Physics Topic
Best-Fit Line Graphs
- Read notes
- Flashcards
- Quiz
- Confident
Study focus - 3 things
- Physics graphs should have labelled axes, suitable scales, accurate points, and a clear best-fit line
- A best-fit line shows the general pattern of data and should not simply join dot to dot
- Gradient can be found from two well-spaced points on the best-fit line
Section 1Setting up axes
Put the independent variable on the x-axis and the dependent variable on the y-axis. Label each axis with the quantity and unit, such as time / s or distance / m.
Section 2Choosing a scale
Choose a scale that uses most of the graph paper and is easy to count. Avoid awkward scales unless the data requires them. Equal spaces on an axis must represent equal increases.
Section 3Plotting points
Plot points carefully using small crosses or neat dots. Check each value before drawing the line. In a lab exam, one wrongly plotted point can change the pattern.
Section 4Drawing the best-fit line
A best-fit line is a smooth straight line or curve that follows the overall trend. It should pass close to most points, with points balanced on both sides where possible. Do not join every point with zigzag lines.
Section 5Finding gradient
For a straight best-fit line, choose two points on the line that are far apart. Calculate gradient as change in y divided by change in x. Use points on the line, not necessarily original data points.
Examples
A student records time and distance. Which axis should time usually go on?
Time is usually the independent variable, so it goes on the x-axis. Distance goes on the y-axis.
A best-fit line passes through (2, 4) and (6, 12). Find the gradient.
Gradient = change in y / change in x = (12 - 4) / (6 - 2) = 8 / 4 = 2.
Now let's water it
Session runs notes to flashcards to quiz back-to-back.