Final answer:
To calculate the average rate of plate movement, a best-fit line is drawn through the origin and data points on a graph. The slope calculated from the best-fit line represents the average rate of movement. This rate, usually around 4 to 5 cm per year, is recorded on the graph.
Step-by-step explanation:
To determine the average rate of plate movement in centimeters per year using a graph, you start by plotting all the given data points that represent plate movement over time. Once all points are plotted, use a straight edge to draw a best-fit line through the origin (0,0) and across the cloud of data points, approximating the general trend of the data. This line may not pass through every point but should reflect the overall direction of the dataset.
After drawing the line, you calculate the slope, which is the ratio of the vertical change (rise) to the horizontal change (run). To find the rate of plate movement, pick two points on the line, preferably far apart for more accuracy, and divide the difference in their y-values (rise) by the difference in their x-values (run). This calculation gives you the slope, representing the average velocity or rate of movement of the plates in centimeters per year. Record this value on the graph where it is easily visible.
Remember, this method reflects the relative motion between two tectonic plates, which typically move at a rate comparable to the growth of human hair, about 4 to 5 centimeters per year.