CTS Guide: Force and Motion, pp 176-177- Section IV Research Summaries

Concept of Force

  • The way children think about forces is related to their meaning for the word force. Some students associate force with coercion, physical activity, muscular strength, or living things. Students generally appear to think of force as a property of a single object rather than as a feature of interaction between two objects (Driver et al. 1994).

Electrical Force

  • Younger students sometimes confuse repulsion and attraction between static charges as magnetism (Naab and Henry 2009).

Describing Motion

  • Younger children typically start to describe motion by identifying the direction in which an object moves, without regard to the speed of the object. As the sophistication of their ideas progress, they may use a “snapshot” description, in which they compare the speed of an object at different locations or instants. (In a “snapshot” description, students describe what is essentially a still photograph of an object, without looking at changes.) Eventually, older children can be led to describe how the speed of an object is changing at a specific location or instant (Dykstra and Sweet 2009).

  • Researchers have pointed out that students need opportunities to develop the appropriate language tools to describe motion.These tools include vocabulary, graphical representations, and numerical formulas. They use everyday terms such as going faster in ambiguous ways, sometimes referring to the magnitude of the speed of an object and at other times referring to the speed increasing with time. Terms like velocity and acceleration are not commonly used by school-age children before the terms have been introduced in science lesson (Driver et al. 1994).

  • Some students think acceleration is due to an increasing force (Twigger et al. 1994).

  • Mathematical studies reveal that few children recognize that any point on a measurement scale can serve as a starting point for describing motion. They tend to read off whatever number is the end point. Even students up through fifth grade have been shown to have this tendency (Lindquist and Kouba 1989).

  • It is quite common for students to confuse the concept of acceleration with the concept of velocity (Trowbridge and McDermott 1981).

Interpreting Motion Graphs

  • A study conducted by Kozhevnikov (2007) showed a correlation between spatial reasoning ability and the ability of students to correctly interpret motion graphs.

  • Students often experience difficulty interpreting the slope of a graph and sometimes confuse the height of the graph with the slope. Many students interpret graphs as literal pictures rather than symbolic representations (McDermott, Rosenquist, and van Zee 1987).

  • Many students interpret distance/time graphs as the paths of actual journeys (Kerslake 1981).

Constant Speed

  • Many researchers have found that substantial numbers of students are strongly committed to the idea that constant speed implies that a constant force is being applied to a moving object (Driver et al. 1994).

Circular Motion

  • Students often expect that objects moving in a curved path because of a wall or constraint will continue to do so when the wall or constraint is removed. This belief that the wall or constraint “trains” the object to follow a curved path is deeply rooted in students and persists even with targeted instruction. Many students think that objects in circular motion are being “thrown outward.” This is likely because of the sensation that they feel when traveling around curves in vehicles themselves (Arons 1997).

  • Students’ experiences with whirling objects on a string may contribute to their confusion about the direction of the force the string is exerting on the object. Students may think that they are exerting force along the circular path of the object’s motion, rather than perpendicular to it, toward the center (Arons 1997).

  • Students have difficulty perceiving the direction of motion in a straight line when they encounter situations like an object set in motion inside a curved hollow tube. In this case many students, including those in high school, think the object continues to travel in a curved path when it comes out of the tube (Gunstone and Watts 1985).

Falling Objects

  • Students do not always identify a force to account for falling objects. They think objects “just fall naturally” or that the person letting go of the object has caused it to fall. Students, including university students tend to think that heavier objects fall to Earth faster because they have a bigger acceleration due to gravity (Driver et al. 1994).

  • Studies by Osborne (1984) found that students think heavier objects fall faster.

Weight, Gravity, and Pressure

  • The idea that the weight of an object is a force—the force of gravity on that object— does not appear to be a firmly held idea among secondary students (Driver et al. 1994).