Science · Physics
Chapter 1: Measurement and Motion in One Dimension
Not a picture of the journey.
Ana's phone logs a car pulling away on a perfectly straight road, and its position–time graph curves upward. Later the car rounds a bend at a steady 15 m/s, and the graph is a straight line.
How can the graph curve when the road does not, and be straight when it does?
Make your guess to turn the page.
Still to come: 10 pages · Lab · Words to Know · What We Learned · 4 questions · Explain It in Writing · Open Questions
The idea this lesson is working on — Students read motion graphs as pictures of the journey: a curve is a bend, a rising line is uphill, a flat line is stopped. The book sets that against a straight road that gives a curved graph and a bend that gives a straight one. Ask: what is on the vertical axis, and what is the slope of this graph? The idea to reach is that the graph shows one quantity against time, never a path.
Slope and area both mean something — On a velocity–time graph the slope is acceleration and the area underneath is displacement, with area below the axis counting as negative. The bend in the phenomenon is described in path length along the road; its velocity as a vector changes direction, which is a centripetal acceleration and belongs to two-dimensional motion.