Foundation · Explanatory preview
Reading a graph
A graph plots dependent outputs against independent inputs on two axes. The slope measures the rate of change and the area under a curve represents an accumulated sum.
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How does a curve show the relationship between two physical quantities?
The horizontal axis (abscissa) typically shows the independent variable, like position x or elapsed time t. The vertical axis (ordinate) shows the quantity that depends on it, like particle count or probability density p(x).
A flat horizontal line means the quantity does not change across the axis. A rising curve has positive slope (increasing rate), while a symmetric bell-shaped curve shows high concentration in the centre with tails tapering toward zero on both sides.
One worked example
- Plot particle positions −3, −1, +1, +3 along the horizontal axis with a vertical bar for particle count.
- The graph shows symmetric spread centered at zero.
- The average position is 0, but the points are visibly separated from the origin.
A stopping point: Check axis labels, units, and whether the curve represents a count, a density, or an accumulated total.
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