Natural Science - Year I
Unit 9: Characteristics of Motion
Parents Guide for Unit 9
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Unit 9: Greek Theories of Motion
Preparation
- History Web Lecture: The lecture summarizes the definition of motion as a property of matter for several prominent Ionian philosophers. This kind of reading is frequently difficult for students because they assume that everyone has the same, to them obvious, understanding of these basic concepts. One of the purposes of having them read some of these different ideas is to force them to reconsider their own assumptions. Do they really know what motion is? How could they explain it from their own experience? How do they measure it if they don't have a good clock available?
- Science Web Lecture: The science weblecture has two goals. One is to define the terms we use in motion study (distance/displacement, speed/velocity, acceleration) and give examples. The other is to introduce the student to the idea of graphing data, and looking at the shape of the graphed line for information. If we graph distance along the y axis and time along the x axis, the line will tell us something about both velocity and acceleration:
- A level or horizontal straight line means that distance from some point of origin is constant. Since the object is not changing position, the slope of the line is zero and velocity is zero.
- A straight line with a positive slope (going up to the right) means that velocity is constant and distance is increasing.
- A straight line with a negative slope (going up to the left) means that velocity is constant but distance is decreasing.
- A curved line means that velocity itself is changing; the object is being accelerated or decelerated.
Scientists frequently use such graphs to make rapid assessments of a situation, much the same way we look at analog clocks to determine "how much time is left" without actually doing the math.
- Homework: The first part of the mastery exercise requires students to identify the major players in defining motion to the ancient Greeks and differences in their theories; this should be relatively straightforward from the history lecture. The second part of the mastery exercise asks them to describe a journey based on graphical information, use data to determine average velocities times, and calculate acceleration. These calculations have examples in the lecture.
- Discussion: Our discussion will focus on how we observe something as basic as motion, how we calculate velocity and acceleration from basic distance data, and how we use graphs to represent data.
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