Distinguish fog from mist on a cold surface

Place a clear container against dark card and arrange side lighting. Add a small amount of warm water and use a chilled cover while observing from the side.

Place a transparent jar containing a little warm water below a chilled cover. 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.

An illuminated region can drift inside the jar while wall droplets stay attached. Repeat a simple comparison and keep the starting conditions as similar as the setup allows. Where a ruler, timer, or camera is involved, read it in the same way each time. A handful of consistent observations is easier to interpret than a long list collected under changing conditions.

Notice whether a pale patch drifts through the air or stays attached to the glass. Observe how the view changes when the cover comes back to room temperature.

Moisture on the outside may obstruct what you think is an internal cloud. Use the empty setup once before introducing the change you want to study. A baseline can show motion from a loose support, light falling on the screen from another direction or variation in the way the sample starts. Record what you see at that stage as part of the experiment.

Look from a second side where the outer glass can be wiped and observed. 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.

Describe separately what changes when the cold cover is removed. 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.

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. Draw the outer condensation as dots against the jar wall and use shading for anything visibly suspended between the glass sides. 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.

Make a drawing with separate labels for a droplet stuck to the wall and any haze you saw inside. 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.