend to think of motion in terms of whether it is accelerated or not. Contrasting student and scientific viewsĬontrasting student and scientific views Student everyday experiences.

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