Draw the paths followed by points on a rolling wheel

Make a cardboard wheel with a centre mark and one rim dot. Start with the rim dot at the bottom and draw a baseline on transparent paper over a guide.

Draw a visible dot at the rim of a cardboard wheel and use a ruled baseline to guide its roll. If the results vary, look for a second feature that moved along with the one you meant to change. That can be the distance to an observer, the angle of a support or the way the material moves between runs. Isolate it in a small follow-up trial when possible.

The centre stays at one height while the rim mark rises and falls through the turn. Observe the setup from the same place in each trial. A view from farther away can hide a shallow curve or make two positions look aligned. A short guide mark shows the place you used. Keep the recording method fixed as well when changing the setup itself is the point of the comparison.

Roll the circle carefully without sliding it. Mark both points after each small turn, then connect the centre marks and the rim marks in separate sequences.

Sliding at release creates offsets that can obscure where the dot touches down. Decide how to mark an observation when two readings fall too close together to separate. Even spacing on a sheet is useful only to the extent you can see where a feature crosses each line. A visible range can carry more meaning than a single estimated digit that your instrument cannot resolve.

Roll through shorter steps while matching a series of circumference marks to the baseline. Put the observations into order and keep the raw measurements or drawings. A result can be useful at more than one level. The direction of a change may be unmistakable while the exact size is uncertain. Describe the strongest pattern the records support and qualify measurements that depend on a faint boundary or a moving object.

Mark the midway position and compare the rim height against the centre height. Sketch your apparatus before you start and use the sketch to identify where each observation will be made. Write down the starting state before changing it. If another person repeats the trial, knowing the relative positions can matter more than the brand or appearance of the materials.

Write a row for each run and keep apparently odd results in the record. Mark things that went wrong, such as a shifted surface, uneven starting point or missed time, before judging the pattern. Changing how you record the behaviour halfway through can make two otherwise similar trials difficult to compare. Explain the outcome in a sentence that a reader can check against the figures or sketch. Use a second sentence for a proposed cause. If you can imagine a different cause that fits the same observations, describe a small test that would help distinguish the two. Comparing those predictions can make a follow-up clearer than simply repeating the same demonstration. Trace an additional point halfway between centre and rim if both primary paths are readable. Its path should show a smaller upward and downward swing. A useful prediction can say which direction an effect should move without specifying its exact size. Put that prediction next to the expected observation time or distance. If the pattern appears in the other direction, note how you would test whether it arose from a measurement condition or from your original explanation.

Compare the height of the rim at the start, midpoint and end of one full revolution. Write the independent change at the start of each row and keep the outcome beside it. Include anything about a failed run that would matter to somebody repeating the setup. If you later make a neat graph, keep the rough record as well so it remains possible to inspect the reasons for leaving out a point.