MW2 Observe and describe the motion of everyday objects
Suggested time: 3-5 hours
Although students have observed and described motion throughout their lives, research shows that students often have developed misconceptions about the concepts of distance, speed, and acceleration. Thus, students need multiple opportunities to observe objects moving in a variety of contexts to help develop strong conceptual understandings of motion-related concepts. These contexts should include observations of real-time motion and recorded motion (e.g., video or television). The contexts should range from the motion of everyday objects to the largest and smallest extremes (e.g., stars and planets, atoms and sub-atomic particles) in order for students to understand that all types of motion share common characteristics.
The role of language in developing and sharing understanding is critical for this objective. Students should initially use everyday language to describe motion concepts but by the end of this unit, students should be able to use and understand appropriate kinematics terminology. The use of mathematical analysis of motion or problem solving using the equations of motion as an introduction to understanding motion concepts is strongly discouraged. Those approaches should follow, rather than precede, activities that support the development of conceptual understandings of position, speed, and acceleration.
Learning Objectives
- Observe and describe the motion of everyday objects qualitatively using personal words and phrases. (COM)
- Categorize the motion of everyday objects as uniform and non-uniform. (CCT)
- Operationally define uniform and non-uniform motion.
- Discuss the role of "frame of reference" in determining whether an object is in motion. (TL)
Key Questions
- How can you tell if an object is in motion?
- How can you tell if an object is speeding up or slowing down?
- How can you tell if an object is undergoing uniform motion?
- How does the choice of frame of reference influence the observation of motion and the motion itself?
- How can you use your own movements to represent uniform and non-uniform motion?
Key Concepts
- Motion at a constant speed in a straight line is called uniform motion .
- All motion is measured relative to some frame of reference chosen by the observer.
- Scientific knowledge is based on observation.
- An operational definition in the physical sciences explains how to measure the quantity being defined.
Pre-Instructional Questions
- What is the students' understanding of the term motion ?
- Are the students able to identify when an object is in motion?
- Do students understand the differences between uniform motion and non-uniform motion?
- Are students able to discuss the value and limitations of using their senses to collect data?
- Do students know the typical range of speeds for common objects (e.g., human walking, animal running, bicycle, automobile, commercial airliner, space shuttle, planet)?
Suggested Teaching Strategies and Activities
- Students should observe the motion of everyday objects (e.g., bicycles, rollerblades, wheelchairs, ice skates, skateboards, skis, automobiles, birds, and animals) and write descriptions of the motion. Students should be encouraged to use their own words, such as "speeding up", "slowing down", "faster", and "slower", to describe motion. Students should compare these types of motion and their perceptions of motion from live observations with examples from student or teacher-made videos or from television programs. Students can use these descriptions to identify characteristics of different types of motion and then group together examples that demonstrate uniform motion and examples that demonstrate non-uniform motion. (COM)
- Students should identify terms that people use to describe motion (e.g., speed up, slow down, fast, slow, motionless, stationary). Students could create visual representations of their understanding of relationships between these terms by using graphical organizers such as concept maps, webs, or lists. These can be used later in the unit to help students develop appropriate kinematics vocabulary to identify motion-related concepts.
- Students could use a ticker-tape timer to create tapes of different kinds of motion. Students could attempt to pull the tape at a constant speed, at a variety of speeds, or at a constant acceleration. Alternatively, students may connect the tape to a motorized toy that moves at a constant speed. Students should be able to recognize that the spacing of the dots is a visual representation of the motion of the object. Further, students should recognize that a pattern of equally spaced dots represents uniform motion and a pattern of unequally spaced dots represents non-uniform motion. At this point, it is not necessary for students to conduct any quantitative analysis of the motion by measuring the distance between dots.
- Students should discuss the role of observation in developing scientific knowledge and understanding after they have observed everyday objects in motion and identified examples of objects that sped up, objects that slowed down, and objects that moved at a constant speed in a straight line (uniform motion). It is likely that students will have difficulty categorizing every example of motion when they rely solely on visual observations. This discussion could provide a context or motivating factor for students to explore quantitative methods of describing and analyzing motion. (TL)
- Students should discuss the role of technology in attaining information about the motion of an object. For example, although our bodies can "feel" changes in speed (of sufficiently high positive or negative values) in instances such as amusement park rides, elevators, or automobiles, we are generally unable to determine if we are actually moving. Consider a student lying in the back seat of a car on an incredibly smooth road, wearing headphones so that they cannot hear any road noise or wind noise. How is it possible for the student to tell whether they are moving or not moving, or how fast they are moving?
- Students could explain how you can tell if an object is in motion. Their explanations can provide the context for introducing the concept of frame of reference. Consider the example of a person walking forward or backward on a moving bus, or handing an object to another person on a bus while the bus is moving. How does that motion appear to the people involved in the motion, to others on the bus, and to someone standing on the street watching the bus pass by? Do they all see the same set of motions? Would they all agree on quantitative measurements of the motions? Micro or macro scale examples of frame of reference might include discussing how we can tell that sub-atomic particles vibrate or that stars move in the universe. (CCT)
- Students could create a video that demonstrates their understanding of motion-related concepts. Such a video might include edited clips from TV (sporting events, car chases in movies, everyday objects moving) and/or student-produced video of everyday objects in motion. The video might show examples of uniform and non-uniform motion, along with appropriate narration or titles.
- Students should attempt to move an object, or themselves, at uniform motion. This will strengthen students' connections between conceptual and kinaesthetic understandings of uniform motion. One method of monitoring students' ability to move at a constant speed is through the use of a motion sensor or range finder. These technologies create real-time distance-time or speed-time graphs of objects that move in front of the sensor, typically within a range of 0.5 - 10 m. Students can move and monitor their motion, or they can move to try to match a pre-determined distance-time or speed-time graph.